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The light reflected from Earth that illuminates the surface of the Moon—”Earthshine”—has waned in … [+]
Go look to the southwestern sky just after sunset this week and you’ll see something beautiful—a crescent Moon whose darkened side is subtly lit.
Catch it while you can because it’s getting dimmer—and all because of climate change, say scientists.
What you can see is “Earthshine,” sunlight that first strikes Earth before being reflected onto the Moon. It’s a delicate, ethereal sight that can most easily be see through binoculars, and even then only in the few nights either side of New Moon when our natural satellite appears in the night sky as a crescent.
Published in the AGU journal Geophysical Research Letters, a study of the light reflected from Earth that illuminates the surface of the Moon, as well as satellite measurements, have revealed a significant drop in Earth’s reflectance, or albedo, over the past two decades.
The culprit? Climate change.
Big Bear Solar Observatory
Measured from the Big Bear Solar Observatory in California between 1998 and 2017, the researchers monitored the precise daily, monthly, seasonal, yearly and decadal changes in Earth’s albedo using earthshine. They measured a gradual, but significant decline over the two decades of data.
That’s the equivalent of a 0.5% decrease in the Earth’s reflectance. Earth reflects about 30% of the sunlight that shines on it.
Could it be caused by solar activity, which fluctuates over an 11 year cycle? The researchers found no correlation, which means that changes in Earth’s albedo is caused by something on the Earth.
Earthshine annual mean albedo 1998–2017 expressed as watts per square meter (W/m2). The CERES annual … [+]
“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,” said Philip Goode, a researcher at New Jersey Institute of Technology and the lead author of the new study.
Their results were in line with earthshine fluctuations measured by the CERES satellite, which is part of the NASA’s Earth Observing System (EOS).
The reason? A reduction in bright, reflective low-lying clouds over the eastern Pacific Ocean in the most recent years of the data sample. It’s the same area where increases in sea surface temperatures have been recorded because of the reversal of a climatic condition called the Pacific Decadal Oscillation.
“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.
It had been hoped that a warmer Earth might mean more clouds and higher albedo, which would help to moderate warming and balance the climate system, said Schwieterman. “This shows the opposite is true.”
Wishing you clear skies and wide eyes.