Are humans responsible for climate change?

Yes, humans are the primary cause of the observed climate change (global warming) since the Industrial Revolution, particularly the rapid warming since the mid-20th century. This is the overwhelming scientific consensus, described as “unequivocal” by the Intergovernmental Panel on Climate Change (IPCC).[1]

Scientific Consensus

•Multiple independent analyses of the peer-reviewed literature find that more than 99% of climate science papers agree that human activities are the main driver of recent climate change. A 2021 study of over 88,000 papers (examining a large random subset plus targeted searches) found only a tiny handful of skeptical papers, concluding the consensus exceeds 99%. Earlier work (e.g., covering 1991–2012) found ~97%.[2]

•Surveys of actively publishing climate scientists similarly show 97–100% agreement that humans are causing most of the warming.[3]

•Leading scientific organizations worldwide—including NASA, NOAA, the National Academies of Sciences, the American Association for the Advancement of Science, and others—endorse this position. NASA states that multiple studies show warming trends over the past century are extremely likely due to human activities.[4]

The IPCC’s Sixth Assessment Report (AR6, 2021) states: “It is unequivocal that human influence has warmed the atmosphere, ocean and land.” Human influence is the principal driver of many observed changes across the climate system. Best estimates attribute essentially all of the ~1.1°C (about 2°F) of global surface warming since 1850–1900 to human activities.[5]

Key Evidence

Multiple independent lines of evidence converge on this conclusion:

1.Greenhouse gas increases from human activities: Atmospheric CO₂, methane, and nitrous oxide have risen sharply due to burning fossil fuels (coal, oil, gas), deforestation, and other land-use changes. CO₂ levels are higher than at any time in at least the last 800,000 years (from ice cores), and the increase carries a clear isotopic “fingerprint” matching fossil carbon (depleted in carbon-14 and with specific carbon-13 ratios). The greenhouse effect of these gases is well-established physics.[5]

2.Climate models and attribution studies: Models that include only natural factors (solar variability, volcanoes, internal variability like El Niño) cannot reproduce the observed warming. Models that include human greenhouse gas emissions and aerosols match the observations closely. Observed warming is only reproduced when human influence is included.[1]

3.Pattern of warming (“fingerprint”): The troposphere (lower atmosphere) is warming while the stratosphere is cooling—exactly what greenhouse gas forcing predicts, and inconsistent with increased solar output (which would warm both). Nights are warming faster than days in many places, and winters faster than summers in some regions, consistent with greenhouse forcing.[5]

4.Rate and paleoclimate context: The recent rate of warming is unprecedented in at least the last 2,000 years (and far faster than typical post-ice-age recoveries). Natural cycles (Milankovitch orbital changes, etc.) operate on much longer timescales and cannot explain the rapid modern rise.[6]

5.Other observations: Ocean heat content is rising (oceans absorb most excess heat), sea levels are rising, ice sheets and glaciers are losing mass, Arctic sea ice is declining, and extreme heat events are increasing in ways attributable to human influence.[7]

Natural factors still play roles in year-to-year and regional variability, and aerosols from pollution have a partial cooling effect that has masked some warming. However, they do not explain the long-term global trend. Claims that the Sun, orbital changes, or pure natural variability are the main cause are inconsistent with the data.[5]

In short, the evidence from direct measurements, paleoclimate records, basic physics, and sophisticated modeling all point to the same conclusion: human emissions of greenhouse gases are driving the current climate change. This understanding has strengthened over successive IPCC reports, moving from “discernible” influence in the 1990s to “unequivocal” today.

Citations (7)

1ipcc.chGovernment
https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_WGI_FAQ_Chapter_03.pdf
Backs: “This is the overwhelming scientific consensus, described as “unequivocal” by the Intergovernmental Panel on Climate Change (IPCC).”
2cornell.eduAcademic
https://news.cornell.edu/stories/2021/10/more-999-studies-agree-humans-caused-climate-change
Backs: “A 2021 study of over 88,000 papers (examining a large random subset plus targeted searches) found only a tiny handful of skeptical papers, concluding the consensus exceeds 99%. Earlier work (e.g., covering 1991–2012) found ~97%.”
3skepticalscience.comNonprofits and think tanks
https://skepticalscience.com/print.php?r=18
Backs: “Surveys of actively publishing climate scientists similarly show 97–100% agreement that humans are causing most of the warming.”
4nasa.govGovernment
https://science.nasa.gov/climate-change/scientific-consensus/?mod=article_inline
Backs: “NASA states that multiple studies show warming trends over the past century are extremely likely due to human activities.”
5nasa.govGovernment
https://science.nasa.gov/climate-change/causes/
Backs: “Best estimates attribute essentially all of the ~1.1°C (about 2°F) of global surface warming since 1850–1900 to human activities.”
6archive.isData and tools
https://archive.is/2025.11.13-121149/https://science.nasa.gov/climate-change/evidence/
Backs: “Natural cycles (Milankovitch orbital changes, etc.) operate on much longer timescales and cannot explain the rapid modern rise.”
7climate.govGovernment
https://www.climate.gov/news-features/climate-qa/what-evidence-exists-earth-warming-and-humans-are-main-cause
Backs: “Ocean heat content is rising (oceans absorb most excess heat), sea levels are rising, ice sheets and glaciers are losing mass, Arctic sea ice is declining, and extreme heat events are increasing in ways attributable to human influence.”