Earth’s ‘dirty mirror’ effect is accelerating climate change

New research shows that cloudy areas over oceans are reflecting less sunlight to space than before, adding to heating from rising greenhouse gas levels and causing climate change to accelerate.

The study, published today (Tuesday, 11 March) in Environmental Research Letters, found this dimming effect was occurring in several regions, including cloudy areas off the coasts of California and Namibia, but also at the fringes of Antarctica where recent significant melting of sea ice can also explain more absorption of sunlight by the oceans.

Professor Richard Allan, lead author of the study at the University of Reading, said: “Think of Earth as a mirror reflecting sunlight back to space. Over time, that mirror is getting dirtier, particularly over our oceans where clouds are changing. This means more solar energy is being absorbed rather than reflected, adding to the heating caused by greenhouse gas emissions. An important puzzle to solve is, are the clouds melting away as temperatures rise like a mirror steaming up? Or is declining air pollution that artificially brightened the mirror like a cleaning spray now wearing off? We need to find out which explanation is causing clouds to become less shiny to understand how much global warming will occur and how fast. The remarkable global dimming helps explain why we saw such unprecedented warming in 2023.”

Air pollution impacts

The researchers examined the warming that occurred in 2022 to 2023 and discovered the ocean surface warmed even more rapidly than could be explained by the increased energy absorption alone. This led them to the conclusion that either the heat was concentrated in a shallower layer of ocean than normal, or extra heat stored in deeper ocean layers was returning to the surface. The second explanation aligns with the development of El Niño conditions in 2023, when warm water from ocean depths rose to the surface in the Pacific.

The study also found that eastern China is reflecting less sunlight than expected, likely due to successful efforts to reduce air pollution. This finding is significant because while reducing air pollution improves public health, cleaner air also allows more sunlight to pass through the atmosphere and clouds to reach Earth’s surface, adding to the warming from increases in heat-trapping greenhouse gases. The research suggests that these reductions in aerosol particles over China could be influencing climate patterns beyond its borders, potentially affecting cloudiness and temperature patterns over the north Pacific region through atmospheric wind patterns.