By making clouds less reflective, reduced pollution may be inadvertently contributing to rising global temperatures.
First of all, a fact: the Earth is reflecting less sunlight and absorbing more heat than it did a few decades ago, and this is accelerating global warming beyond what climate models predict. Meanwhile, overall pollution is likely decreasing.
Temperatures recorded in 2023 and 2024 exceeded projections and scientists are trying to understand why the atmosphere is letting more solar radiation through. A study this Wednesday in Nature Communications presents a theory for the phenomenon.
The authors believe that the reduction in atmospheric pollution may have reduced the brightness of marine clouds — crucial elements in regulating global temperature. Between 2003 and 2022, clouds over the Northeast Pacific and North Atlantic have become nearly 3% less reflective per decade. According to researchers, around 70% of this change is due to decrease in aerosols — small particles suspended in the air that influence both the formation and composition of clouds.
Efforts to combat air pollution, notably by limiting emissions resulting from the burning of fossil fuels, have significantly reduced the presence of particles in the atmosphere. The trend is expected to continue as clean energy replaces oil and gas. However, While improving air quality, reducing pollution may be inadvertently contributing to rising global temperatures.
Despite everything, Sarah Doherty, principal investigator at the University of Washington’s Cooperative Institute for Climate, Ocean and Ecosystem Studies, highlights: “We don’t want to go back and repeal laws that saved lives”, quotes the .
Scientists already knew that low clouds over the ocean dissipate as temperatures rise, exposing the sea surface to sunlight and amplifying warming. They also knew that aerosols have a cooling effect, by reflecting solar radiation and making clouds brighter. For decades, this atmospheric “shield” partially masked the warming effect caused by greenhouse gases.
By analyzing 20 years of satellite data, researchers found that reduced aerosols lead to larger, heavier cloud droplets that precipitate more quickly, thus reducing the duration and range of clouds. “By cutting pollution, reflectivity is lost and the system heats up, allowing more solar radiation to reach the Earth,” explained the study’s lead author, Knut von Salzen.
New climate models, which better incorporate the relationship between aerosols and cloud droplet size, show that global warming may be being underestimated.
“Warming is advancing faster than we expected”alertou of salts.
In response, some scientists are studying experimental solutions, such as spraying seawater to increase the reflectivity of oceanic clouds. Until the technique is perfected, studies like this offer a new perspective on the role of clouds and aerosols in Earth’s energy balance and help refine predictions about global warming in the coming decades.
