WASHINGTON — Climate change may be making day to day life hotter (and possibly sunnier), but a new study reveals it’s also making Earth a darker planet. Researchers with the American Geophysical Union say warming ocean waters are causing a drop in the brightness of the planet.
After measuring 20 years of earthshine — the light from the Sun which Earth reflects and illuminates the Moon’s surface — the team discovered a noticeable drop in Earth’s reflectance (or albedo). The drop equates to about half a watt less light per square meter compared to light Earth was reflecting two decades ago. Researchers add most of that decline has come within the last three years.
Earth reflects about 30 percent of the sunlight that shines on it. The findings estimate that Earth’s reflectance has dropped by 0.5 percent during this study.
“The albedo drop was such a surprise to us when we analyzed the last three years of data after 17 years of nearly flat albedo,” says lead author Philip Goode, a researcher at New Jersey Institute of Technology, in a media release.
The Big Bear Solar Observatory in Southern California found that earthshine data from 1998 to 2017 had remained relatively unchanged. However, when scientists factored in the last three years, a clear trend emerged showing the decline.
How is climate change contributing to this?
Researchers say two things affect the amount of sunlight reaching Earth. One is the Sun’s brightness and the other is the planet’s own reflectivity. Study authors say the change in Earth’s albedo did not show a link to normal changes in the Sun’s brightness over time. This leaves Earth’s ability to properly reflect sunlight as the leading cause.
The team explains that climate change leads to fewer bright, reflective low-lying clouds in the air. Researchers detected a drop in these clouds over the eastern Pacific Ocean in the last few years, thanks to satellite measurements by NASA’s Clouds and the Earth’s Radiant Energy System (CERES).
That same region is where scientists are noticing higher sea surface temperatures due to a reversal of a weather condition called Pacific Decadal Oscillation. The researchers believe this reversal has a link to global climate change.
Study authors adds that the dimming of the Earth can also be seen through the amount of solar energy the planet is capturing in its climate system. Once this energy enters the atmosphere and oceans, it can contribute to global warming and higher temps.
“It’s actually quite concerning,” says Edward Schwieterman, a planetary scientist at the University of California at Riverside who did not take part in the study.
Scientists hoped that a warmer Earth may actually lead to more clouds and a brighter planet.
“But this shows the opposite is true,” Schwieterman concludes.
The findings appear in the journal Geophysical Research Letters.