Earth gets darker; why the planet appears dimmer from space
AUSTIN (KXAN) — The Earth is getting darker; the planet itself, when viewed from space, appears darker than it did in the past. The upper half actually appears to be getting darker than the bottom half.
New research published this fall in PNAS used two decades of observations from NASA’s Clouds and the Earth’s Radiant Energy System (CERES) satellite to learn more about what’s happening.
“(The records) show that there’s an increase in how much energy we get into the Earth system compared to how much is going out of the Earth system,” said Oivind Hodnebrog, a senior researcher at Norway’s Center for International Climate Research to the Associated Press.
Essentially, Earth is absorbing more energy than it is releasing. As a result, the Earth is getting warmer as well.
“It’s a bit like having a black T-shirt on a summer day. You get warmer because you absorb more sunlight because it’s a dark T-shirt. If you have a white T-shirt, more of the sunlight is reflected away, so then it’s lighter, less dark. It’s a bit the same,” Hodnebrog said.
What is causing the darkening?
There are a few factors believe play a role, according to the report.
One factor is the Earth’s air is cleaner than it was in the 1950’s, when we first started observations of Earth from space. Aerosol pollution has dropped off. Aerosols, made of tiny particles, used to bounce more sunlight back into space.
Melting sea ice is also playing a role. White ice is very good at reflecting light back into space. As the planet has warmed, glaciers in the arctic have melted. According to the study, sea ice melt is more concentrated in the northern hemisphere, explaining the difference in the dimming between the north and south.
Finally, cloud cover has decreased over the last few decades. Aerosols can act as seeds for clouds. Fewer aerosols means less clouds.
“When you have aerosol pollution, it makes the clouds brighter, which leads to a cooling. And again, when you clean up the aerosols, the clouds also get darker, and that’s a major effect,” Hodnebrog said.
A 2024 study by the National Oceanic and Atmospheric Administration (NOAA) revealed that cleaning up our shipping industry and reducing emissions by boats has led to fewer clouds in the sky.
“While reducing sulfur emissions is crucial for improving air quality and public health, it also eliminates the cooling effect that had been offsetting some of the warming caused by greenhouse gases,” according to NOAA.
