Fact brief – Did CO2 contribute to early 20th century warming?
Posted on 15 July 2025 by Sue Bin Park
Skeptical Science is partnering with Gigafact to produce fact briefs — bite-sized fact checks of trending claims. You can submit claims you think need checking via the tipline.
Did CO2 contribute to early 20th century warming?
Warming from 1920 to 1940 was influenced by both natural dynamics or “forcings” as well as human-caused greenhouse gas emissions such as CO2.
Human-caused CO2 began rising during the Industrial Revolution and contributed to early 20th century warming. At the same time, solar activity rose slightly and volcanic activity was unusually low, adding to warming. Ocean circulation changes also raised regional temperatures in areas like the North Atlantic.
The myth that early warming disproves CO2’s role in climate change ignores that scientists account for all major forcings. Studies estimate that without human emissions, only about half the early 20th-century warming would have occurred.
Since 1975, solar activity has declined and volcanic eruptions have cooled the atmosphere, yet global temperatures have surged alongside the steep rise in greenhouse gas emissions. Only models that include CO2 match observed warming trends. Natural variability alone cannot explain the industrial era increase in global temperatures.
Go to full rebuttal on Skeptical Science or to the fact brief on Gigafact
This fact brief is responsive to quotes such as this one.
Sources
NOAA Climate Change in the Context of Paleoclimate
NASA Carbon Dioxide
Wiley Interdisciplinary Review Climate Change The early 20th century warming: Anomalies, causes, and consequences
NASA The Causes of Climate Change
About fact briefs published on Gigafact
Fact briefs are short, credibly sourced summaries that offer “yes/no” answers in response to claims found online. They rely on publicly available, often primary source data and documents. Fact briefs are created by contributors to Gigafact — a nonprofit project looking to expand participation in fact-checking and protect the democratic process. See all of our published fact briefs here.
