Our planet is getting dimmer, with less light reflected off Earth’s atmosphere onto the surface of the moon – and it could be a big problem.
Warming ocean waters have led to a drop in "Earthshine", the light reflected on to the moon, due to changes in cloud patterns.
Earth is now reflecting about half a watt less light per sq metre than it was 20 years ago, and researchers fear this could lead to it absorbing more energy from the sun, worsening climate change.
Most of the drop has occurred in the last three years, according to the study in the AGU journal Geophysical Research Letters.
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It’s the equivalent of an 0.5% decrease in Earth's reflectance or "albedo".
Earth reflects about 30% of the sunlight that shines on it.
Philip Goode, a researcher at New Jersey Institute of Technology and the lead author of the new study, said: "The albedo drop was such a surprise to us when we analysed the last three years of data after 17 years of nearly flat albedo.”
The researchers say there has been a reduction of bright, reflective low-lying clouds over the eastern Pacific Ocean in recent years, according to satellite measurements made as part of Nasa's Clouds and the Earth's Radiant Energy System (Ceres) project.
That's the same area, off the west coasts of North and South America, where increases in sea surface temperatures have been recorded because of the reversal of a climatic condition called the Pacific Decadal Oscillation.
Researchers believe this is connected to global climate change.
They fear the change will mean more solar energy is being captured by Earth's climate system.
Once this significant additional solar energy is in Earth's atmosphere and oceans, it may contribute to global warming.
"It's actually quite concerning," said Edward Schwieterman, a planetary scientist at the University of California at Riverside who was not involved in the new study.
For some time, many scientists had that a warmer Earth might lead to more clouds and higher albedo, which would then help to moderate warming and balance the climate system, he said.
Schwieterman said: "But this shows the opposite is true."
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