Nathaniel Tarshish, David M Romps, Inez Fung

Many human activities influence the climate, such as burning fossil fuels, clearing land, growing food, and using refrigerants. Among these, fossil fuels have long been considered the primary driver of global warming. Here, the impact of fossil fuels on historical warming is reassessed using a climate emulator ensemble that accounts for key uncertainties. This reveals that, until the 2020s, fossil fuels were likely not the main cause of warming. Moreover, before 1980, their net effect was likely cooling, as high rates of sulfate emissions from coal likely increased Earth’s reflectivity enough to offset the warming effects of the accumulated greenhouse gases due to fossil fuels. Agriculture and land use were instead the primary drivers of 20th-century warming. However, in recent decades, fossil-fuel warming has surged due to the accumulation of carbon dioxide and lower sulfate emissions. Fossil fuels are now responsible for approximately half of present-day global warming.