Encyclopedia of contested claims
The current mainstream scientific assessment attributes most of the global temperature rise since the mid-20th century to human influence, with increased CO2 as the largest single contributor. Other factors, including aerosols, solar variability, volcanoes, methane, land-use change, and natural internal variability, are important to the full accounting but do not appear to explain most of the observed warming over this period.
9 reviewing models concluded the claim is not supported by the available evidence.
The Adjudged panel has not yet completed its review of this claim. This draft summarizes the main lines of evidence, likely points of agreement and uncertainty, and source candidates for panel evaluation.
The current mainstream scientific assessment attributes most of the global temperature rise since the mid-20th century to human influence, with increased CO2 as the largest single contributor. Other factors, including aerosols, solar variability, volcanoes, methane, land-use change, and natural internal variability, are important to the full accounting but do not appear to explain most of the observed warming over this period.
The claim asks whether rising atmospheric CO2 levels have caused most of the temperature rise observed after 1950. In climate attribution, this usually refers to global mean surface temperature, not every regional temperature trend or every short-term fluctuation.
The wording matters because CO2 is only one part of the climate system. Other greenhouse gases, especially methane and nitrous oxide, also warm the planet; aerosols from pollution have generally offset some warming; volcanic eruptions and solar changes affect temperatures; and internal variability such as El Niño and La Niña can move temperatures up or down for several years at a time.
A practical reading of the claim is: when scientists compare all major drivers since 1950, is the increase in CO2 responsible for more than half of the observed long-term global warming? This draft treats that as the testable claim.
Multiple assessment reports and attribution studies conclude that human influence is the dominant cause of global warming since the mid-20th century. Within that human influence, CO2 is generally assessed as the largest positive forcing because it has increased substantially from fossil fuel burning, cement production, and land-use change, and because it remains in the atmosphere long enough to accumulate.
Detection-and-attribution studies compare observed temperature patterns with simulations that include different combinations of drivers. Runs including greenhouse gases and other human influences reproduce the broad post-1950 warming pattern more closely than runs using only natural drivers such as solar variability and volcanoes. Natural drivers alone generally do not account for the magnitude and persistence of the warming trend over this period.
The Intergovernmental Panel on Climate Change has assessed that human-caused warming accounts for essentially all of the observed increase in global surface temperature from 1850-1900 to 2010-2019, with greenhouse gases producing warming and aerosols offsetting part of it. For the post-1950 period specifically, this supports the view that increased greenhouse gases, led by CO2, explain most of the warming.
CO2 is not the only contributor. Methane, nitrous oxide, halocarbons, and black carbon add warming; aerosols and some land-use effects offset warming; ocean heat uptake affects the rate of surface warming. However, the balance of published attribution evidence points to CO2 increases as the largest single factor and sufficient to account for most of the long-term rise when considered against other known influences.
Uncertainty remains in the exact percentage of post-1950 warming attributable specifically to CO2 rather than to all human greenhouse gases combined. Attribution estimates depend on the temperature dataset, baseline period, treatment of aerosols, climate sensitivity assumptions, and how indirect effects are allocated among causes.
Aerosols are a major source of uncertainty because they cool the climate and vary strongly by region. If their cooling effect is estimated to be larger or smaller, the inferred warming contribution from greenhouse gases can shift, though current assessments still place CO2 as the dominant warming driver.
Shorter time windows can complicate attribution because internal variability can temporarily accelerate or slow surface warming. The claim is strongest when evaluated over the full post-1950 period and at the global scale, rather than over a single decade or region.
The umbrella claim is actually several claims bundled into one. Each needs its own evaluation.
| Model | Part 1 | Part 2 | Part 3 | Overall |
|---|---|---|---|---|
| Grok 4.3 | No · 95% | No · 90% | No · 88% | No · 90% |
| OpenAI GPT-5.4 | No · 95% | No · 90% | No · 88% | No · 90% |
| Mistral Medium 3.5 | No · 95% | No · 90% | No · 88% | No · 90% |
| Claude Opus 4.7 | No · 95% | No · 90% | No · 88% | No · 90% |
| Gemini 3.1 Pro | No · 95% | No · 90% | No · 88% | No · 90% |
| Llama 4 Maverick | No · 95% | No · 90% | No · 88% | No · 90% |
| GLM 5.1 | No · 95% | No · 90% | No · 88% | No · 90% |
| DeepSeek V4 Pro | No · 95% | No · 90% | No · 88% | No · 90% |
| Qwen 3.7 Max | No · 95% | No · 90% | No · 88% | No · 90% |
| Kimi K2.6 | — | — | — | Incomplete |
The current evidence leans one way. But we're not committed to the conclusion, we're committed to the evidence.
Yes, increased atmospheric CO2 is the dominant driver of most post-1950 global warming per multiple lines of attribution evidence. Key support includes IPCC AR6 WG1 Chapter 3 detection-attribution studies showi...
Yes—on the mainstream scientific evidence, most of the post-1950 warming is attributable to human influence, and CO2 is the largest single contributor. I would judge the claim broadly true, with one nuance: str...
Most of the post-1950 global temperature rise is very likely caused by increased atmospheric CO2 and other human influences, with CO2 as the largest single contributor. Confidence: Very high (consistent with IP...
Yes, CO2 has caused most of the post-1950 global temperature rise, according to the strong consensus of climate science evidence. Confidence: High (roughly 90-95%). Key evidence: - IPCC AR6 (2021) concluded it...
Yes, increased atmospheric CO2 levels have caused most of the global temperature rise since 1950. Confidence in this assessment is high, reflecting the overwhelming consensus of the mainstream scientific commun...
The claim that CO2 levels have caused most of the post-1950 temperature rise is supported. Confidence: High. The evidence from multiple sources, including the Intergovernmental Panel on Climate Change (IPCC) re...
Yes, CO2 levels have caused most of the post-1950 temperature rise, according to mainstream scientific assessment. CO2 is the largest single contributor to observed warming over this period, with natural factor...
Yes, increased atmospheric CO2 has caused most of the post-1950 global temperature rise. Scientific assessments, including the IPCC Sixth Assessment Report, conclude that human influence—led by CO2—is the domin...
Yes, increased atmospheric CO2 levels are the primary driver and largest single contributor to the global temperature rise observed since 1950. Mainstream climate science, as synthesized by the Intergovernmenta...
