Human-caused climate change
The IPCC Sixth Assessment Report (2021-2023) concludes it is unequivocal that human influence has warmed the atmosphere, ocean, and land. More than 97% of actively publishing climate scientists and over 99% of peer-reviewed climate papers endorse anthropogenic climate change.
What we know
Multiple independent lines of evidence support the conclusion that human activities, primarily the burning of fossil fuels and land-use change, are the dominant cause of observed global warming since the mid-20th century. These lines of evidence include direct atmospheric measurements of rising CO2 concentrations since continuous monitoring began at Mauna Loa in 1958, isotopic fingerprinting that links the increase specifically to fossil fuel combustion rather than natural sources, satellite measurements of declining outgoing long-wave radiation at wavelengths absorbed by greenhouse gases, and formal attribution studies that compare observed warming patterns against climate models run with and without human influence included.
The IPCC Sixth Assessment Report (AR6), published across 2021 to 2023, states plainly that "human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming." The AR6 Working Group I report finds it "extremely likely" that human influence caused more than half of the observed increase in global mean surface temperature between 1951 and 2010, and "virtually certain" that human-induced greenhouse gas forcing is the main driver of observed increases in heat extremes over land. Global average surface temperature has risen by approximately 1.1 to 1.2 degrees Celsius above pre-industrial levels as of the mid-2020s, with the rate of warming accelerating in recent decades rather than slowing.
Multiple independent surveys of the scientific literature and of climate scientists consistently find that 97 to 100 percent of actively publishing climate experts agree that recent global warming is primarily caused by human activity. A 2021 study examining 88,125 climate-related papers published between 2012 and 2020 found that more than 99.9 percent of the peer-reviewed scientific literature explicitly or implicitly endorsed anthropogenic causation, with only a handful of outlier papers dissenting. This level of consensus is comparable to that found in other well-established areas of science, such as the link between smoking and lung cancer.
Claims that current warming is primarily natural, driven by the sun, or too small an effect for a trace gas like CO2 to matter, have each been examined directly against observational data and found inconsistent with it. Satellite measurements of total solar irradiance show no meaningful upward trend since the 1980s, the period of most rapid warming, while some analyses suggest a slight cooling contribution from solar activity over recent decades. Climate models that include only natural forcings, such as solar variability and volcanic eruptions, reproduce the relatively stable pre-industrial climate reasonably well but fail to replicate the rapid warming observed after 1950; models that add human greenhouse gas emissions match the observed record closely, which is itself part of the evidence for attribution. The infrared absorption properties of CO2 and other greenhouse gases are established physics, verified in laboratory measurements dating back to the nineteenth century work of physicists including John Tyndall, independent of any climate model. Skeptical arguments have shifted over time as each prior objection was addressed by new data, moving from denying warming altogether, to attributing it to natural cycles, to more recently arguing that warming, while real and human-caused, will be modest or manageable without significant policy response. The IPCC's assessment reports specifically evaluate this range of scenarios and consistently find that continued high emissions carry substantially greater risks of severe and irreversible impacts than pathways involving rapid decarbonization.
Common claims
- Current climate change is driven by natural cycles, not humansNot supported, natural forcings cannot explain observed warming pattern
- Scientists disagree significantly about whether humans cause warmingFalse, 97-100% of actively publishing climate scientists agree
- The sun is responsible for recent warmingNot supported, solar output has not increased during the period of strongest warming
- CO2 is such a tiny fraction of the atmosphere it can't matterNot supported, CO2's infrared absorption properties are well-established physics