Are humans responsible for climate change?

Yes, humans are the primary cause of recent 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 show extremely high agreement: a 2013 study found ~97% consensus among papers taking a position, and a 2021 survey of over 88,000 climate-related papers (2012–2020) found greater than 99.9% agreement that climate change is mainly human-caused (only a handful of skeptical papers in large samples).[2]

•Surveys of climate scientists and experts consistently show 97–100% agreement, with higher expertise correlating to stronger consensus. Leading scientific organizations worldwide (NASA, NOAA, AAAS, national academies, etc.) endorse this position.[3]

•The IPCC’s Sixth Assessment Report (AR6, 2021) states: “It is unequivocal that human influence has warmed the atmosphere, ocean and land.” The best estimate of human-induced warming from 1850–1900 to 2010–2019 is about 1.07°C (likely range 0.8–1.3°C), matching the observed warming, while natural forcings contributed roughly –0.1 to +0.1°C.[1]

Key Evidence

Multiple independent lines of evidence converge on this conclusion:

1.Greenhouse gas increases from human activities: Atmospheric CO₂ has risen ~50% since pre-industrial times (from ~280 ppm to over 410–420 ppm), with methane and nitrous oxide also up significantly. Levels and rates of increase are unprecedented in at least 800,000 years (from ice cores). Isotopic analysis (“fingerprint”) shows the extra CO₂ comes from burning fossil fuels (coal, oil, gas), not natural sources. Human emissions (fossil fuels, deforestation, agriculture, industry) are the dominant source.[4]

2.Basic physics and the greenhouse effect: CO₂ and other GHGs trap heat. This has been understood since the 19th century. More GHGs → more warming, all else equal.

3.Climate models and attribution studies: Models that include only natural factors (solar variability, volcanoes, internal variability) cannot reproduce the observed warming. Models including human influences (GHGs + aerosols) match observations closely across temperature, ocean heat content, etc. “Fingerprinting” shows the pattern of warming (troposphere warming + stratosphere cooling, greater land/nighttime/Arctic warming, etc.) matches greenhouse forcing, not solar or other natural drivers.[5]

4.Observations of change: Global surface temperature has risen ~1.1–1.2°C since the late 19th century (most since the 1970s); oceans have absorbed vast heat and CO₂ (causing acidification); ice sheets/glaciers/sea ice are shrinking; sea level is rising; extremes (heatwaves, etc.) are increasing in ways attributable to human influence. The recent rate of warming exceeds natural variations over the past 2,000+ years.[6]

5.Natural factors are insufficient: Solar output has been stable or slightly declining in recent decades; volcanic effects are short-lived and mostly cooling. These cannot explain the long-term trend or observed patterns.

Climate has always changed naturally over Earth’s history (orbital cycles, solar changes, volcanoes, etc.), but the current rapid warming is distinct in speed, cause (human GHG emissions), and coincidence with the industrial era. Human activities are the dominant driver of the changes observed in recent decades.[7]

This conclusion is based on decades of data from observations, paleoclimate records, physics, and models, assessed by thousands of scientists. While uncertainties remain in exact projections, regional details, or feedbacks, the core attribution of recent warming to humans is settled science at the highest confidence levels.

Citations (7)

1ipcc.chGovernment
https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/
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: “Multiple independent analyses of the peer-reviewed literature show extremely high agreement: a 2013 study found ~97% consensus among papers taking a position, and a 2021 survey of over 88,000 climate-related papers (2012–2020) found greater than 99.9% agreement that climate change is mainly human-caused (only a…”
3climate.govGovernment
https://www.climate.gov/news-features/climate-qa/isnt-there-lot-disagreement-among-climate-scientists-about-global-warming
Backs: “Leading scientific organizations worldwide (NASA, NOAA, AAAS, national academies, etc.) endorse this position.”
4nasa.govGovernment
https://science.nasa.gov/climate-change/causes/
Backs: “Human emissions (fossil fuels, deforestation, agriculture, industry) are the dominant source.”
5ipcc.chGovernment
https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_WGI_FAQ_Chapter_03.pdf
Backs: ““Fingerprinting” shows the pattern of warming (troposphere warming + stratosphere cooling, greater land/nighttime/Arctic warming, etc.) matches greenhouse forcing, not solar or other natural drivers.”
6nasa.govGovernment
https://science.nasa.gov/climate-change/evidence
Backs: “The recent rate of warming exceeds natural variations over the past 2,000+ years.”
7archive.mdData and tools
https://archive.md/2024.11.07-200429/https://www.climate.gov/news-features/climate-qa/what-evidence-exists-earth-warming-and-humans-are-main-cause
Backs: “Human activities are the dominant driver of the changes observed in recent decades.”