Are humans responsible for climate change?

Yes, humans are the primary cause of recent climate change (global warming since the Industrial Revolution, especially the rapid warming of the past 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 near-unanimous agreement. A 2013 study found ~97% consensus; a 2021 survey of over 88,000 climate-related papers (2012–2020) found greater than 99% (or >99.9% in some framings) agree that humans are the main cause. Skeptical papers are extremely rare.[2]

•Surveys of climate scientists show 97–100% agreement, with higher expertise correlating to stronger consensus. Leading organizations (NASA, NOAA, AAAS, National Academies, and others worldwide) 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 is that humans caused about 1.07°C of the ~1.1°C warming from 1850–1900 to 2010–2019 (likely range 0.8–1.3°C). Greenhouse gases (mainly CO₂ from fossil fuels) contributed 1.0–2.0°C of warming, partially offset by aerosols; natural drivers (solar, volcanic) contributed roughly –0.1 to +0.1°C.[4]

Key Evidence

Multiple independent lines of evidence converge:

1.Greenhouse gas increases are human-caused: Atmospheric CO₂, methane, and nitrous oxide have risen sharply since the Industrial Revolution due to burning fossil fuels, deforestation, and industrial/agricultural activities. Concentrations are unprecedented in at least 800,000 years. Isotopic “fingerprints” confirm the CO₂ comes from fossil fuels, not natural sources.[5]

2.Physics of the greenhouse effect: These gases trap heat. The basic science has been understood since the 19th century.

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 (especially GHGs) match observations closely, including warming of the lower atmosphere/surface, cooling of the stratosphere, ocean heat content rise, and other patterns.[6]

4.Rate and pattern of change: The current rate of warming is faster than natural changes in recent millennia (e.g., faster than post-ice-age warming). Paleoclimate records (ice cores, tree rings, sediments) show no natural analog for the recent multi-decade rate. Observed changes extend to oceans, cryosphere (ice melt), biosphere, and extremes.[7]

5.Ruling out alternatives: Solar output has been stable or slightly declining in recent decades; volcanic activity and other natural forcings do not match the magnitude, timing, or vertical/spatial patterns of warming.

Natural climate variability (e.g., El Niño, orbital cycles) and past climate shifts exist, but they do not explain the post-industrial warming. Human influence is now detectable in many climate system components and is the dominant driver of observed changes since the mid-20th century.[8]

In short, the evidence from observations, physics, paleoclimate data, and models is robust and has strengthened over successive IPCC assessments (from “discernible” in 1995 to “unequivocal” today). While climate has always changed naturally, the current rapid warming is primarily anthropogenic.

Citations (8)

1climate.govGovernment
https://www.climate.gov/news-features/climate-qa/isnt-there-lot-disagreement-among-climate-scientists-about-global-warming
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 2013 study found ~97% consensus; a 2021 survey of over 88,000 climate-related papers (2012–2020) found greater than 99% (or >99.9% in some framings) agree that humans are the main cause. Skeptical papers are extremely rare.”
3nasa.govGovernment
https://science.nasa.gov/climate-change/scientific-consensus/
Backs: “Leading organizations (NASA, NOAA, AAAS, National Academies, and others worldwide) endorse this position.”
4ipcc.chGovernment
https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-1/
Backs: “Greenhouse gases (mainly CO₂ from fossil fuels) contributed 1.0–2.0°C of warming, partially offset by aerosols; natural drivers (solar, volcanic) contributed roughly –0.1 to +0.1°C.”
5nasa.govGovernment
https://science.nasa.gov/climate-change/causes/
Backs: “Isotopic “fingerprints” confirm the CO₂ comes from fossil fuels, not natural sources.”
6ipcc.chGovernment
https://www.ipcc.ch/report/ar6/wg1/downloads/faqs/IPCC_AR6_WGI_FAQ_Chapter_03.pdf
Backs: “Models including human influences (especially GHGs) match observations closely, including warming of the lower atmosphere/surface, cooling of the stratosphere, ocean heat content rise, and other patterns.”
7archive.phData and tools
https://archive.ph/2024.10.06-154745/https://science.nasa.gov/climate-change/evidence/
Backs: “Observed changes extend to oceans, cryosphere (ice melt), biosphere, and extremes.”
8ipcc.chGovernment
https://www.ipcc.ch/report/ar6/syr/longer-report
Backs: “Human influence is now detectable in many climate system components and is the dominant driver of observed changes since the mid-20th century.”