Earth is becoming dimmer, reflecting less and less light due to climate change, which is reducing shiny cloud cover in key areas, a new study has found.
Researchers studied years of data, including satellite measurements, and found that Earth’s reflectivity, known as albedo, has dropped significantly over the past two decades.
As a result, there has been a drop in earthshine, the light reflected from Earth that faintly illuminates the moon when it is otherwise hidden from the direct rays of the sun, each month just before a new moon.
“The Earth is now reflecting about half a watt less light per square meter than it was 20 years ago, with most of the drop occurring in the last three years of earthshine data,” the researchers found, according to a statement last week from AGU Journals, a geophysical website that published the paper at the end of August.
That is a 0.5 percent drop in reflectivity for Earth, which reflects about 30% of the sunlight that shines on it, according to the study.
Researchers analyzed data gathered by the Big Bear Solar Observatory in Southern California from 1998 to 2017, along with more recent measurements over the past few years.
“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,” the lead author of the study, Philip Goode, a researcher at the New Jersey Institute of Technology, said in the statement.
The amount of light reflected by Earth is affected by the net sunlight that reaches the planet and its reflectivity. The changes in albedo did not match up with periodic changes in the brightness of the sun, leading researchers to conclude it was something about Earth itself that had been altered.
In particular, there has been a reduction in bright, reflective low-lying clouds over the eastern Pacific Ocean, according to data gleaned from satellites that are part of NASA’s Clouds and the Earth’s Radiant Energy System.
An increase in sea surface temperature has been recorded in the same area off the west coast of the American continent due to a reversal in the Pacific Decadal Oscillation, a regional climate cycle that has been linked to global climate changes.
Edward Schwieterman, a planetary scientist at the University of California at Riverside, who did not participate in the study, said that the findings are “quite concerning” as many scientists had hoped that warming conditions on Earth would generate more clouds and so increase albedo, which would then contribute to moderating the warming process, balancing the climate.
“But this shows the opposite is true,” Schwieterman said in the AGU Journals statement.