This overview gathers the evidence side of the Education Center: what is measured, why scientists connect recent warming primarily to human activity, how weather and climate interact, and what projections can and cannot tell us.
Data Snapshot
Major climate indicators at a glance.
These figures summarize several independent lines of evidence: temperature records, greenhouse gases, ocean heat, sea level, ice, and emissions. They are not meant to replace the source reports; they are a quick data layer before the deeper explanations beloh.
Sources: WMO, NOAA Climate.gov, IPCC AR6, NSIDC, Berkeley Earth, and Global Carbon Project.
Temperature
Warming compared with the 1850-1900 baseline.
Different datasets use different methods, but they show the same basic direction: the planet has warmed sharply since the late nineteenth century.
2011-2020: IPCC AR6. 2025: WMO State of the Global Climate 2025. 2024: Berkeley Earth global temperature analysis.
Atmosphere
Carbon dioxide has climbed far above pre-industrial levels.
CO2 varies seasonally, but the long-term rise is clear. NOAA describes today’s concentration as more than 50 percent above pre-industrial levels.
Source context: NOAA Climate.gov and NOAA Global Monitoring Laboratory carbon dioxide records.
Evidence Table
Observed indicators and what they show.
| Indicator | What is measured | What the evidence shows | Why it matters |
|---|---|---|---|
| Surface temperature | Global land and ocean temperature records | Recent years are the warmest in the instrumental record, with 2024 and 2025 near the top depending on dataset. | Shows the atmosphere and surface climate system warming across decades. |
| Atmospheric CO2 | Parts per million in the atmosphere | CO2 has risen from about 280 ppm before industrialization to above 420 ppm today. | Directly measures the main long-lived greenhouse gas added by fossil fuel use and land-use change. |
| Ocean heat | Heat stored in upper and deeper ocean layers | The ocean stores most excess heat, with recent years at record or near-record levels. | Confirms the planet is gaining energy, not merely experiencing surface-weather variability. |
| Sea level | Satellite and tide-gauge sea-level records | Global mean sea level has risen since satellite records began in 1993. | Raises coastal flood risk and affects long-term planning. |
| Ice and glaciers | Arctic sea ice, glaciers, snow, ice sheets | Arctic September sea ice has declined, and glaciers have continued losing mass. | Independent physical evidence of warming with water-supply and coastal implications. |
| Fossil CO2 emissions | Annual carbon dioxide emissions from fossil fuels and industry | Global Carbon Project estimated fossil CO2 emissions at about 37.4 billion tonnes in 2024. | Shows the human source driving continued greenhouse-gas accumulation. |
Cause and Confidence
Why scientists attribute recent warming mainly to human activity.
| Evidence type | Scientific meaning | Climate conclusion |
|---|---|---|
| Greenhouse-gas physics | CO2, methane, and nitrous oxide absorb outgoing infrared energy. | Adding these gases changes Earth’s energy balance. |
| Measured atmospheric chemistry | CO2 and other greenhouse gases have risen sharply since industrialization. | The cause is consistent with fossil fuels, industry, agriculture, and land-use change. |
| Pattern of warming | lower atmosphere and ocean warming, stratospheric cooling, ice loss, and sea-level rise align with greenhouse forcing. | The pattern is not well explained by solar variability alone. |
| Model comparisons | Models reproduce observed warming much better when human emissions are included. | Human influence is required to explain the modern warming pattern. |
| Independent indicators | Temperature, ocean heat, ice, sea level, and ecosystems show connected changes. | The conclusion is stronger because the evidence does not depend on one measurement system. |
Temperature dataGlobal temperature records show sustained warming
Global temperature has risen sharply since the late nineteenth century, and the warming is not limited to one agency, one instrument, or one country. WMO reports that 2015-2025 were the eleven warmest years on record. Its 2025 update estimates 2025 at about 1.43°C above the 1850-1900 average, making it the second or third warmest year recorded depending on the dataset.
Berkeley Earth reported 2024 as the warmest year in its instrumental record, about 1.62°C above the 1850-1900 baseline. Individual years still move up and down because of El Nino, volcanic aerosols, ocean variability, and weather patterns, but the multi-decade trend is the signal that matters.
Sources: WMO State of the Global Climate 2025, Berkeley Earth 2024 temperature report, and IPCC AR6 Synthesis Report.
CausesGreenhouse gases explain why the planet is gaining heat
The core cause is not mysterious: carbon dioxide, methane, nitrous oxide, and other greenhouse gases absorb outgoing infrared energy and change Earth’s energy balance. Human activity has increased those concentrations through fossil fuel combustion, cement production, agriculture, industry, and land-use change.
NOAA reports that atmospheric carbon dioxide is now more than 50 percent higher than pre-industrial levels. Global Carbon Project estimated fossil carbon dioxide emissions at a record high in 2024, around 37.4 billion tonnes of CO2. The physical fingerprint matters too: the lower atmosphere is warming while the upper stratosphere has cooled, a pattern expected from greenhouse-gas forcing rather than a brighter Sun.
Sources: NOAA Climate.gov carbon dioxide explainer, Global Carbon Project, and IPCC AR6.
Ocean and iceOceans, sea level, glaciers, and ice show the heat accumulating
The atmosphere is only one part of the evidence. The oceans absorb most of the excess heat trapped by greenhouse gases. WMO’s State of the Global Climate reports record or near-record ocean heat in recent years, with the ocean warming signal continuing across the upper and deeper layers.
Sea level is rising because ocean water expands as it warms and because land ice is melting. Glaciers have lost mass almost everywhere, and the global mean sea level measured by satellites has risen since 1993. Arctic sea ice has also declined substantially, especially in late-summer minimum extent.
Sources: WMO State of the Global Climate 2024, NOAA sea level information, and NSIDC Arctic Sea Ice news & Analysis.
Weather riskWeather extremes are changing, but attribution has to be specific
Climate change does not mean every storm, fire, flood, or drought has a single cause. It changes the background conditions in which events happen. A warmer atmosphere can hold more water vapor, increasing the potential for heavy rainfall. Higher baseline temperatures make heat extremes more likely and more intense in many regions.
Attribution science compares the probability or intensity of an event in today’s climate with a modeled world without the same human influence. Heat extremes are generally among the clearest categories. Heavy precipitation, drought, wildfire weather, tropical cyclones, and flooding often require more regional detail because land use, infrastructure, vegetation, water management, and exposure also shape damage.
Sources: IPCC AR6 Working Group I, IPCC AR6 Synthesis Report, and WMO extreme weather resources.
ProjectionsProjections show risk depends on future emissions
Climate projections are not guesses about next Tuesday’s weather. They are scenarios built from physics, observed data, land-use assumptions, energy pathways, aerosols, greenhouse gases, and human choices. They show that higher cumulative emissions generally mean more warming, higher sea level, larger heat risks, and greater pressure on ecosystems and communities.
The important point is that projections are conditional. They do not say one future is guaranteed. They say risk changes depending on emissions, adaptation, technology, land use, and policy. That makes climate projections useful for planning: they show why reducing emissions and preparing communities both matter.
Sources: IPCC AR6 Synthesis Report, IPCC AR6 Physical Science Basis, and WMO climate resources.
ConfidenceThe evidence is strong because independent indicators agree
The strongest case for climate change is not a single quote or graph. It is the agreement among independent evidence: thermometer records, ocean heat, satellite observations, glacier measurements, sea-level records, atmospheric chemistry, ecological changes, physical theory, and model experiments.
That does not mean every number is perfectly known or every local effect is settled. Scientific confidence varies by question. But the central conclusions are robust: the planet has warmed, greenhouse gases from human activity are the dominant cause of recent warming, impacts are already observable, and future risk depends heavily on emissions and preparedness.
Sources: IPCC AR6 Synthesis Report, WMO State of the Global Climate 2025, NOAA Climate.gov, and Berkeley Earth.
ACC takeaway
The evidence is broad, measurable, and practical.
Climate science is strongest when it is treated as a body of evidence rather than a slogan. The data above shows why ACC treats climate change as a real, measured risk while still encouraging clear wording, source-checking, and realistic comparisons.
References & further reading
Review the underlying data.
- WMO: State of the Global Climate 2025Current global climate indicators, temperature, ocean heat, sea level, and impacts.
- WMO: State of the Global Climate 2024Annual assessment of global climate indicators and observed change.
- IPCC AR6 Synthesis ReportIntegrated assessment of warming, causes, impacts, adaptation, and mitigation.
- IPCC AR6 Working Group IPhysical science basis for observed warming, attribution, and projections.
- NOAA Climate.gov: Atmospheric Carbon DioxideCarbon dioxide measurements and explanation of the greenhouse effect.
- Berkeley Earth: Global Temperature Report 2024Independent temperature dataset and annual global temperature analysis.
- Global Carbon ProjectAnnual carbon budget, fossil CO2 emissions, land-use emissions, and carbon sinks.
- NSIDC Arctic Sea Ice news & AnalysisArctic sea ice observations, trends, and seasonal updates.