Are humans responsible for climate change?

Yes, humans are the primary cause of recent climate change (global warming since the Industrial Revolution). This is the overwhelming conclusion of climate science, based on multiple independent lines of evidence, and it is described as “unequivocal” by the Intergovernmental Panel on Climate Change (IPCC).[1]

Scientific Consensus

•More than 99% of peer-reviewed scientific papers on climate change agree that it is mainly caused by human activities. A 2021 survey of over 88,000 studies found only a tiny handful of dissenting papers. Earlier analyses (e.g., ~97% consensus) have been updated and strengthened.[2]

•Virtually all actively publishing climate scientists and major scientific organizations worldwide (NASA, NOAA, Royal Society, national academies, etc.) endorse this position. Surveys of experts show 97–100% agreement, higher among those with the greatest expertise.[3]

•The IPCC’s Sixth Assessment Report (AR6, 2021) states: “It is unequivocal that human influence has warmed the atmosphere, ocean and land.” Human activities, principally greenhouse gas emissions, have caused global surface temperature to rise about 1.1°C above 1850–1900 levels (as of ~2011–2020 data; it has continued since).[4]

Key Evidence

Multiple converging lines of evidence establish human responsibility:

1.Greenhouse gas increases from human activities: Atmospheric CO₂ has risen from ~280 ppm pre-industrially to over 420 ppm today, primarily from burning fossil fuels (coal, oil, gas), with additional contributions from deforestation, agriculture (methane, nitrous oxide), and industry. Isotopic analysis (e.g., carbon-12 vs. carbon-13 ratios) confirms the excess CO₂ comes from fossil sources, not natural ones like volcanoes (which contribute ~1% of current human emissions). Methane and other gases have also risen sharply.[5]

2.Basic physics: Greenhouse gases trap heat (infrared radiation). This has been understood since the 19th century. More GHGs strengthen the greenhouse effect, warming the surface and lower atmosphere.

3.Climate models and attribution studies (“fingerprinting”): Models that include only natural factors (solar variability, volcanoes, orbital changes) cannot reproduce the observed warming of ~1.1°C. Models including human forcings (mainly GHGs, partially offset by aerosols) match observations closely. The likely range of human-caused warming from 1850–1900 to 2010–2019 is 0.8–1.3°C (best estimate ~1.07°C), while natural drivers contribute roughly –0.1 to +0.1°C.[1]

•Specific fingerprints include: warming of the troposphere + cooling of the stratosphere (expected from GHGs, opposite of what increased solar output would cause); greater warming at night and in winter in some patterns; ocean heat content increase; and more.

4.Rate and pattern of change: The current warming rate is unprecedented in at least the last 2,000 years (and far faster than post-ice age recoveries). Paleoclimate records (ice cores, tree rings, sediments) show past natural changes occurred much more slowly. Observed changes (rising temperatures, melting ice, sea level rise, ocean acidification, shifts in extremes) align with human-driven forcing.[6]

5.Ruling out alternatives: Solar output has not increased in a way that explains the warming (and the stratospheric cooling contradicts it). Volcanic activity causes temporary cooling. Internal variability (e.g., El Niño) causes short-term fluctuations but not the long-term trend.

Natural climate variations have always existed (ice ages, etc.), and they continue to play a role in year-to-year or regional weather. However, they cannot explain the rapid, global-scale warming of the past ~150 years—especially the acceleration since the mid-20th century. Human influence dominates.[7]

Context and Nuance

•Not all climate change is human-caused historically: Earth’s climate has varied naturally over geologic time due to orbital cycles, solar changes, plate tectonics, etc. The current episode is distinct in speed and cause.

•Aerosols and other factors: Human-emitted aerosols have a net cooling effect that partially masks GHG warming. Land-use changes also play a role.

•Impacts: Human-caused warming is already driving more frequent/intense heat extremes, heavier precipitation in many areas, sea level rise, cryosphere loss, and ecosystem shifts. Future warming depends on emissions pathways.

•Claims denying or minimizing human responsibility are not supported by the evidence or the peer-reviewed literature; they often rely on outdated data, misrepresentations, or non-expert sources.

In short, the science is settled at a very high confidence level: humans are responsible for essentially all of the observed global warming since the late 19th century through greenhouse gas emissions and related activities. This is one of the most robust findings in modern science. For primary sources, see IPCC AR6 Working Group I reports, NASA/NOAA climate pages, and the peer-reviewed literature they synthesize.

Citations (7)

1ipcc.chGovernment
https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/
Backs: “This is the overwhelming conclusion of climate science, based on multiple independent lines of evidence, and it is 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: “Earlier analyses (e.g., ~97% consensus) have been updated and strengthened.”
3nasa.govGovernment
https://science.nasa.gov/climate-change/scientific-consensus/
Backs: “Surveys of experts show 97–100% agreement, higher among those with the greatest expertise.”
4ipcc.chGovernment
https://report.ipcc.ch/ar6syr/headline.html
Backs: ““It is unequivocal that human influence has warmed the atmosphere, ocean and land.” Human activities, principally greenhouse gas emissions, have caused global surface temperature to rise about 1.1°C above 1850–1900 levels (as of ~2011–2020 data; it has continued since).”
5royalsociety.orgAcademic
https://royalsociety.org/news-resources/projects/climate-change-evidence-causes/basics-of-climate-change/
Backs: “Isotopic analysis (e.g., carbon-12 vs. carbon-13 ratios) confirms the excess CO₂ comes from fossil sources, not natural ones like volcanoes (which contribute ~1% of current human emissions). Methane and other gases have also risen sharply.”
6ipcc.chGovernment
https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_WGI_FAQ_Chapter_03.pdf
Backs: “Observed changes (rising temperatures, melting ice, sea level rise, ocean acidification, shifts in extremes) align with human-driven forcing.”
7royalsociety.orgAcademic
https://royalsociety.org/news-resources/projects/climate-change-evidence-causes/
Backs: “However, they cannot explain the rapid, global-scale warming of the past ~150 years—especially the acceleration since the mid-20th century. Human influence dominates.”