A study that used nearly 20 years of data indicates that Earth is becoming dimmer, and climate change is the likely culprit.
Earth reflects around 30% of the sunlight that hits the planet, and according to the researchers who published the paper in the peer-reviewed journal Geophysical Research Letters, Earth's albedo, or reflectance, has reduced. Researchers used data from 1998 to 2017 to measure the amount of Earthshine that causes the Moon to be illuminated and found that it has reduced by half a watt less light per square meter, or 0.5% when compared to data recorded in 1998.
According to theoretical physicist Philip Goode from the New Jersey Institute of Technology, "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 study found that the likely culprit of the reduction in reflectance is not due to a reduction in sunlight coming from Earth, but a reduction in the number of reflective clouds that appear over the eastern Pacific Ocean. The researchers link the reduction in these clouds to climate change.
The researchers wrote, "[Earth's albedo] is an essential determinant of the earth's climate, since, in the broadest sense, changes in climate arise from the simultaneous evolution of the solar intensity, the Earth's albedo, and greenhouse insulation." Adding, "Stringent data quality standards were applied to generate monthly and annual means. These vary significantly on monthly, annual, and decadal scales with the net being a gradual decline over the two decades, which accelerated in the most recent years."
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