New research shows that the Earth’s albedo affects our overall cloud cover which has a large impact on light absorbed rather than reflected from the Earth.
“The reflectivity of the Earth is mainly a story of clouds,” says Philip Goode, a physics professor at the Big Bear Solar Observatory.
Goode and his colleagues were examining data gathered from 1998 to 2017. They examined both satellite measurements of the Earth and the amount of light reflected off the surface of the Earth onto the moon and back, called earthshine.
The study found that on average, the Earth reflects about half a watt less light per square meter than it did 20 years ago.
The dimming of the Earth did not correspond to the natural changes in brightness of the sun. The researchers wouldn’t have noticed this dimming if they hadn’t looked at the full 20 years of data. Part of the reason is because of periodic climate fluctuations known as the Pacific Decadal Oscillation.
Thanks to the precision of the NASA Clouds and the Earth’s Radiant Energy System (CERES) project, a satellite that measures the Earth’s radiation and cloud cover, the researchers could tell that the ocean was warmer off the West Coast of the Americas at the end of the study period in 2016-2017.
Corresponding with the warmer waters, the cloud cover over the Pacific off the American West Coast declined on average. “The clouds overhead seemed to disappear,” says Goode.
It is unclear how this is happening. It could be that more of the sunlight coming in gets absorbed by the ocean. It is also unclear as to what happens to the extra watt of light per square meter that is no longer reflected by the Earth. It could be part of the reason the Earth is experiencing global warming as reflectivity is one of the main things controlling our climate. “More heat is coming in, less is being reflected,” says Goode.
Some scientists hoped that a warming climate might result in more cloud cover, and therefore more reflectivity but this study shows the opposite.
https://www.discovermagazine.com/environment/warm-waters-are-causing-the-earth-to-dim