# Climate in Plain Sight — full text

> Climate in Plain Sight is an independent publication that explains climate science, impacts, and responses for curious non-specialists. It connects physical mechanisms to evidence and everyday decisions without sanding off uncertainty or serving doom by the bucket.

# Climate Change Around 2040: Reading the Projections

> Climate change around 2040 means a warmer global climate with increasing heat hazards, continued sea-level rise and regionally different water-cycle changes—not a forecast for one year's weather. Read projections with their averaging period, historical baseline and emissions scenario. Some near-term changes occur across the assessed pathways, but their later magnitude and the damage people experience remain responsive to emissions and adaptation. Global averages cannot determine a property's safety; use qualified local assessment and current official hazard guidance.

Source: https://climateofourfuture.org/climate-change-by-mid-century/  
Publisher: Climate in Plain Sight  
Published: 2026-09-08  
Updated: 2026-09-08

## What does climate change around 2040 mean?

Climate change around 2040 means a warmer global climate with increasing heat hazards, continued sea-level rise and regionally different water-cycle changes—not a forecast for one year's weather. Read projections with their averaging period, historical baseline and emissions scenario. Some near-term changes occur across the assessed pathways, but their later magnitude and the damage people experience remain responsive to emissions and adaptation. Global averages cannot determine a property's safety; use qualified local assessment and current official hazard guidance.

The useful question is not simply “What happens in 2040?” It is: which evidence applies to the period and decision you actually mean? A long-term home, a seasonal event and a drainage design require different information.

This guide reads the Intergovernmental Panel on Climate Change's Sixth Assessment Report, or IPCC AR6. Its findings are assessment results, not newly calculated forecasts or claims that we ran a climate model.

## Is 2040 a year or an averaging window?

In AR6's physical-science assessment, the **near term** is 2021–2040 and the **mid-term** is 2041–2060. These are 20-year windows. A result for the first window is not a result for its final year alone. [IPCC Chapter 4](https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-4/)

“By mid-century” also needs clarification: a sea-level value for 2050 and a temperature average for 2041–2060 do not have identical time definitions.

Single years can rise above or below the underlying human-induced temperature trend because of natural variability. AR6 specifically distinguishes an individual year above a warming threshold from reaching that threshold as a sustained warming level. [IPCC physical-science summary, B.1.4](https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/)

Do not turn a graph's endpoint into a deadline before which nothing changes, or after which all locations experience the same conditions.

## How much global warming does the assessment project?

The following selected rows reproduce AR6 Chapter 4, Table 4.5's **very likely ranges** for global surface air temperature change. Both columns are relative to **1850–1900**, not additional warming from today.

| Emissions scenario | 2021–2040 average | 2041–2060 average |
| --- | ---: | ---: |
| SSP1-1.9 | 1.2–1.7°C | 1.2–2.0°C |
| SSP2-4.5 | 1.2–1.8°C | 1.6–2.5°C |
| SSP5-8.5 | 1.3–1.9°C | 1.9–3.0°C |

These are conditional assessment ranges, not three competing weather forecasts. The table does not rank the scenarios by probability.

Notice that the near-term ranges overlap substantially. The mid-term comparison separates more, especially between the lowest and highest pathways shown. Similar near-term outcomes therefore do not establish that emissions choices are irrelevant.

For the meaning of the labels, use our [SSP scenario decoder](/climate-scenarios-ssp-pathways-explained/); for how evidence becomes a projection, see the [climate-models pillar](/climate-future-what-models-project/). This article's task is to connect the assessed horizon to the right question.

## What changes should a reader distinguish?

### Heat is not just an annual mean

NASA identifies longer, more intense heat waves among climate effects already observed, and explains that future effects depend on emissions. These are ongoing changes, not conditions that begin only in 2040. A global mean temperature change is not the number to add to every afternoon forecast or use as a workplace heat limit. Extreme-event information needs its own variable, geography and time window. [NASA climate-effects overview](https://science.nasa.gov/climate-change/effects/)

Ask whether a local product describes average summer temperature, hot nights or the frequency of a defined extreme. Those are different questions, even when displayed with the same color scale. During actual heat, follow current local public-health and weather guidance rather than a distant climate projection.

### Rainfall averages and heavy rain are different quantities

AR6 projects heavier and more frequent heavy-precipitation events in most regions with additional warming, while regional and seasonal water-cycle changes are uneven. [IPCC physical-science summary, B.2–B.3](https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/)

A chart of annual rainfall totals does not answer a question about short-duration downpours. Nor does either chart, by itself, calculate flood depth. Keep the measurement definition attached when asking a local authority or qualified specialist what additional evidence is needed.

### Sea level uses another baseline and range convention

AR6 Chapter 9 projects global mean sea-level rise by 2050, relative to **1995–2014**, with likely ranges of **0.15–0.23 metres under SSP1-1.9** and **0.20–0.29 metres under SSP5-8.5**. These projections consider processes assessed with at least medium confidence; deeply uncertain ice-sheet processes are not included in those likely ranges. [IPCC ocean and cryosphere assessment](https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-9/)

Do not confuse these likely sea-level ranges with the temperature table's very likely ranges. Local relative sea level also depends on land movement and regional ocean processes. Neither global range is a property-level flood height or a safe clearance.

The chapter also assesses continued sea-level rise beyond 2100. Reaching the end of a planning period does not end the physical response.

## What does natural variability leave unresolved?

**Internal variability** is fluctuation arising within the climate system. Regional outcomes combine that variability with human influence, natural external influences and regional processes.

IPCC Chapter 10 finds that internal variability can delay the emergence of human influence in regional mean precipitation. It also warns that increasing model resolution alone does not solve every performance limitation. A more detailed-looking map is not automatically a more dependable answer for your use. [IPCC regional-climate assessment](https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-10/)

This is a reason to examine several lines of evidence, not to discard the global warming finding. Record whether a regional assessment discusses observations, different models, variability and relevant local processes. If it reports disagreement, retain that disagreement in your notes.

## Does an unavoidable hazard mean unavoidable damage?

No fixed amount of damage follows automatically from a global temperature value. IPCC's impacts assessment distinguishes the physical hazard from **exposure**, meaning who or what is affected, and **vulnerability**, meaning susceptibility to harm.

Its near-term assessment emphasizes that risks depend strongly on changes in exposure and vulnerability, and that adaptation can moderate several risks. Limiting warming reduces projected losses relative to higher warming, but cannot eliminate every loss. [IPCC impacts summary, B.3](https://www.ipcc.ch/report/ar6/wg2/chapter/summary-for-policymakers/)

Avoid both extremes: a future problem is not solved because an adaptation plan exists, and an ongoing physical change does not make every protective decision futile. Ask who is responsible for implementation, maintenance and updating evidence.

## How can you turn the horizon into useful questions?

Consider this original fictional planning exercise: a community group wants to assess a venue for activities extending into 2050. No venue, climate dataset or safety evaluation has actually been examined.

Replace “Will this place be safe in 2040?” with a short evidence-request record:

| Question | Information to request |
| --- | --- |
| What period covers the intended use? | Exact years, plus any longer life of the building or equipment |
| Which concern is being assessed? | Separate heat, rainfall, coastal water level and service interruption questions |
| What does the source measure? | Variable, units, baseline, averaging period and uncertainty |
| Who can interpret local implications? | Relevant authority and appropriately qualified professional |
| What remains unresolved? | Missing local information, assumptions, responsible person and review date |

Do not give the record a numerical safety score. Its purpose is to identify missing evidence, not certify the venue. Urgent hazards require current official instructions immediately, regardless of whether this document is complete.

A warming-level map creates a different question again. The Met Office explains that such maps examine conditions at a specified amount of global warming without assigning that level one universal date. They cannot simply be relabeled “2040.” [Met Office projection guide](https://www.metoffice.gov.uk/blog/2023/making-sense-of-climate-change-projections)

## What should stay in the final conclusion?

Keep three statements separate: what the assessment projects, what a regional product says, and what a qualified decision-maker concludes for a particular use. Write down the source version and unresolved questions alongside each.

The [climate basics section](/climate-basics/) supplies background terminology. The practical result here is a better-framed request for evidence—not a location recommendation or permission to wait until mid-century before addressing present hazards.

## Sources

- [NASA Science: climate effects](https://science.nasa.gov/climate-change/effects/)

- [IPCC AR6 Working Group I Chapter 4: Table 4.5 and future global climate](https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-4/)
- [IPCC AR6 Working Group I Summary for Policymakers](https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/)
- [IPCC AR6 Working Group I Chapter 9: ocean, cryosphere and sea level](https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-9/)
- [IPCC AR6 Working Group I Chapter 10: regional climate information](https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-10/)
- [IPCC AR6 Working Group II Summary for Policymakers: near-term risks](https://www.ipcc.ch/report/ar6/wg2/chapter/summary-for-policymakers/)
- [Met Office: Making sense of climate change projections](https://www.metoffice.gov.uk/blog/2023/making-sense-of-climate-change-projections)

## Frequently asked questions

**Can climate science predict the weather in 2040?**

A long-term projection is not a forecast for one distant day or year. Read the source's time window, baseline, scenario and uncertainty. For an event or immediate hazard, use current official forecasts and instructions. A global assessment cannot establish local travel, property or venue safety.

**Are the temperature ranges additional warming from today?**

Not in the table shown here: its reference is 1850–1900. Treating that historical baseline as today's temperature would misstate the result. Copy the reference years whenever you record a value, and do not compare another chart until its variable, period, baseline and uncertainty convention are clear.

**Does a global sea-level projection show whether a property will flood?**

No. Global mean sea level is not local relative sea level, and neither is automatically flood depth at an address. Local land and ocean processes and other site-specific evidence matter. Use current official local information and qualified assessment for consequential decisions, and follow emergency instructions during an active hazard.

**Why can local outcomes remain uncertain while global warming is clear?**

Regional climate combines human influence with internal variability and regional processes. The IPCC finds that variability can delay the emergence of a human influence in regional mean precipitation. Uncertainty about the local pattern does not erase global evidence; it means the local question needs suitable evidence and qualified interpretation.

**Does similar near-term warming mean adaptation and emissions cuts do not matter?**

No. Similar near-term assessment ranges do not make later pathways identical. The impacts people experience also depend on exposure, vulnerability and adaptation. Keeping these questions separate avoids treating either emissions cuts or adaptation as a complete substitute for the other. No measure should be read as a guarantee of safety.


---

# Climate Change and Extreme Weather: What We Know

> Human-caused climate change changes the likelihood or intensity of many extremes rather than acting as the sole cause of every event. The evidence is strongest for more frequent and intense hot extremes. Heavy precipitation has increased in many regions, while drought, tropical cyclones, wildfire, and floods depend more on regional conditions, event definitions, exposure, and other contributing factors.

Source: https://climateofourfuture.org/climate-change-extreme-weather/  
Publisher: Climate in Plain Sight  
Published: 2026-07-19  
Updated: 2026-08-25

## Climate change shifts the odds and intensity of extremes

Human-caused climate change is already affecting many weather and climate extremes in every region, but it does not influence every event in the same way. The strongest broad evidence concerns heat extremes: a warmer baseline makes unusually hot conditions more frequent and more intense. Heavy precipitation has intensified in many places, while conclusions about drought, tropical cyclones, floods, and fire weather depend more on the region, event definition, and contributing conditions.

The most accurate question is rarely “Did climate change cause this event?” Weather extremes have immediate physical causes, and damage also depends on where and how people build, prepare, and respond. Attribution science asks whether human influence changed an event's likelihood, intensity, duration, or affected area.

## What counts as extreme weather?

An extreme can be defined relative to a place and season, by a fixed threshold, or by its impact. A 95°F day may be ordinary in one climate and exceptional in another. A heavy-rain threshold that drains safely in one city may overwhelm another city's infrastructure.

Common categories include:

- Heat waves and unusually hot nights
- Heavy precipitation and flash-flood-producing rainfall
- Meteorological, agricultural, and hydrological drought
- Tropical cyclones and their rainfall, wind, and storm surge
- Conditions that support wildfire, often called fire weather
- Coastal flooding, including the influence of sea-level rise
- Compound events, such as heat combined with drought

These labels are not interchangeable. Drought can mean low rainfall, dry soil, reduced streamflow, or water shortage, each over a specified period. “Storms are worse” is not a scientific variable. Good analysis names the hazard and measurement.

## What the IPCC concludes

The IPCC's [Sixth Assessment synthesis headline statements](https://www.ipcc.ch/report/ar6/syr/resources/spm-headline-statements/) say human-caused climate change is already affecting many weather and climate extremes in every region. Its physical-science assessment distinguishes confidence by event type and geography rather than giving every row the same answer.

At a broad level:

| Hazard | Main climate connection | How carefully to state it |
|---|---|---|
| Heat extremes | Higher average temperatures shift the hot tail | Human influence has increased many hot extremes; evidence is strong |
| Heavy precipitation | Warmer air and changing circulation can increase intense rainfall | Increases are observed in many regions; local outcomes vary |
| Drought | Rainfall, evaporation, soil moisture, vegetation, and water use interact | Type and region must be specified |
| Tropical cyclones | Warmer ocean and air can affect rainfall and intensity; circulation also matters | Avoid claiming simple increases in every storm count |
| Wildfire | Heat and dryness can worsen fire weather; ignition and land management are crucial | Climate change affects hazard, not every ignition or loss alone |
| Coastal flooding | Higher mean sea level raises the starting point for storm tides | Sea-level rise increases flooding potential, while local subsidence and defenses matter |

The table is intentionally uneven. Scientific honesty sometimes looks less like a slogan and more like a drawer full of carefully labeled adapters.

## Heat: the clearest connection

When average temperature rises, the distribution of daily temperatures shifts. Hot thresholds are crossed more often, and extreme highs can become more severe. Changes in humidity, soil moisture, urban surfaces, and atmospheric circulation can further shape a particular heat event.

Nighttime heat matters as well as afternoon maximums. Warm nights reduce opportunities for bodies, buildings, crops, and ecosystems to cool. Urban heat islands can add local warming because dark surfaces absorb energy, vegetation is limited, and buildings alter airflow. That local effect and global climate change can operate together.

Attributing a heat wave involves comparing observations and models with a counterfactual climate that excludes human influence. Researchers may estimate how much hotter the event became or how its probability changed. Results apply to the defined event, region, dates, and methods—not automatically to every heat wave everywhere.

## Heavy rain and flooding are related but different

A warmer atmosphere can hold more water vapor, giving intense storms access to more moisture when other conditions support rainfall. Observations show heavy precipitation has intensified in many regions, and human influence has contributed to increases at broad scales.

But heavy rainfall is not the same as flood damage. Flooding also depends on:

- How wet the soil was before the storm
- Snowmelt or frozen ground
- River shape and reservoir operations
- Pavement, drainage, and development
- Building location and flood defenses
- The duration and path of the storm

Climate change can intensify the rainfall hazard while exposure and vulnerability determine much of the consequence. A paved watershed and a forested one can respond differently to the same rain. Likewise, improving drainage may reduce damage without changing the storm itself.

## Drought requires a full name

“Drought” can hide several processes:

- **Meteorological drought:** unusually low precipitation
- **Agricultural drought:** inadequate soil moisture for crops or vegetation
- **Hydrological drought:** low streamflow, reservoir, lake, or groundwater conditions
- **Ecological drought:** water deficits that stress ecosystems

Warming can increase evaporative demand and dry soils more quickly, worsening some droughts even when precipitation changes are modest. Yet circulation, snowpack, soil, vegetation, irrigation, and water management also matter. Some regions are projected to dry; others may become wetter on average while still experiencing dry spells.

This is why global claims such as “climate change causes all droughts” are indefensible. Specify the region, period, and drought measure. The evidence is still serious; it is simply not one-size-fits-all.

## Tropical cyclones: intensity, rain, and counts

Tropical cyclones draw energy from warm ocean conditions, but their formation and tracks also depend on wind shear, atmospheric moisture, circulation, and natural variability. Climate research does not support the cartoon claim that warming turns a dial labeled “more hurricanes everywhere.”

The better-supported concerns include heavier cyclone rainfall, a larger proportion of intense storms, and higher coastal impacts where sea-level rise elevates storm surge on top of a higher baseline. Changes in the total number of tropical cyclones are more uncertain and can vary by basin and model.

For any approaching storm, follow current official forecasts and emergency guidance. Climate attribution explains changing risk; it cannot tell a household whether today's evacuation route is open.

## Wildfire: climate affects the conditions, people often provide the spark

Wildfire requires fuel, ignition, and weather that supports burning and spread. Human-caused warming can contribute to hotter, drier conditions and longer periods of dangerous fire weather in some regions. Drought, earlier snowmelt, and vegetation stress can also affect fuel dryness.

At the same time, ignition sources, past fire suppression, land management, invasive plants, forest structure, and expansion of homes into fire-prone areas strongly shape actual fires and losses. Climate change does not light every match. It can make the landscape more receptive to fire once ignition occurs.

Separate four questions:

1. Did the weather favor fire?
2. How much burnable fuel existed?
3. What caused ignition?
4. Why were people and structures exposed?

Only then is “climate and wildfire” a useful analysis instead of a shouting match with smoke in it.

## Coastal flooding begins from a higher baseline

Global mean sea level rises as ocean water warms and expands and as land ice loses mass. Local sea level also reflects land movement, ocean circulation, and regional gravitational effects. When mean sea level is higher, a storm surge or high tide needs less additional height to reach damaging thresholds.

This connection is physically direct, but local impact still depends on shoreline shape, waves, tides, subsidence, drainage, wetlands, seawalls, and development. Adaptation can reduce risk through warning systems, building standards, restored natural buffers, drainage improvements, or planned relocation where necessary.

## How event attribution works

Rapid attribution studies generally follow a structured comparison:

1. **Define the event.** Researchers specify its dates, region, and metric—perhaps a three-day maximum temperature or seasonal rainfall deficit.
2. **Gather observations.** They assess how rare the event was in the current climate and whether the record is suitable.
3. **Model two worlds.** Climate simulations represent today's conditions and a counterfactual without the estimated human influence.
4. **Compare probabilities or intensity.** Researchers calculate how the event's likelihood or magnitude differs.
5. **Test uncertainty.** Multiple models, observations, and statistical methods reveal how robust the result is.

A conclusion may say an event became more likely, less likely, more intense, or show no detectable change. “No detectable change” does not prove no influence exists; the event may be too rare, the data too short, or the modeled process too uncertain. Conversely, a strong result is not permission to attach the same number to a different event.

## Hazard is only one part of disaster

Disaster risk grows from three interacting elements:

**Hazard** is the physical event, such as heat or floodwater.  
**Exposure** is the people, buildings, ecosystems, and infrastructure in its path.  
**Vulnerability** is how susceptible those exposed systems are to harm.

Climate change can alter the hazard. Housing policy, income, health, infrastructure, land use, warnings, and historical inequality shape exposure and vulnerability. Two neighborhoods under the same heat dome may face profoundly different danger if one has trees, reliable electricity, safe housing, and accessible cooling while the other does not.

This framing avoids two mistakes: pretending climate has no role because development matters, and pretending emissions are the only reason damage occurs. Both physical change and social conditions require attention.

## What changing extremes mean for action

**Mitigation** reduces greenhouse-gas emissions and protects carbon sinks, limiting the magnitude of future climate change. **Adaptation** reduces harm from changes already occurring or expected. Cutting fossil-fuel emissions is mitigation; updating heat plans, drainage, and building design is adaptation.

They work at different points in the risk chain. Adaptation can protect people during a heat wave, but it cannot prevent endlessly rising global temperatures if emissions continue. Mitigation lowers future hazard, but it cannot eliminate every impact already locked in. The practical comparison of [mitigation and adaptation](/climate-mitigation-vs-adaptation/) shows why treating them as rivals wastes time.

The physical foundation remains the [human-enhanced greenhouse effect](/greenhouse-effect-explained/). Added greenhouse gases shift the climate system's energy balance; weather then unfolds within that changed system. If the timescales still feel slippery, revisit the distinction between [weather and climate](/weather-vs-climate/).

The careful conclusion is also the useful one: climate change is changing extreme-weather risk, most clearly for heat and with important but more varied effects across other hazards. Precision does not weaken that finding. It tells communities which problem they are actually trying to solve.

## Frequently asked questions

**Does climate change cause extreme weather?**

Climate change can alter an extreme event's probability, intensity, duration, or affected area, but events also have immediate weather causes. Attribution science compares today's climate with a modeled world without human influence. The strength of the connection varies: evidence is especially strong for heat, while other hazards require more regional and event-specific analysis.

**Are hurricanes becoming more common because of climate change?**

Research does not support a simple claim that the total number rises everywhere. Better-supported concerns include heavier tropical-cyclone rainfall, a greater proportion of intense storms, and worse coastal flooding where sea level is higher. Formation and tracks also depend on wind shear, circulation, natural variability, and the ocean basin being studied.

**How does climate change make heavy rain worse?**

Warmer air can contain more water vapor, so storms may have more moisture available when atmospheric conditions produce rain. Heavy precipitation has intensified in many regions. Flood damage is a separate outcome shaped by soil moisture, drainage, river management, pavement, topography, defenses, and where people and buildings are located.

**Is every wildfire caused by climate change?**

No. Fires require ignition, fuel, and weather that supports burning. Warming can increase heat, dryness, and dangerous fire-weather conditions in some regions, but ignition sources, vegetation, past suppression, land management, and development in fire-prone places also matter. Climate change can worsen the conditions without supplying every spark.

**What is extreme-event attribution?**

Extreme-event attribution estimates how human influence changed a defined event's likelihood or intensity. Researchers specify the region, dates, and metric; analyze observations; simulate the present climate and a counterfactual without human influence; then compare results across models and methods. Conclusions apply to that event definition and should not be copied automatically to other events.

**What is the difference between a hazard and a disaster?**

A hazard is a potentially damaging physical event such as extreme heat or flooding. Disaster risk also depends on exposure—who and what lies in harm's way—and vulnerability, or susceptibility to damage. Climate change can alter hazards, while infrastructure, inequality, health, land use, preparation, and governance strongly shape whether a hazard becomes a disaster.


---

# Our Climate Future: What Models Actually Project

> Climate models project continued near-term warming, with greater heat and other risks as warming increases. They do not produce one fixed forecast: researchers run physical models under alternative emissions and land-use pathways, then assess ranges shaped by model response and natural variability. Late-century warming depends strongly on future emissions, while local impacts also depend on geography, exposure and adaptation. A projection is conditional evidence, not a prophecy.

Source: https://climateofourfuture.org/climate-future-what-models-project/  
Publisher: Climate in Plain Sight  
Published: 2026-09-05  
Updated: 2026-09-05

## What does climate science say about our future?

Earth will keep warming in the near term, but the amount of warming later this century is not fixed. Climate projections combine physical models with alternative emissions pathways, so they produce conditional ranges rather than one forecast. Some responses, including higher heat extremes and continued sea-level rise, are robust. Their eventual scale, many regional rainfall changes, and the human damage they cause still depend on emissions, natural variability, local exposure, and adaptation.

That answer contains two ideas that are often pulled apart. The future is constrained by physics: adding greenhouse gases changes Earth's energy balance. It is also shaped by choices: people determine a large part of the future emissions fed into the models. A projection is neither a calendar of guaranteed disasters nor a reason to assume everything remains negotiable.

## What is the difference between a projection and a prediction?

A prediction says what is expected to happen. A climate projection says what models show **if a stated set of conditions occurs**. The distinction matters because no model can know future energy systems, land use, technology, policy, population, or consumption in advance.

The US Fifth National Climate Assessment's [scenarios and datasets appendix](https://toolkit.climate.gov/sites/default/files/2025-07/NCA5_App3_Scenarios-and-Datasets.pdf) is explicit: climate-model output is neither a forecast nor a prediction. It is a conditional projection whose result depends on human choices and on how the climate system responds.

This does not make a projection empty. Conditional statements can be precise and useful. An engineer may not know how many people will cross a bridge in 2050, but can still calculate its response under specified loads. Climate scientists likewise compare the system under specified greenhouse-gas, aerosol and land-use pathways.

Weather forecasts are a different product. They begin with the atmosphere's current state and try to follow its detailed evolution over days. Climate projections ask how the statistics of weather change over decades as external influences change. Our guide to [weather versus climate](/weather-vs-climate/) explains why uncertainty about one Tuesday's rain does not erase information about a warmer long-term distribution.

## How are climate projections built?

Global climate models divide the atmosphere, ocean, land and ice into three-dimensional cells. Within and between those cells, equations represent conservation of energy and mass, fluid motion, radiation, clouds, the carbon cycle and other processes. Processes too small or complex to calculate directly at the grid scale are approximated using physically informed relationships called parameterizations.

A projection usually involves five layers:

1. **A scenario supplies external conditions.** It describes a possible path for greenhouse gases, aerosols, land use and other influences.
2. **A model calculates the response.** The model moves energy, water and carbon through its representation of the Earth system.
3. **Repeated runs sample natural variability.** Slightly different starting conditions can produce different sequences of El Nino events, circulation patterns and regional weather while sharing the same long-term forcing.
4. **Multiple models sample structural differences.** Research groups make different defensible choices about resolution and approximated processes.
5. **Assessments combine evidence.** Model results are evaluated alongside observations, paleoclimate records, process understanding and other lines of evidence.

Models are not accepted because their maps look sophisticated. Scientists test whether they reproduce important features of past and present climate, examine where they fail, compare independent models, and constrain results with observations. The [NOAA climate-model primer](https://www.climate.gov/maps-data/climate-data-primer/predicting-climate/climate-models) describes this cycle of physical equations, model comparison and checks against observed conditions.

A model is necessarily a simplified Earth. The relevant question is not whether it is perfect; no useful model is. The questions are whether it represents the process needed for the decision, whether known biases are addressed, and whether conclusions survive across methods and evidence.

## Why do projections use emissions scenarios?

Emissions scenarios are structured alternatives, not prophecies and not ranked betting odds. Modern assessments often use Shared Socioeconomic Pathways, or SSPs, paired with different levels of climate forcing. Each pathway supplies a coherent set of inputs with which models can ask: what follows if emissions fall rapidly, remain intermediate, or rise very high?

The scenario labels do not say which world will occur. The Fifth National Climate Assessment notes that its scenarios do not have relative likelihoods assigned. Calling the highest pathway "the prediction" is therefore wrong; calling the lowest pathway a promise is equally wrong.

The Intergovernmental Panel on Climate Change's Sixth Assessment Synthesis Report gives a useful view of the spread. For global surface temperature averaged over 2081-2100 relative to 1850-1900, its assessed best estimates and very likely ranges are:

| Greenhouse-gas pathway | Best estimate | Very likely range |
| --- | ---: | ---: |
| Very low, SSP1-1.9 | 1.4C | 1.0-1.8C |
| Intermediate, SSP2-4.5 | 2.7C | 2.1-3.5C |
| Very high, SSP5-8.5 | 4.4C | 3.3-5.7C |

These are 20-year global averages, not temperatures for one year, one city or one afternoon. The values also share a historical reference period; silently changing the baseline would change every number. The [IPCC Synthesis Report's headline findings](https://www.ipcc.ch/report/ar6/syr/resources/spm-headline-statements/) summarise the central result: continued greenhouse-gas emissions produce additional warming, while deep and sustained reductions slow that warming.

The table contains two different kinds of spread. The difference between rows is largely **scenario uncertainty**: society can still take different emissions paths. The range within a row includes uncertainty about how strongly the climate responds and how models and evidence represent that response. Neither should be collapsed into a single number with false precision.

## What parts of the climate future are most firmly constrained?

Some statements rest on well-understood mechanisms, observations and agreement across projections.

**Continued emissions produce further warming.** Carbon dioxide accumulates, and cumulative net carbon-dioxide emissions are closely related to global warming. The [greenhouse effect](/greenhouse-effect-explained/) is a measured physical mechanism, not an assumption added only when a model is run.

**Hot extremes become more frequent and intense as global warming increases.** A warmer temperature distribution shifts the conditions in which heat events occur. The change is not identical everywhere, and individual events still have immediate weather causes.

**The water cycle changes, but not uniformly.** A warmer atmosphere can hold more moisture, supporting heavier precipitation in many circumstances. Circulation, soils, seasons and geography complicate regional rainfall and drought. "Wet places get wetter" is not a universal local rule.

**Oceans and ice respond over long timescales.** Ocean heating, glacier and ice-sheet loss, and sea-level rise do not stop on the date printed at the right edge of a 2100 chart. Some long-lived responses continue after atmospheric temperature stabilizes, and their rate and eventual scale depend on the emissions path.

**Risks rise with each increment of warming.** This does not mean every hazard rises by the same percentage. It means a lower warming path generally carries lower climate-related risks than a higher one, all else equal. NASA's current [summary of climate effects](https://science.nasa.gov/climate-change/effects/) notes that effects already observed include ice loss, sea-level rise and more intense heat waves, while the severity of future effects depends on future human activity and total carbon-dioxide emissions.

For specific hazards, the level of confidence differs. The evidence for heat is especially strong. Precipitation, drought, wildfire conditions and tropical-cyclone characteristics require narrower statements about the variable and region. That evidence ladder is set out in our guide to [climate change and extreme weather](/climate-change-extreme-weather/).

## What is already constrained, and what remains open?

"Locked in" is useful only if its object and timescale are named. It can otherwise turn a physical constraint into a claim that choices no longer matter.

| More constrained by current conditions and physics | Still strongly contingent |
| --- | --- |
| Additional near-term global warming across the assessed pathways | The amount of late-century warming, especially between low and high emissions paths |
| Continued long-term sea-level response from ocean warming and land-ice loss | The rate and ultimate magnitude of sea-level rise |
| More heat risk as the global mean rises | The exact sequence of hot years and local heat events |
| Lasting effects from accumulated carbon dioxide | How quickly net emissions fall and whether temperatures stabilize at a lower or higher level |
| Unequal exposure to hazards already present | Future exposure, vulnerability, adaptation and resulting damage |

Even where a physical change is unavoidable, harm is not a fixed output of temperature alone. A flood becomes a disaster through the meeting of a hazard with exposed people, infrastructure and unequal capacity to respond. Adaptation can reduce damage; mitigation limits the amount of change that requires adaptation. The distinction is developed in [climate mitigation versus adaptation](/climate-mitigation-vs-adaptation/).

## Where do the ranges come from?

Four sources of uncertainty deserve separate names.

### Scenario uncertainty

Future emissions and land use depend on decisions that have not been made. Scenario uncertainty grows in importance over longer horizons as low- and high-emissions pathways diverge.

### Model uncertainty

Models differ in resolution and in how they approximate clouds, aerosols, vegetation, ice and other processes. An ensemble, meaning a collection of model runs, helps reveal where conclusions are robust and where the spread is wider. Models are not simply counted as equally independent votes; assessments may use observations, model performance and process evidence to constrain results.

### Internal variability

The climate system varies naturally through processes such as El Nino and La Nina and through chaotic atmospheric and ocean behavior. This variability can temporarily amplify or mask a long-term trend, especially over smaller regions and shorter periods. Its precise sequence is largely unpredictable.

The [Fifth National Climate Assessment chapter on Earth-system processes](https://toolkit.climate.gov/NCA5_Ch3_Earth-Systems) explains that internal variability becomes more important as spatial scale decreases. At regional and multidecadal scales, it can contribute more uncertainty than either the model or the scenario for some variables.

### Observational and downscaling uncertainty

Observations used to evaluate models have measurement coverage and error. Translating a coarse global projection to a county, river basin or street adds further methodological choices. Statistical and dynamical downscaling can provide useful local detail, but a finer-looking map is not automatically a more certain map.

The Met Office's [explanation of projection uncertainty](https://www.metoffice.gov.uk/research/climate/understanding-climate/seamless-prediction) identifies internal variability, observational uncertainty, emissions uncertainty and modelling uncertainty, and explains why ensembles are used to explore a range rather than advertise one immaculate line.

## What do confidence and likelihood mean in an assessment?

In assessment reports, **confidence** and **likelihood** are not synonyms. Confidence describes the strength, quality and consistency of the evidence and the degree of agreement. Likelihood is a probabilistic judgment about an outcome.

The [Fifth National Climate Assessment's guide to calibrated language](https://toolkit.climate.gov/NCA5_Front-Matter) gives the numerical convention behind several familiar terms: "very likely" means a probability from 90% to 100%, "likely" means 66% to 100%, and "as likely as not" means 33% to 66%. These intervals overlap because they are communication categories, not adjacent bins in a spreadsheet.

A high-confidence finding need not include a probability. Conversely, a numerical model range does not automatically establish high confidence in every mechanism behind it. Read the term attached to the exact claim, not as a transferable badge for the whole paragraph.

## How should you read a climate projection chart?

Before interpreting the shape or color, check seven items:

1. **Variable:** Is it temperature, rainfall, sea level, soil moisture or a hazard index?
2. **Baseline:** Relative to which years is change measured?
3. **Time window:** Is the point one year, a decade or a 20-year average?
4. **Geographic scale:** Global means are not local forecasts.
5. **Scenario:** Which emissions or forcing pathway supplies the input?
6. **Band:** Does shading show model spread, a likely range, confidence interval or something else?
7. **Processing:** Has the output been bias-adjusted, weighted or downscaled?

Then ask whether the chart shows an absolute value or a change from a reference. Two charts can both be correct while using different baselines, scenarios and averaging periods. Comparing their headline numbers without reconciling those choices manufactures a disagreement that the underlying studies do not have.

For local decisions, use an assessment or climate service designed for that place and variable. A global multimodel mean is appropriate for understanding the direction of planetary warming; it is not a drainage design value or an emergency forecast.

## What is the honest bottom line?

Climate models do not offer one photograph of 2100. They show a set of conditional futures bounded by physical understanding, tested against evidence and widened where knowledge or natural variability demands it.

The robust message is not vague: continued emissions add warming; more warming increases multiple hazards; oceans and ice carry long memory. The open part is consequential: emissions choices strongly affect the late-century range, while adaptation and development affect who is exposed and how much damage follows. Uncertainty belongs in the decision, but it is not evidence that every outcome is equally plausible or that action has no effect.

## Frequently asked questions

**Are climate projections predictions?**

No. A projection describes what models show under stated assumptions, including an emissions pathway. It is conditional on those inputs and on the climate response. A prediction selects an expected outcome; major scenario exercises generally explore alternatives without assigning each scenario a probability.

**Why do climate models give a range instead of one number?**

The range reflects different future emissions pathways, differences in model response, natural climate variability, and observational or downscaling limitations. The relative importance of each source changes with the variable, timescale and geographic scale.

**What parts of future climate change are most certain?**

Continued greenhouse-gas emissions produce additional warming, heat extremes increase as warming rises, and ocean and ice responses drive long-lived sea-level change. Exact local outcomes, especially precipitation and the sequence of individual events, generally carry more uncertainty.

**Does uncertainty mean climate models are unreliable?**

No. A stated uncertainty range is part of the result. Models are evaluated against observations and past climate, compared across research groups, and combined with physical understanding and other evidence. Reliability depends on the variable and scale, so a global temperature projection can be stronger than a local rainfall estimate.

**What should I check on a climate projection chart?**

Check the variable, reference baseline, time window, geographic scale, emissions scenario, meaning of any shaded range, and whether data were weighted or downscaled. Compare numbers only after confirming that these choices match.


---

# Climate Mitigation vs. Adaptation: Why We Need Both

> Climate mitigation limits future change by reducing greenhouse-gas emissions or increasing durable removals. Climate adaptation reduces harm by changing buildings, infrastructure, ecosystems, services, or behavior for current and expected conditions. Both are necessary: adaptation protects people from impacts already occurring, while mitigation prevents the climate hazard from growing beyond what communities and ecosystems can reasonably adapt to.

Source: https://climateofourfuture.org/climate-mitigation-vs-adaptation/  
Publisher: Climate in Plain Sight  
Published: 2026-07-19  
Updated: 2026-08-25

## Mitigation limits change; adaptation limits harm

Climate mitigation reduces the greenhouse-gas emissions causing climate change or increases durable removals from the atmosphere. Climate adaptation changes human or natural systems to reduce harm from climate effects that are occurring or expected. Replacing fossil-fuel power with low-carbon electricity is mitigation; redesigning a neighborhood to withstand hotter summers and heavier rain is adaptation.

We need both. Adaptation protects people now and during future changes that cannot be entirely avoided. Mitigation determines how much additional warming and associated risk the world must eventually handle. Choosing between them is like debating whether a leaking boat needs both a patched hull and a bucket. The answer becomes clearer around the ankles.

## The difference at a glance

| Feature | Mitigation | Adaptation |
|---|---|---|
| Primary goal | Limit the magnitude of climate change | Reduce damage and improve resilience |
| Acts on | Greenhouse-gas sources and sinks | Exposure, vulnerability, and local systems |
| Benefit scale | Often global, with local co-benefits | Often local or regional, sometimes wider |
| Time horizon | Benefits grow as warming is avoided | Can provide immediate and long-term protection |
| Examples | Clean electricity, efficiency, methane cuts, forest protection | Heat plans, flood design, water conservation, climate-ready crops |
| Main limit | Requires broad, sustained emissions change | Becomes harder and costlier as climate hazards intensify |

The categories sometimes overlap. Urban trees can shade neighborhoods, reducing heat exposure, while also storing some carbon. Better building efficiency lowers emissions and helps residents maintain safer indoor temperatures during heat. These “both” benefits are valuable, but they should be measured honestly rather than used to make every project sound like a climate Swiss Army knife.

## What counts as climate mitigation?

Mitigation intervenes in the causes of human-driven warming. Major approaches include:

- Producing electricity with low-carbon sources
- Electrifying vehicles, heating, and industrial processes where suitable
- Improving energy and material efficiency
- Cutting methane leaks and other non-carbon-dioxide emissions
- Reducing deforestation and degradation of carbon-rich ecosystems
- Changing industrial processes and product demand
- Removing carbon dioxide durably to balance hard-to-eliminate residual emissions

The [greenhouse effect explainer](/greenhouse-effect-explained/) shows why emissions reductions matter physically. Carbon dioxide accumulates, so total cumulative emissions largely determine long-term warming. Deep, sustained cuts reduce the amount added; reaching net-zero carbon-dioxide emissions stops additional CO2-driven warming from accumulating.

“Net zero” does not mean every source disappears or that emissions cease to matter. It means remaining human-caused emissions are balanced by removals. The smaller the residual emissions, the less removal is needed. Removal methods differ in permanence, land demand, cost, measurement, and ecological effects, so an accounting label is not enough.

## What counts as climate adaptation?

Adaptation adjusts systems to actual or expected climate conditions. Examples include:

- Heat-health warnings, cooling access, shade, and reflective roofs
- Floodplain restoration, drainage upgrades, barriers, and safer building locations
- Water conservation, reuse, storage, and drought planning
- Crop choices, soil practices, and planting schedules suited to changing conditions
- Coastal buffers, elevated structures, and planned relocation where risk becomes unacceptable
- Healthcare surveillance and emergency planning for climate-sensitive risks
- Protecting habitat connections so species can move and ecosystems can recover

Good adaptation starts with a specific hazard, exposed population or asset, and decision. “Become resilient” is a nice sentiment and a terrible procurement specification. A city should know whether it is reducing indoor heat, flash flooding, water shortage, smoke exposure, or several measured risks.

Adaptation also needs maintenance. A warning system must reach people in languages and formats they can use. A flood barrier must be inspected. Trees require water and years to mature. A cooling center is of limited help if transport is unavailable or residents fear leaving pets behind.

## Why mitigation cannot replace adaptation

Even rapid emissions cuts cannot instantly reverse every climate change. The world has already warmed, sea level responds over long periods, and communities face present-day heat, fire weather, flooding, and water stress. Infrastructure built today may operate for decades.

Adaptation reduces current vulnerability while preparing for plausible future conditions. Better heat alerts can save lives during the next event, before global mitigation has had time to alter the trajectory substantially. Updated engineering standards can prevent new buildings from locking in yesterday's assumptions.

The IPCC's [impacts and adaptation headline findings](https://www.ipcc.ch/report/ar6/wg2/resources/spm-headline-statements/) conclude that some adaptation has reduced vulnerability, while limits have already been reached in some contexts. Adaptation is therefore essential but not infinitely elastic.

## Why adaptation cannot replace mitigation

Adaptation becomes more difficult as warming and associated hazards increase. A seawall can reduce flood risk up to its design conditions; it cannot command the ocean to respect the planning memo. Crops can be changed, but heat and water limits still exist. Ecosystems may lose species or functions beyond thresholds that management cannot readily restore.

Without mitigation, communities must keep adapting to a moving target. Costs rise, options narrow, and some losses become irreversible. Low-income communities and countries with fewer resources often face high vulnerability despite contributing less to historical emissions, making finance and fairness central rather than decorative concerns.

Mitigation reduces the size of the adaptation challenge for everyone. It cannot eliminate all damage, but every increment of warming avoided reduces some risks.

## How the same project can do both—or cause conflict

Some actions create aligned benefits:

### Efficient, well-designed buildings

Insulation, shading, ventilation, efficient equipment, and clean electricity can reduce emissions while making indoor conditions safer and more affordable. Design must suit the local climate; measures that help in a cool, dry region may need modification in a hot, humid one.

### Urban greenery

Trees and vegetation can shade streets, cool through evapotranspiration, manage some stormwater, support biodiversity, and store carbon. Poor species choice, inadequate maintenance, water scarcity, allergens, or roots conflicting with infrastructure can reduce benefits. Planting is the opening scene, not the closing credits.

### Wetland and forest protection

Healthy ecosystems can store carbon and buffer floods, heat, erosion, or storm surge. But carbon goals should not displace local communities, erase Indigenous rights, or justify ecologically inappropriate plantations. Protecting a diverse existing ecosystem is not equivalent to counting rows of one fast-growing tree.

Other actions create tradeoffs. Energy-intensive air conditioning protects against heat but can increase emissions if electricity is carbon-intensive and equipment inefficient. A concrete flood structure may carry high embodied emissions or shift water toward another neighborhood. Bioenergy or tree planting can compete with food production, biodiversity, or land rights.

The answer is not to reject action whenever tradeoffs exist. It is to assess the full system and avoid solving one risk by quietly mailing another to somebody else.

## A household example

Consider a home facing hotter summers.

**Adaptation measures** might include exterior shade, safe nighttime ventilation where climate and security allow, an efficient cooling system, a heat pump, backup plans for power outages, and checking on vulnerable neighbors.

**Mitigation measures** might include energy efficiency, clean electricity, electrified heating and cooking, reduced vehicle fuel use, and supporting wider infrastructure or policy change.

One appliance can serve both goals: an efficient heat pump may reduce fossil-fuel use and provide cooling. But whether it lowers emissions depends on the previous equipment, electricity supply, building, installation, and use. Whether it protects during an outage depends on backup power and building performance. Climate action rarely fits on the side of a cereal box.

Households should use qualified local professionals for electrical, structural, and major heating or cooling work, and follow current public-health guidance during hazards.

## A city example

A city facing heavier rainfall can combine:

- Emissions cuts from transport, buildings, electricity, and waste
- Updated rainfall assumptions in infrastructure design
- Permeable surfaces, parks, wetlands, and detention areas
- Drainage maintenance and flood-warning systems
- Restrictions on new development in high-risk areas
- Financial help for residents who cannot afford protective upgrades

The rainfall hazard connects to [climate change and extreme weather](/climate-change-extreme-weather/), but disaster risk also depends on exposure and vulnerability. A drainage project that protects a business district while increasing flooding downstream is not equitable adaptation. A transit policy that cuts emissions but becomes unaffordable to low-income riders is not a durable success.

## How to evaluate a climate action

Ask seven questions before accepting a project label:

1. **What problem does it address?** Name the emissions source or climate hazard.
2. **How large and durable is the benefit?** Avoid counting temporary or easily reversed gains as permanent.
3. **Compared with what baseline?** A claim needs a credible alternative scenario.
4. **Who controls implementation?** Household advice cannot substitute for utility, city, or national decisions.
5. **Who benefits and who bears costs?** Include renters, workers, future residents, and affected communities.
6. **Could it create maladaptation?** An action may lock in new exposure, emissions, or inequality.
7. **How will results be monitored?** Plans need measurable outcomes and revision.

**Maladaptation** means an intervention unintentionally increases climate vulnerability, greenhouse-gas emissions, or inequity. Examples might include encouraging development behind a protective structure without planning for its limits, or expanding cooling in a way that overloads an unreliable grid during peak heat.

## Individual choices and systems change

Individuals make meaningful decisions as residents, workers, voters, customers, investors, and community members. Household efficiency or lower-emission transport can cut personal emissions and demonstrate demand. Emergency plans and home upgrades can reduce risk.

Yet electricity grids, transit networks, building codes, industrial supply chains, land-use rules, and public finance shape the choices available. Telling every renter to install equipment they do not own is not a strategy. Effective climate action aligns individual options with institutional and policy change.

Avoid purity tests. An action does not need to solve the entire problem to be useful, but its scope should be stated honestly. Likewise, a small personal action does not cancel the need for large emitters and governments to act at scale.

## A practical order of operations

For a household, organization, or city:

1. Measure major emissions sources and climate hazards.
2. Protect people from immediate, severe risks.
3. Avoid new high-emission or high-exposure lock-in.
4. Cut emissions with proven, durable measures.
5. Adapt infrastructure and services for current and plausible future conditions.
6. Monitor results, distributional effects, and unintended consequences.
7. Update the plan as science, technology, and local conditions change.

This sequence is not universally rigid. Emergency adaptation may leap to the front, and long-lived investments require early mitigation decisions. It does keep “action” connected to actual outcomes.

Mitigation and adaptation are ultimately two views of the same future. Mitigation asks how much change can still be limited. Adaptation asks how people and ecosystems can live more safely with the change that occurs. A serious climate response keeps both questions open—and keeps checking who gets to answer them.

## Frequently asked questions

**What is an example of climate mitigation?**

Replacing fossil-fuel electricity with low-carbon generation is mitigation because it reduces the emissions driving warming. Other examples include energy efficiency, electrifying vehicles and heating where appropriate, cutting methane leaks, protecting carbon-rich ecosystems, changing industrial processes, and using durable carbon removal for residual emissions that are difficult to eliminate.

**What is an example of climate adaptation?**

A heat-health plan is adaptation because it reduces harm from hotter conditions through warnings, cooling access, outreach, and emergency response. Other examples include improved drainage, water conservation, climate-ready building standards, coastal buffers, crop changes, and relocating development away from risks that cannot be managed safely.

**Why is adaptation not enough by itself?**

Adaptation has physical, ecological, financial, and social limits. As warming increases, hazards intensify and a successful measure may be overtaken by conditions beyond its design. Some losses cannot be reversed. Mitigation reduces the amount of future change, preventing the adaptation challenge from becoming continually larger and more expensive.

**Why is mitigation not enough by itself?**

Climate impacts are already occurring, and some further change cannot be avoided immediately even with rapid emissions cuts. People, infrastructure, and ecosystems need protection now. Heat plans, flood preparation, water management, and resilient design reduce current harm while mitigation changes the longer-term trajectory. Waiting for emissions cuts alone leaves existing vulnerability unaddressed.

**Can one climate action provide both mitigation and adaptation?**

Yes. A well-insulated, shaded, efficiently electrified building can reduce energy emissions while protecting occupants during heat. Urban trees may store carbon, provide shade, and manage stormwater. Benefits depend on design, maintenance, local climate, energy supply, and equity, so each mitigation and adaptation claim should be assessed separately.

**What is maladaptation?**

Maladaptation is an action intended to address climate risk that instead increases vulnerability, emissions, or inequality. A flood barrier might encourage unsafe development behind it or shift water toward another community. Evaluating who benefits, who bears new risks, how long protection lasts, and what happens under conditions beyond the design helps identify maladaptation.


---

# Climate Scenarios Explained: Reading SSP Labels

> Climate scenarios describe possible futures under stated assumptions, not forecasts of which future will occur. Shared Socioeconomic Pathway labels combine a societal storyline with an approximate radiative-forcing level in 2100. In SSP2-4.5, the 2 identifies the storyline and 4.5 denotes watts per square metre, not degrees of warming. Read the complete label alongside the chart's variable, baseline and time window; neither the highest scenario nor the middle one is automatically the expected outcome.

Source: https://climateofourfuture.org/climate-scenarios-ssp-pathways-explained/  
Publisher: Climate in Plain Sight  
Published: 2026-09-08  
Updated: 2026-09-08

## What do climate scenarios actually describe?

Climate scenarios describe possible futures under stated assumptions, not forecasts of which future will occur. Shared Socioeconomic Pathway labels combine a societal storyline with an approximate radiative-forcing level in 2100. In SSP2-4.5, the 2 identifies the storyline and 4.5 denotes watts per square metre, not degrees of warming. Read the complete label alongside the chart's variable, baseline and time window; neither the highest scenario nor the middle one is automatically the expected outcome.

This guide decodes the labels used in the Intergovernmental Panel on Climate Change's Sixth Assessment Report, or IPCC AR6. It does not run a climate model or update the probability of today's policy outcomes.

## How is a scenario different from a projection?

A scenario supplies assumptions about how conditions develop. A projection describes a response conditional on those assumptions and on the model or assessment method.

The US Fifth National Climate Assessment gives examples of scenario inputs: emissions, population, energy and land use. It explicitly distinguishes climate projections from forecasts or predictions. Future choices and the climate system's response both matter. [NCA5 scenarios appendix](https://toolkit.climate.gov/sites/default/files/2025-07/NCA5_App3_Scenarios-and-Datasets.pdf)

Consider the statement “under SSP2-4.5, this assessment projects a change.” The words “under SSP2-4.5” are part of the claim. Removing them does not simplify the same result; it changes a conditional statement into an unconditional one.

For the broader process, including models and assessment ranges, see our [climate-projections guide](/climate-future-what-models-project/).

## What do the two parts of an SSP label mean?

SSP stands for **Shared Socioeconomic Pathway**. The storyline describes a possible societal development path, including factors such as population, economic development and urbanization. Researchers can combine a storyline with different mitigation assumptions; the storyline number alone does not specify the resulting emissions.

The five families are broadly described as sustainability (SSP1), middle-of-the-road development (SSP2), regional rivalry (SSP3), inequality (SSP4) and fossil-fuel-intensive development (SSP5). These are scenario descriptions, not rankings of countries. [IPCC Chapter 1, section 1.6.1.1](https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-1/)

The suffix describes the approximate radiative-forcing level resulting in 2100. **Radiative forcing** measures a change in Earth's energy balance, expressed in watts per square metre, written W/m². It is different from the resulting temperature change.

The IPCC's own label definition calls the forcing level approximate. A label is not a promise that every climate model calculates exactly that forcing. [IPCC Summary for Policymakers, footnote 22](https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/)

## How do the familiar labels compare?

The five illustrative scenarios used extensively in AR6's physical-science assessment are:

| Complete label | Societal family | Nominal forcing level in 2100 |
|---|---|---:|
| SSP1-1.9 | SSP1 | 1.9 W/m² |
| SSP1-2.6 | SSP1 | 2.6 W/m² |
| SSP2-4.5 | SSP2 | 4.5 W/m² |
| SSP3-7.0 | SSP3 | 7.0 W/m² |
| SSP5-8.5 | SSP5 | 8.5 W/m² |

These are forcing categories relative to pre-industrial conditions, not extra warming from today. IPCC radiative-forcing assessments commonly use 1750 as their reference; a temperature chart may instead use 1850–1900. Record the reference for the quantity actually plotted.

Read the first two rows together: one societal family appears with two forcing levels. That alone shows why “SSP1” is incomplete when identifying a climate-model experiment. Read the third and fifth rows together: both the family and forcing label change, so the comparison is not an experiment in changing only one policy.

The IPCC describes SSP2-4.5 as intermediate emissions and SSP5-8.5 as very high emissions within this illustrative set. Neither name supplies a probability. [IPCC scenario overview, Box SPM.1](https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/)

## Is the highest scenario the worst-case forecast?

No. The IPCC attaches no likelihood to the scenarios assessed in its physical-science report. Their presence in a figure does not mean equal odds, and a central-looking line is not automatically a median forecast.

A high scenario can help investigate consequential conditions without being selected as the expected future. Conversely, choosing a low scenario for a chart does not demonstrate that its assumptions will be achieved. Evaluating current policies requires current policy evidence, not a judgment based on a legend's position or color.

Nor does an endpoint describe the entire journey. The original Scenario Model Intercomparison Project design explicitly includes questions about peak-and-decline forcing and long-term outcomes. Two paths need not have the same earlier conditions just because their endpoints look similar. [ScenarioMIP experimental-design paper](https://gmd.copernicus.org/articles/9/3461/2016/)

## Are RCP4.5 and SSP2-4.5 interchangeable?

RCP means **Representative Concentration Pathway**, an earlier scenario framework. The Met Office's UKCP18 guidance explains that RCP names also incorporate forcing targets for 2100 relative to pre-industrial levels. One RCP can be consistent with different socioeconomic assumptions. [Met Office RCP guidance](https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/research/ukcp/ukcp18-guidance---representative-concentration-pathways.pdf)

Matching suffixes do not make old and new datasets identical. IPCC Chapter 1 identifies differences in gas composition, trajectories and effective forcing between SSP and RCP scenarios. A difference between their projected temperatures cannot automatically be attributed only to a change in climate models.

Record the full scenario and dataset generation. Do not silently replace “RCP4.5” with “SSP2-4.5” while keeping another assessment's numbers.

## How can you audit a caption without running a model?

Use this original reading exercise. Imagine a draft caption saying: “SSP2-4.5 predicts 4.5 degrees in 2100.” No dataset accompanies it.

Three checks reveal the problem:

1. **Label check:** 4.5 is the nominal forcing suffix, not a temperature result.
2. **Claim check:** “predicts” discards the conditional character of the projection.
3. **Evidence check:** no variable definition, temperature baseline, averaging period or source result supports the claimed number.

Do not repair it by guessing a different temperature. A defensible replacement is: “SSP2-4.5 identifies the scenario used; the temperature result must be read from the cited assessment with its reference period and uncertainty.”

For a real figure, make a short record:

| Record field | What to copy from the source |
|---|---|
| Scenario | Complete label, including any suffix or variant |
| Data identity | Assessment, dataset version and model generation |
| Quantity | Variable and units, not the units inferred from the scenario |
| Time and reference | Averaging years and baseline years |
| Display meaning | What the line, shading and range actually represent |

The record does not calculate a result. It identifies what is missing before comparing two results.

## Why do versions and warming-level maps matter?

Version information can change the interpretation. IIASA's legacy SSP database documents that its December 2018 release added low scenarios targeting 1.9 W/m² and harmonized emissions with historical inventories. That is a specific historical release, not a claim that its old update notice describes the latest database today. Copy the version associated with the figure you are reading. [IIASA SSP database release notes](https://tntcat.iiasa.ac.at/legacy-sspdb/dsd?Action=htmlpage&page=welcome)

A **global warming level** is another organizing device, not another SSP suffix. A map at 2°C global warming asks about conditions at that warming level rather than identifying one calendar year. The Met Office explains that warming-level comparisons separate the amount of warming from when it is reached; it also cautions that effects such as sea-level rise do not stabilize simply because temperature does. [Met Office projection guide](https://www.metoffice.gov.uk/blog/2023/making-sense-of-climate-change-projections)

This distinction makes comparisons more useful, not less urgent. Read scenarios as conditions to examine, keep evidence about present policies separate, and retain uncertainty where the source places it. For location-specific engineering or emergency decisions, use qualified local professionals and current official guidance. A global scenario label cannot establish whether a particular place is safe.

Our [climate basics section](/climate-basics/) explains the underlying physical terms.

## Sources

- [IPCC AR6 Working Group I: Chapter 1, scenario framework and limitations](https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-1/).
- [IPCC AR6 Working Group I: Summary for Policymakers, Box SPM.1 and footnote 22](https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/).
- [US Fifth National Climate Assessment: Appendix 3, Scenarios and Datasets](https://toolkit.climate.gov/sites/default/files/2025-07/NCA5_App3_Scenarios-and-Datasets.pdf).
- [O'Neill and colleagues: ScenarioMIP experimental design](https://gmd.copernicus.org/articles/9/3461/2016/).
- [Met Office: UKCP18 Representative Concentration Pathways guidance](https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/research/ukcp/ukcp18-guidance---representative-concentration-pathways.pdf).
- [IIASA: SSP database Version 2.0 release notes](https://tntcat.iiasa.ac.at/legacy-sspdb/dsd?Action=htmlpage&page=welcome).
- [Met Office: Making sense of climate change projections](https://www.metoffice.gov.uk/blog/2023/making-sense-of-climate-change-projections).

## Frequently asked questions

**What does SSP2-4.5 mean?**

SSP means Shared Socioeconomic Pathway. The 2 identifies the societal development family; 4.5 identifies an approximate radiative-forcing level of 4.5 watts per square metre in 2100 relative to pre-industrial conditions. It is not 4.5 degrees of warming. Temperature results must come from the specific assessment, with its baseline, time window and uncertainty.

**Are SSP scenarios forecasts?**

No. They describe conditional futures, not a selection of what will happen. Climate projections depend on the stated scenario and the climate system's response. The IPCC physical-science assessment does not assign scenario probabilities, so neither a middle line nor the highest line automatically represents the expected outcome.

**Why are there two SSP1 scenarios in many charts?**

The societal storyline and forcing level are separate parts of the label. SSP1-1.9 and SSP1-2.6 share the SSP1 development family but have different nominal forcing levels in 2100. Specifying only SSP1 therefore does not identify which climate scenario supplied the inputs. Copy the complete label when comparing figures.

**Can I substitute an SSP scenario for an RCP with the same number?**

Do not treat them as identical datasets. RCP and SSP scenarios can share a nominal forcing suffix while differing in their gas mixtures, trajectories and effective forcing. Record the exact scenario, dataset generation, period and baseline before comparing results; a change cannot automatically be attributed solely to newer climate models.

**Does a map at 2 degrees of global warming predict conditions in 2100?**

Not by that description alone. A warming-level map concerns conditions at the specified global warming level rather than one universally fixed year. Check the map's baseline, variables and methodology. For location-specific engineering or emergency decisions, use qualified local professionals and current official guidance; a global scenario label cannot establish local safety.


---

# The Greenhouse Effect Explained Without the Fog

> The greenhouse effect is the process by which gases such as carbon dioxide, methane, and water vapor absorb and re-emit some infrared energy leaving Earth's surface, slowing heat loss to space. The natural effect keeps Earth habitable. Human activities have strengthened it by increasing long-lived greenhouse-gas concentrations, creating an energy imbalance that warms the atmosphere, ocean, and land.

Source: https://climateofourfuture.org/greenhouse-effect-explained/  
Publisher: Climate in Plain Sight  
Published: 2026-07-19  
Updated: 2026-08-25

## The greenhouse effect, in one clear pass

The greenhouse effect is the natural process by which certain atmospheric gases slow Earth's loss of heat to space. Sunlight warms the surface; the surface emits infrared energy; greenhouse gases absorb and re-emit some of that energy, leaving the lower atmosphere and surface warmer than they would otherwise be. Human activities have strengthened this effect by increasing concentrations of carbon dioxide, methane, and other heat-trapping gases.

The natural greenhouse effect is not the villain. Without it, Earth would be far colder. The climate problem is the **enhanced greenhouse effect**: adding gases changes the planet's energy balance, rather like making an insulating layer more effective while the heating system continues to run.

That analogy is useful, but only up to a point. The atmosphere is not a literal glass greenhouse, and greenhouse gases do more than “trap” a fixed packet of heat. They absorb and emit infrared radiation in particular wavelength bands. The result is slower energy loss to space until the climate system warms enough to restore balance.

## The energy journey from Sun to space

Understanding the mechanism takes four steps.

### 1. Solar energy arrives

The Sun sends energy toward Earth mainly as shortwave radiation, including visible light. Some is reflected by clouds, aerosols, ice, and bright surfaces. The rest is absorbed by the atmosphere, land, and ocean.

### 2. The surface warms

Absorbed solar energy warms the surface. A warm surface then emits energy upward as infrared radiation. Infrared is invisible to human eyes, but it carries energy all the same; the universe does not require a visible receipt.

### 3. Greenhouse gases interact with infrared radiation

Molecules such as carbon dioxide, methane, nitrous oxide, and water vapor absorb infrared radiation at particular wavelengths. They then emit infrared energy in different directions. Some goes upward, and some returns toward the lower atmosphere and surface.

### 4. Earth eventually loses energy to space

Energy still escapes. Greenhouse gases do not put a lid on the planet. But increasing their concentration makes the effective path to space less direct and shifts where infrared energy can readily escape. The climate system gains energy until warming increases outgoing energy enough to approach a new balance.

NASA's current [explanation of climate causes](https://science.nasa.gov/climate-change/causes/) describes today's warming as an expansion of the greenhouse effect driven by human activity. The IPCC's Sixth Assessment synthesis goes further on attribution: human activities, principally greenhouse-gas emissions, have unequivocally caused global warming.

## Natural greenhouse effect vs. human enhancement

The distinction is simple but essential.

| Process | What causes it | Role in climate |
|---|---|---|
| Natural greenhouse effect | Naturally present greenhouse gases, clouds, and the water cycle | Keeps Earth warm enough for the climate and ecosystems we know |
| Enhanced greenhouse effect | Human-caused increases in long-lived greenhouse gases and other climate forcings | Adds energy to the climate system and drives current global warming |

Carbon dioxide moves naturally among the atmosphere, ocean, soils, rocks, and living things. Human activities add extra carbon dioxide by burning coal, oil, and gas and by changing land use, including deforestation. The fact that a gas has natural sources does not mean additional human emissions have no effect. Rivers are natural too; adding a hose still raises the pool.

Scientists distinguish the human contribution using multiple lines of evidence: measured atmospheric concentrations, the chemical and isotopic fingerprints of carbon, inventories of fuel use and land-use change, observed patterns of warming, and physical models. Natural influences such as volcanic eruptions and solar variation affect climate, but they do not explain the sustained recent warming pattern.

## The major greenhouse gases play different roles

Calling all greenhouse gases “carbon” hides important differences.

### Carbon dioxide

Carbon dioxide is the largest contributor to human-caused warming over the long term. It is released by fossil-fuel combustion, cement production, and land-use change, among other processes. A portion of emitted carbon dioxide remains in the atmosphere while land and ocean sinks take up another portion. Its climate influence persists across long timescales, which makes cumulative emissions important.

### Methane

Methane absorbs infrared energy efficiently and has a shorter atmospheric lifetime than carbon dioxide, but it contributes substantially to current warming. Human sources include fossil-fuel production and transport, livestock, rice cultivation, and waste. Cutting methane can slow near-term warming, while carbon-dioxide emissions still must reach net zero to stop adding further long-term warming.

### Nitrous oxide

Nitrous oxide is a long-lived greenhouse gas associated with agricultural soils and fertilizer use as well as industrial and combustion sources. It is present at much lower concentration than carbon dioxide, yet each molecule has strong radiative effects.

### Water vapor

Water vapor is the most abundant greenhouse gas, but in current climate change it acts mainly as a **feedback**, not the initial forcing. Warmer air can contain more water vapor; because water vapor itself is a greenhouse gas, that increase amplifies warming. The extra water vapor does not remain independently in the atmosphere if temperature falls, because it condenses and precipitates.

That forcing-feedback distinction matters. Saying “water vapor is a greenhouse gas” is correct. Using that fact to dismiss carbon dioxide as a driver is not.

## Forcing, feedback, and response

These three terms organize much of climate science.

**A forcing** changes Earth's energy balance from outside the climate system's internal response. Rising carbon dioxide from human emissions is a positive forcing because it reduces outgoing energy relative to incoming energy until warming occurs. Large volcanic eruptions can create a temporary negative forcing by adding reflective particles high in the atmosphere.

**A feedback** is a process triggered by climate change that then amplifies or reduces it. Increasing water vapor is a positive feedback. Melting snow and sea ice expose darker surfaces that absorb more sunlight, another positive feedback. Some processes, including greater infrared emission from a warmer Earth, oppose the initial imbalance and are negative feedbacks.

**The response** is the change in temperature, precipitation, circulation, ice, ocean conditions, and ecosystems as the climate system adjusts. Different parts respond on different timescales. The atmosphere changes quickly; deep ocean and large ice sheets carry long memory.

These ideas also explain why a short cold spell does not overturn global warming. Weather can swing while the long-term energy imbalance persists; [weather and climate operate on different scales](/weather-vs-climate/).

## Why a small concentration can have a large effect

Greenhouse gases are trace constituents of the atmosphere, but abundance alone does not determine influence. What matters is whether a molecule interacts with infrared radiation, at which wavelengths, how long it remains, how its concentration changes, and how the climate system responds.

A small amount of an active ingredient can matter enormously. Ozone high in the stratosphere filters harmful ultraviolet radiation even though it is not most of the air. Salt is a small fraction of soup, yet omitting it is not a subtle event. These analogies do not prove greenhouse physics; laboratory spectroscopy and atmospheric observations do. They simply disarm the mistaken premise that “small share” means “no effect.”

Carbon dioxide's absorption is also not so completely “saturated” that adding more has no influence. Absorption varies across wavelength bands and atmospheric height. Increasing concentration broadens the effective absorption range and raises the altitude from which energy readily escapes to space. Because higher layers are generally colder in the relevant part of the atmosphere, less energy initially escapes; the lower system warms in response.

## What scientists measure

The greenhouse effect is not inferred from surface thermometers alone. Scientists observe:

- Greenhouse-gas concentrations in air and ancient air trapped in ice
- Incoming solar and outgoing infrared radiation
- Spectral patterns showing which wavelengths gases absorb
- Temperature changes through the atmosphere and ocean
- Ocean heat content, ice loss, sea-level change, and ecosystem responses
- Carbon isotopes and declining atmospheric oxygen consistent with fossil-fuel combustion

No single measurement carries the whole case. The conclusion rests on converging physics and observations. This is why the IPCC can state human causation with high confidence rather than treating it as a guess produced by one computer model.

## Does the ozone hole cause global warming?

No. Ozone depletion and climate change are different problems with some interactions. Stratospheric ozone protects life from much ultraviolet radiation; greenhouse gases change Earth's energy balance. Certain industrial chemicals have contributed to both ozone depletion and warming, but the ozone hole is not the principal cause of current climate change.

The successful international response to ozone-depleting substances is still relevant as a policy lesson: coordinated rules can change global emissions. It is not evidence that the climate problem has already been solved by the same mechanism.

## From mechanism to impacts

Extra energy does not appear only as a smooth increase in air temperature. Most of the climate system's excess heat accumulates in the ocean. Warming also changes evaporation, atmospheric moisture, circulation, ice, and sea level. Those shifts alter the conditions in which extremes occur.

That does not mean climate change “causes” every individual flood, drought, fire, or storm in a simple on-off sense. Attribution studies ask how human influence changed an event's likelihood or intensity relative to a world without that influence. The evidence and confidence vary by hazard and region, as the guide to [climate change and extreme weather](/climate-change-extreme-weather/) explains.

## What stops additional warming?

To halt the continuing rise in human-caused global temperature, net carbon-dioxide emissions must fall to zero, while strong reductions in other greenhouse gases also limit peak warming. “Net zero” means remaining human emissions are balanced by durable removals; it is not a spell that makes past emissions vanish.

Reducing emissions addresses the cause, which is climate mitigation. Preparing homes, cities, agriculture, health systems, and ecosystems for changing conditions is adaptation. Both are necessary, but only mitigation limits how much additional climate change society must adapt to. The distinction is unpacked in [climate mitigation versus adaptation](/climate-mitigation-vs-adaptation/).

The greenhouse effect is therefore neither hoax nor apocalypse machine. It is well-understood atmospheric physics. The natural version makes Earth habitable; human emissions have strengthened it; and the amount of future warming depends substantially on the emissions choices societies make from here.

## Frequently asked questions

**Is the greenhouse effect natural?**

Yes. Naturally occurring greenhouse gases keep Earth's surface much warmer than it would be without them. The current climate problem is the enhanced greenhouse effect: human activities, especially fossil-fuel use and land-use change, have raised concentrations of heat-trapping gases and added warming beyond the natural background.

**How do greenhouse gases warm the planet?**

Earth's warm surface emits infrared energy. Greenhouse-gas molecules absorb infrared radiation at particular wavelengths and emit it in different directions, slowing the net loss of energy to space. The climate system then warms until increased outgoing energy moves it toward a new balance with incoming solar energy.

**If water vapor is the main greenhouse gas, why focus on carbon dioxide?**

Water vapor mainly amplifies temperature change as a feedback: warmer air supports more vapor, which adds warming, while cooling causes vapor to condense. Carbon dioxide can accumulate from human emissions and initiate long-lasting warming. That warming increases water vapor, so the gases have different roles rather than competing explanations.

**Are greenhouse gases too scarce to affect climate?**

No. A gas's effect depends on how it interacts with radiation, its concentration change, lifetime, and atmospheric setting—not simply its percentage of the air. Laboratory spectroscopy, satellite measurements, surface observations, and atmospheric profiles all show the infrared influence of greenhouse gases and the energy imbalance associated with rising concentrations.

**Does the ozone hole cause the greenhouse effect?**

No. Stratospheric ozone depletion and human-caused global warming are distinct problems, though some chemicals and atmospheric processes connect them. Ozone blocks much harmful ultraviolet radiation. Greenhouse gases slow infrared heat loss. Ozone depletion is not the principal cause of the sustained modern warming trend.

**Can the greenhouse effect be reversed?**

The natural greenhouse effect should not be removed; it is essential to Earth's habitable climate. Human-caused warming can be limited by rapidly reducing greenhouse-gas emissions. Reaching net-zero carbon-dioxide emissions stops additional CO2-driven warming from accumulating, while reductions in methane and other gases further limit peak warming.


---

# How Does Climate Change Raise Sea Level?

> Climate change raises global sea level mainly because seawater expands as it warms and because melting glaciers and ice sheets on land add water to the ocean. Local relative sea level can differ from the global average as land rises or sinks and as currents, winds and gravity redistribute water. Tides, waves and storm surge then occur on top of that changing baseline.

Source: https://climateofourfuture.org/how-climate-change-raises-sea-level/  
Publisher: Climate in Plain Sight  
Published: 2026-09-04  
Updated: 2026-09-07

## The short answer

Climate change raises global sea level mainly in two ways: ocean water expands as it warms, and melting glaciers and ice sheets on land add water to the ocean. The global average is not the waterline any one coast will experience. Ocean circulation, gravity, the movement of Earth's crust and local land subsidence or uplift can raise or lower relative sea level at a particular place. Tides, waves and storm surge then act on top of that shifting baseline.

That distinction—global mean versus local relative sea level—keeps a simple physical story from becoming a misleading local forecast.

## What does “sea level” actually mean?

The ocean is not a still basin with one flat, fixed surface. Gravity, winds, currents, water temperature and salinity produce slopes and bulges. Tides move the surface over hours; weather can push water toward or away from a coast; longer-lived changes alter averages over years and decades.

**Global mean sea level** is the average height of the ocean surface across the planet, measured relative to a reference framework tied to Earth. It is useful for tracking changes in the total volume and distribution of ocean water.

**Relative sea level** is the height of the sea compared with the land at a particular coast. A tide gauge measures this relationship directly. If the sea rises while the land stays still, relative sea level rises. If the ocean stays at the same height while the land sinks, relative sea level also rises. People, roads and buildings experience the relative measure.

NOAA therefore cautions that local and global trends are different measurements. A global curve answers a planetary question; a local planning product must account for the coast itself.

## How does warming water raise sea level?

Most substances expand when warmed. Seawater is no exception: added heat changes its density, so the same mass occupies more volume. This contribution is called **thermal expansion**, or sometimes **thermosteric sea-level rise**.

The ocean has absorbed most of the excess heat accumulating in the climate system. Warming is not uniform with depth or location, so thermal expansion is not uniform either. Currents redistribute heat, salt and water, producing regional differences around the global trend.

The mechanism does not require the ocean to boil, or even to look different at the surface. A small density change integrated through an immense volume of seawater changes the height of the ocean. The [greenhouse effect](/greenhouse-effect-explained/) supplies the energy imbalance; the ocean stores much of the added heat; expansion is one physical response.

The IPCC assessed thermal expansion as half of observed global mean sea-level rise over 1971–2018. That fraction belongs to that period. Contributions change over time, so it should not be silently reused as a timeless split.

## How does land ice add water to the ocean?

Glaciers and the Greenland and Antarctic ice sheets store water on land. When they lose mass and that water reaches the ocean, the ocean gains water it did not previously contain.

Ice can be lost through surface melting and runoff, or through faster flow of glaciers into the sea. An iceberg that calves from a glacier is part of the mass transfer even if it melts later. The accounting question is whether the ice was supported by land before entering the ocean.

This is why **land ice** and **sea ice** must not be treated as interchangeable. Sea ice is frozen seawater already floating in the ocean and already displacing nearly its own weight. Its melting has no significant direct effect on sea level. Sea-ice loss still matters for climate because darker ocean absorbs more sunlight than reflective ice, and changes around ice shelves can affect the flow of land-based glaciers.

An ice shelf also mostly floats, so its direct breakup adds little to sea level. But an ice shelf can restrain glaciers behind it. If that restraint weakens and land ice flows into the ocean faster, sea level rises. “Floating ice does not directly add much” is therefore accurate but incomplete without the connection to land ice.

For 2006–2018, the IPCC found that ice-sheet and glacier mass loss together had become the dominant contribution to global mean sea-level rise. Again, the time period matters: the relative shares are not fixed.

## Are there other contributors?

Yes. Water also moves between land and ocean through rainfall, snow, rivers, groundwater, reservoirs and extraction from aquifers. Some land-water changes store more water on continents; others transfer it to the sea. The IPCC's sea-level budget includes changes in land-water storage alongside thermal expansion, glaciers and ice sheets.

The phrase **sea-level budget** means accounting for measured change by adding independently estimated contributions. Ocean-temperature measurements inform thermal expansion. Satellite gravity and ice measurements help estimate changes in water mass. Comparing the sum with observed sea-surface change is an important consistency check.

These additional terms matter scientifically, but they do not overturn the central explanation: present global rise is driven primarily by warming ocean water and loss of land ice.

## Why can sea level rise faster—or fall—at one coast?

Relative sea level reflects several processes at once.

**Vertical land motion.** Deltas can subside as sediments compact. Groundwater or fossil-fuel extraction can contribute to subsidence in some places. Tectonic motion can lift or lower a coast. Land once pressed down by large ice sheets can continue rebounding upward long after the ice disappears, while surrounding regions adjust downward.

**Ocean circulation and winds.** Currents and persistent wind patterns redistribute water. Changes in ocean temperature and salinity alter density and height. These effects can make a regional trend differ from the global mean.

**Gravity, rotation and deformation.** A large ice sheet attracts ocean water through gravity and presses on the solid Earth. When it loses mass, the gravitational field and Earth's shape and rotation adjust. Sea-level change is therefore not a uniform layer spread over a rigid sphere. Different ice-loss sources leave different regional “fingerprints.”

**Short-term water levels.** Tides, waves, storm surge and climate patterns such as El Niño vary around the long-term mean. They are not the same as sea-level rise, but a higher baseline allows a given tide or surge to reach farther or flood more often.

This is also why a location close to a melting ice sheet can see less rise from that ice source than a distant coast: the loss of gravitational attraction and land uplift near the ice partly offset the added water there.

## How do scientists measure sea-level change?

No single instrument supplies the whole record.

**Tide gauges** continuously measure water height relative to a local datum, or reference level. Their great strength is duration: some records extend back more than a century. Because the instrument is attached to land, its trend includes both ocean change and vertical land motion unless combined with geodetic measurements.

**Satellite altimeters** send radar pulses toward the sea surface and measure the return time. With precise knowledge of the satellite's orbit and corrections for the atmosphere, waves and other effects, repeated passes map sea-surface height over most of the global ocean. The continuous satellite-altimetry record begins in the early 1990s.

Tide gauges and satellites are complementary. NOAA uses offshore tide stations to validate and connect satellite measurements, while satellite coverage supplies a nearly global view that sparse coastal stations cannot.

Other observing systems help explain the cause. Argo profiling floats measure ocean temperature and salinity, supporting estimates of heat-driven expansion. The GRACE and GRACE Follow-On satellite missions detect changes in Earth's gravity associated with moving mass, including ice and water. Satellite and airborne measurements track glacier and ice-sheet height and flow.

Agreement among the observed total, thermal expansion and mass additions strengthens the sea-level budget. Measurement uncertainty remains and is reported; it is not resolved by choosing whichever instrument produces the most convenient line.

## Why do projections come as scenarios and ranges?

Future sea level depends on future greenhouse-gas emissions, how much heat the ocean absorbs, how glaciers and ice sheets respond, and how local land and circulation change. Some processes unfold slowly and continue after atmospheric temperatures stabilize. Ice-sheet responses also carry low-probability, high-impact possibilities that are difficult to narrow.

Scientific assessments therefore report ranges under specified emissions scenarios and levels of confidence. A scenario is not a forecast that society will follow that path. A global range is not a parcel-level flood depth. Converting a global projection into local relative sea level requires regional ocean dynamics, land motion and ice-loss fingerprints; converting that into flood risk also requires tides, surge, waves, elevation and protective infrastructure.

## How should a reader use local sea-level information?

Use current products from the authority responsible for the location and decision. Check the scenario, baseline, time horizon, vertical datum and whether the display shows mean sea level, high-tide flooding, storm surge or another quantity. These are not interchangeable layers.

For property, infrastructure, evacuation or emergency decisions, use official local flood maps, forecasts and instructions from emergency managers and coastal agencies. This explainer does not identify safe routes or determine whether a particular site will flood. During an active coastal flood, storm or tsunami warning, follow the current instructions of local authorities.

Sea-level rise is a climate impact; reducing its long-term cause and preparing for the change are different tasks. The distinction between those responses is developed in [climate mitigation versus adaptation](/climate-mitigation-vs-adaptation/), while [climate change and extreme weather](/climate-change-extreme-weather/) explains how a changing baseline alters risk without assigning every event to one cause.

## Sources

- [NASA Science: Sea Level Earth Indicator](https://science.nasa.gov/earth/explore/earth-indicators/sea-leve/)
- [NOAA Ocean Service: Local Sea Level and Global Sea Level](https://oceanservice.noaa.gov/facts/sealevel-global-local.html)
- [NOAA Ocean Service: Satellites and Tide Stations, Working Together](https://oceanservice.noaa.gov/news/feb16/satellites-tide-stations.html)
- [IPCC AR6 Working Group I: Summary for Policymakers](https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/)
- [U.S. Fifth National Climate Assessment: Earth Systems Processes](https://toolkit.climate.gov/NCA5_Ch3_Earth-Systems)

## Frequently asked questions

**What are the two main causes of sea-level rise?**

The two main causes are thermal expansion, in which warming seawater occupies more volume, and loss of land ice, in which water from glaciers and ice sheets enters the ocean. Their relative contributions change over time.

**Does melting sea ice raise sea level?**

Melting floating sea ice has no significant direct effect because it already displaces nearly its own weight in ocean water. Sea-ice loss still affects climate and can indirectly influence land-ice flow through changes around ice shelves.

**Why is local sea-level rise different from the global average?**

Local relative sea level includes ocean warming and circulation, vertical land motion, gravitational and rotational changes from moving ice and water, and short-term tides and weather. A global average cannot substitute for a location-specific assessment.

**How is sea-level rise measured?**

Tide gauges measure water height relative to land at specific coasts, while satellite altimeters map sea-surface height across most of the ocean. Argo floats, satellite gravity missions and ice observations help identify the contributions to the measured change.

**Can sea level fall in some places while the global average rises?**

Yes. Rapid land uplift, changes in currents or the gravitational response to nearby ice loss can offset the global rise at some locations. People experience relative sea level, so the motion of the land matters alongside the ocean.

**Can a global sea-level projection tell me whether a property will flood?**

No. Property-scale risk also depends on local land elevation and motion, tides, storm surge, waves, drainage and protective infrastructure. Use current official local maps and agency guidance for planning, and follow local emergency instructions during an active hazard.


---

# Keeling Curve Explained: Reading the CO2 Record

> The Keeling Curve records atmospheric carbon dioxide measured at Mauna Loa, Hawaii, beginning in 1958. Its repeating seasonal rise and fall sits on a long-term increase. It measures carbon dioxide abundance, not temperature or annual emissions. Understanding the graph means separating those quantities, identifying the observing programme and reading the data notes. The evidence for human causation extends beyond the curve's shape to carbon accounting and chemical measurements.

Source: https://climateofourfuture.org/keeling-curve-explained/  
Publisher: Climate in Plain Sight  
Published: 2026-09-09  
Updated: 2026-09-09

## What does the Keeling Curve show?

The Keeling Curve records atmospheric carbon dioxide measured at Mauna Loa, Hawaii, beginning in 1958. Its repeating seasonal rise and fall sits on a long-term increase. It measures carbon dioxide abundance, not temperature or annual emissions. Understanding the graph means separating those quantities, identifying the observing programme and reading the data notes. The evidence for human causation extends beyond the curve's shape to carbon accounting and chemical measurements.

A familiar graph can conceal several different questions. Why does the line dip? Why measure near a volcano? Does the number describe the whole planet? Answering each requires knowing what was measured before deciding what the result means.

## Who started the record, and which dataset are you reading?

Charles David Keeling began the Mauna Loa measurements in March 1958. Scripps' [history of the record](https://keelingcurve.ucsd.edu/2013/04/03/the-history-of-the-keeling-curve/) describes the early discovery of both the seasonal cycle and an increase between years. Earlier measurements at other locations had helped him distinguish broadly representative air from local influences.

Scripps and the National Oceanic and Atmospheric Administration, or NOAA, operate separate measurement programmes. NOAA's [Mauna Loa trends page](https://gml.noaa.gov/ccgg/trends/) says its measurements began in May 1974, running alongside Scripps' observations. Its full-record graph combines Scripps and NOAA data.

Therefore, record the provider as well as the place. “Mauna Loa” identifies a location; it does not, by itself, identify the data series, processing or release. Do not silently attach a Scripps caption to values taken from NOAA.

## What does ppm mean?

**Parts per million**, abbreviated ppm, expresses a proportion. For atmospheric carbon dioxide reporting, **dry-air mole fraction** means the number of carbon dioxide molecules divided by the total number of air molecules after excluding water vapour.

An illustrative value of **400 ppm** means 400 carbon dioxide molecules per million dry-air molecules, or **0.04%**. It is an explanation of units, not a current reading. NOAA's [global data page](https://gml.noaa.gov/ccgg/trends/global.html) defines this convention.

A ppm value is not tonnes emitted that year. Emissions describe a flow into the atmosphere; atmospheric abundance reflects additions and removals over time. Nor is ppm a temperature unit. The [greenhouse-effect explainer](/greenhouse-effect-explained/) supplies the physical connection between added greenhouse gases and Earth's energy balance.

## Why is Mauna Loa useful, and how is air measured?

NOAA's [measurement-method description](https://gml.noaa.gov/ccgg/about/co2_measurements.html), updated in September 2020, explains that the high-elevation site samples air representative of large areas. Researchers seek background air, meaning air whose composition is not dominated by nearby additions or removals.

The account describes an analyser installed in April 2019 using **cavity ring-down spectroscopy**: carbon dioxide is quantified through its effect on how quickly light decays inside an optical cavity. Reference gases of known composition calibrate the measurements.

Local influences still matter. The documented selection procedure identifies periods affected by variability and upslope air influenced by vegetation. Selection flags distinguish background observations; the underlying hourly data are retained. This is a description of a professional monitoring system, not a home sampling procedure.

The useful question is consequently not whether the location has any local influences. It is how the programme identifies those influences, checks instruments and documents which observations enter its background record.

## Why does the line rise and fall each year?

The seasonal pattern reflects changing exchange with land vegetation, especially in the Northern Hemisphere. Photosynthesis removes carbon dioxide from air during the growing season; respiration and decomposition return carbon. The larger extent of northern land and vegetation helps explain the strong northern seasonal signal. [NOAA's seasonal explanation](https://gml.noaa.gov/infodata/behind_the_scenes/gases.html)

A seasonal decrease is therefore not evidence that the long-term human contribution has disappeared. Likewise, a seasonal increase should not be described as a direct measurement of that month's industrial emissions.

The NOAA graph distinguishes monthly means from values adjusted for seasonality. Neither is a forecast; check the legend before comparing.

## How can you compare two published values correctly?

On the NOAA Mauna Loa page checked on **8 September 2026**, the displayed update date was **5 August 2026**. It listed **July 2026: 429.12 ppm** and **July 2025: 427.87 ppm**.

The difference is:

**429.12 − 427.87 = 1.25 ppm.**

That compares two displayed monthly means for the same calendar month. It is not today's reading, the difference between annual means, or a conversion into annual emissions. NOAA notes that its latest year remains preliminary.

Use this original comparison record before doing arithmetic:

| Check | Record for this example | Why retain it? |
| --- | --- | --- |
| Provider and series | NOAA Mauna Loa monthly means | Prevents switching programmes unnoticed |
| Periods | July 2026 and July 2025 | Keeps months distinct from annual averages |
| Unit | ppm | Prevents treating abundance as temperature |
| Release context | Page dated 5 August 2026; checked 8 September | Shows which displayed values were used |
| Calculation | Later value minus earlier value | Makes the 1.25 ppm difference reproducible |

This subtraction is not a named annual-growth-rate statistic.

## Is Mauna Loa the global average?

No. NOAA's global monthly series averages observations from a network of marine surface sites. Its construction differs from the single high-elevation Mauna Loa record. Shared units do not make the geographic sampling identical.

Keep location and averaging method attached to a number. If one chart shows Mauna Loa and another a global marine-surface average, a difference between them does not automatically indicate an error.

The same principle applies through time. A chart extending before 1958 cannot consist entirely of direct Mauna Loa measurements. Identify the additional record and method in its documentation rather than assuming the instrument observed every year shown.

## Does the upward curve alone establish the cause?

The curve establishes an increase in the measured abundance. Identifying its cause requires additional evidence.

Scripps' [explanation of human causation](https://keelingcurve.ucsd.edu/2018/09/19/is-the-current-rise-in-co2-definitely-caused-by-human-activities/) connects fossil-fuel emissions with carbon accumulating in the atmosphere, oceans and land. The accounting includes carbon taken up outside the atmosphere; emitted carbon does not all remain airborne.

Chemical evidence adds another test. **Isotopes** are forms of an element with different numbers of neutrons. Scripps' [flask-measurement explanation](https://keelingcurve.ucsd.edu/2013/05/20/why-scientists-still-collect-co2-in-flasks/) describes carbon-isotope analysis, including the absence of carbon-14 in fossil-fuel carbon after its radioactive decay over geological time. Such measurements provide source information that a concentration line alone cannot.

This strengthens, rather than weakens, the explanation: human causation is supported by converging evidence, not simply asserted from a rising line.

## How does an observed curve connect to future projections?

Observations and projections answer different questions. The curve records measured atmospheric change; a projection examines outcomes under specified future conditions. Our [climate-models guide](/climate-future-what-models-project/) explains that distinction, and the [SSP scenario guide](/climate-scenarios-ssp-pathways-explained/) decodes the conditional labels.

Extending the curve with a ruler is not a climate assessment. The practical reading sequence is simpler: identify the series, read its units and processing, compare matching periods, and keep the causal evidence separate from the arithmetic.

## Sources

Primary pages linked above were opened and read on 8 September 2026: NOAA Global Monitoring Laboratory's Mauna Loa trends, global trends, measurement-method and seasonal explanations; Scripps Institution of Oceanography's history, human-causation and flask-analysis articles. Historical methods and dated observations are identified as such. No monitoring instrument or climate model was operated for this guide.

## Frequently asked questions

**What does 400 ppm of carbon dioxide mean?**

It means 400 carbon dioxide molecules per million dry-air molecules, equivalent to 0.04%. The denominator excludes water vapour. Here 400 ppm is an illustrative unit conversion, not a current atmospheric reading. A ppm value describes abundance; it is neither a temperature nor an annual emissions total.

**Why does the Keeling Curve fall seasonally?**

Seasonal exchange with land vegetation changes atmospheric carbon dioxide, particularly in the Northern Hemisphere. Photosynthesis removes carbon during the growing season, while respiration and decomposition return it. A seasonal dip does not demonstrate that the long-term increase has ended or that human emissions have fallen to zero.

**Is the Mauna Loa reading the global average?**

No. NOAA's Mauna Loa series represents a particular high-elevation monitoring location, while its global monthly series combines observations from marine surface sites. Keep the provider, location, averaging period and processing attached to any number. Matching units alone do not make two differently sampled records interchangeable.

**Do researchers use every observation in the background curve?**

No. NOAA's documented method distinguishes background observations from periods affected by local influences and variability. It uses selection flags while retaining underlying hourly data, alongside instrument calibration. This is a professional measurement procedure; a graph reader should consult the relevant data notes rather than assuming all readings enter the background average.

**How do scientists identify the human contribution?**

The rising concentration record is considered alongside carbon accounting and chemical evidence. Fossil-fuel emissions add carbon distributed among the atmosphere, ocean and land; isotope measurements help identify sources. The absence of carbon-14 in fossil-fuel carbon supplies information beyond the curve's shape. No single plotted line carries the entire attribution argument.


---

# Weather vs. Climate: The Difference That Matters

> Weather is the short-term state of the atmosphere at a particular time and place, including rain, wind, and temperature. Climate is the longer-term pattern and distribution of weather across decades, including averages, variability, seasons, and extremes. A single cold day or heat wave is weather; changes in how often or intensely such events occur can be evidence of climate change.

Source: https://climateofourfuture.org/weather-vs-climate/  
Publisher: Climate in Plain Sight  
Published: 2026-07-19  
Updated: 2026-08-25

## Weather is the event; climate is the pattern

Weather describes short-term atmospheric conditions at a particular place and time: today's temperature, tomorrow's rain, this afternoon's wind. Climate describes the longer-term distribution and patterns of weather for a region, season, or the planet. One snowy day is weather; a decades-long shift in the frequency, intensity, timing, or average of such days is climate.

The distinction does not mean weather and climate are unrelated. Climate shapes the range and odds from which weather emerges, while individual weather events are the observations that accumulate into a climate record. Think of climate as the loaded deck and weather as the next hand—not because the outcome is fixed, but because the probabilities matter.

## Weather vs. climate at a glance

| Question | Weather | Climate |
|---|---|---|
| Timescale | Minutes to days or weeks | Decades and longer patterns |
| Geographic scale | Usually local or regional | Local, regional, continental, or global |
| Example | A thunderstorm crosses town tonight | Heavy downpours become more common over decades |
| Typical question | “Will it rain tomorrow?” | “How has winter rainfall changed?” |
| Main tools | Forecast models, radar, satellites, observations | Long records, statistics, climate models, paleoclimate evidence |
| Predictability | Specific conditions for coming hours or days | Long-term averages, ranges, risks, and trends |

NASA's [weather-and-climate explanation](https://science.nasa.gov/climate-change/faq/whats-the-difference-between-weather-and-climate/) describes weather on timescales from minutes and hours to days and weeks, while climate concerns longer-term averages over several decades. “Average” is only part of the story, however. Climate also includes variability, seasonality, extremes, and the likelihood of crossing important thresholds.

## Climate is more than average temperature

Suppose two cities both average 70°F over a month. One could remain close to 70°F every day; the other could swing between 45°F and 95°F. Their means match, but their climates do not feel—or function—the same way.

A useful climate description may include:

- Average temperature and precipitation
- Typical seasonal timing
- Day-to-day and year-to-year variability
- The frequency and intensity of extremes
- Humidity, wind, snow cover, and soil moisture
- Connections to oceans, ice, land surface, and ecosystems

That is why climate change can show up as changes in heat extremes, heavy rainfall, drought risk, snowpack, growing seasons, or coastal flooding even when a reader is looking only for a change in one local annual average.

The World Meteorological Organization commonly uses 30-year periods to calculate standard climate normals. A 30-year window is not a magic boundary at which weather puts on a tweed jacket and becomes climate. It is long enough to describe typical conditions while smoothing much short-term noise.

## How can weather be unpredictable while climate is predictable?

Specific weather depends on the atmosphere's exact evolving state. Small differences in initial conditions can grow, limiting detailed forecasts as lead time increases. Climate projections ask a different kind of question: how do the statistics of weather respond when greenhouse gases, solar energy, volcanic particles, land cover, or other influences change?

You cannot reliably predict the result of one coin toss, but you can estimate the distribution of results across many tosses if you know the coin. Similarly, a climate model does not need to identify the temperature on a particular street decades from now to project that heat extremes become more likely as the average climate warms.

This analogy also has limits. Weather is not a set of independent coin tosses, and Earth's climate system contains interacting feedbacks. Scientists test models against physical laws, observations, and past climate changes rather than relying on the metaphor.

## Does a cold day disprove global warming?

No. Global warming is a long-term increase in global average temperature caused chiefly today by human greenhouse-gas emissions. Cold weather still occurs because seasons, geography, circulation, and natural variability continue operating in a warmer climate.

A new personal record low in one town says little about the global trend by itself. Likewise, one scorching afternoon does not independently prove long-term climate change. Evidence comes from many records over broad areas and long periods: surface and ocean temperatures, glacier and ice-sheet loss, sea level, atmospheric measurements, satellite observations, seasonal changes, and more.

The useful question is not “Did cold vanish?” It is “How have the distribution and odds changed?” A small shift in the center of a temperature distribution can produce a substantial change at its hottest tail, while cold extremes become less common overall without becoming impossible.

## Does one heat wave prove climate change?

Also no—not by itself. Heat waves occurred before modern human-caused warming. But a warmer baseline can make many heat extremes more likely and more intense. Event-attribution studies compare the probability or intensity of a particular event in the observed climate with modeled conditions in a world without the human influence.

Confidence is especially strong for increases in hot extremes. Other hazards are more complicated because local rainfall, soils, circulation, land management, ignition, coastal development, and many other factors contribute. The detailed guide to [climate change and extreme weather](/climate-change-extreme-weather/) separates those levels of confidence.

Treating every event as either “caused by climate change” or “completely natural” is usually the wrong frame. Climate change often modifies the background odds or severity while immediate weather mechanisms still produce the event.

## Global trend, local experience

Global average warming does not mean every place warms at the same rate or every season changes identically. Land generally warms faster than ocean; the Arctic has warmed especially rapidly; circulation and local geography shape regional outcomes. Natural variability can temporarily reinforce or offset the long-term trend in a particular region.

This is why a local graph needs context. A short record may begin during an unusually warm or cool period. A single station can be affected by site moves, instrument changes, development, or missing data. Climate scientists adjust and compare records using documented methods, nearby stations, ocean observations, satellites, and independent datasets.

Those corrections are not evidence of a cooked ledger. Raw measurements often require calibration in every serious field. The relevant questions are whether methods are transparent, physically justified, tested, and independently reproduced.

## Forecasts and projections are not the same product

A **weather forecast** estimates the atmospheric state over coming hours or days, usually from current conditions. A **climate projection** describes possible future averages, variability, and risks under specified assumptions, such as a greenhouse-gas emissions pathway.

Projections are conditional: if emissions follow one path, models show one range of outcomes; if they follow another, the range changes. That is not a weakness equivalent to shrugging. It reflects the fact that future human choices are inputs, not forces of nature known in advance.

Near-term planning may use both. A city deciding whether to open cooling centers needs a weather forecast for this week's heat. A city deciding the design conditions for housing and electricity infrastructure needs climate information about how heat risk is changing across decades.

## Where the greenhouse effect fits

Weather moves energy and moisture through the atmosphere every day. The [enhanced greenhouse effect](/greenhouse-effect-explained/) changes the larger energy balance within which that movement occurs. Rising greenhouse-gas concentrations do not dictate each weather map; they add warming to the climate system, and that shift influences long-term distributions.

Natural drivers still matter. El Niño and La Niña redistribute heat and change weather patterns from year to year. Volcanic eruptions can temporarily cool global climate by reflecting sunlight. Solar variations and internal ocean-atmosphere cycles also contribute variability. The scientific conclusion that humans drive the modern long-term warming trend includes, rather than ignores, those influences.

## Five common mix-ups

### “The forecast was wrong, so climate models are unreliable”

Forecasts and projections answer different questions and begin from different sources of uncertainty. Difficulty predicting one exact storm weeks ahead does not erase the ability to calculate how added greenhouse gases change Earth's energy balance or long-term heat statistics.

### “Climate always changes naturally”

Correct but incomplete. Climate has changed for natural reasons. That does not identify the cause of current change. Evidence shows that human greenhouse-gas emissions are the principal driver of modern global warming.

### “Global warming means every year must be hotter than the last”

No. Natural variability creates ups and downs around a rising long-term trend. A staircase can go upward without every patch of carpet being higher than the centimeter before it.

### “A local trend represents the entire planet”

Local records are important, but global climate is assembled from broad land, ocean, atmosphere, and ice observations. One region can temporarily cool while the planet as a whole warms.

### “Adaptation means better forecasting”

Forecasts support adaptation, but adaptation is wider: heat plans, flood-resilient infrastructure, water management, ecosystem protection, and many other changes that reduce harm. Mitigation reduces emissions. The two-response framework is explained in [climate mitigation versus adaptation](/climate-mitigation-vs-adaptation/).

## How to read a climate claim well

When you encounter a striking headline, ask:

1. Is the claim about one event, a trend, or a projection?
2. What period and geographic area does it cover?
3. Is it reporting an average, an extreme, or a probability?
4. Does the source distinguish observation from model projection?
5. Are uncertainty and alternative influences described?

A good claim makes its scale visible. “Rain increased” is underspecified. “Annual heavy-precipitation events increased in this defined region over this measured period” is testable—even if it needs a footnote that could double as light furniture.

The weather-climate distinction is not a loophole for dismissing lived experience. It is the tool that places experience in a meaningful pattern. Weather tells you what coat to wear today. Climate helps decide what kind of coat rack a region will need.

## Frequently asked questions

**What is the main difference between weather and climate?**

The main difference is timescale and the kind of question being asked. Weather describes specific atmospheric conditions over minutes, days, or weeks. Climate describes longer-term patterns across decades, including averages, seasonal cycles, variability, and extremes. Weather is today's outcome; climate helps describe the range and odds of possible outcomes.

**Does a cold winter disprove global warming?**

No. Cold days and winters remain possible in a warming climate because seasons, circulation, geography, and natural variability continue. Global warming is identified from broad, long-term evidence across the atmosphere, ocean, land, and ice. The relevant question is how the frequency and intensity of cold and hot conditions change over time.

**Can one heat wave be blamed on climate change?**

A single event usually has multiple causes. Attribution research asks whether human-caused climate change changed an event's probability or intensity, not whether it supplied the only cause. Evidence is especially strong that warming has increased many heat extremes, while confidence and mechanisms differ for droughts, storms, floods, and other hazards by region.

**Why can scientists project climate decades ahead but not forecast weather that far?**

Detailed weather forecasts depend on the atmosphere's exact initial state, and small errors grow over time. Climate projections ask how long-term statistics respond to influences such as greenhouse-gas concentrations. They can project ranges and changing risks without predicting the exact weather in one town on one distant date.

**Is climate just average weather?**

Average weather is part of climate, but not the whole definition. Climate also includes variability, seasonal timing, the frequency and severity of extremes, and patterns in precipitation, wind, humidity, snow, and other conditions. Two places can share the same average temperature yet have very different ranges and risks.

**How long does it take to measure climate?**

Climate is evaluated with long records, commonly using 30-year periods for standard climate normals. Scientists can also study longer change using instruments, satellites, ocean records, ice cores, tree rings, sediments, and other evidence. A 30-year period is a convention for stable comparison, not a claim that shorter observations contain no useful information.


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