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.