Here's why the Earth isn't as bright as it once was
Tuesday, 5 October 2021
The Earth isn't as bright as it once was, and has been dimming at a noticeable pace for years, researchers say.
Why? Well, it appears the lack of shine from our planet is due to climate change.
Scientists from the Big Bear Solar Observatory in California have been studying the Earth and taking measurements of the Sun's solar cycle and cloud cover for the past 20 years.
They observed the phenomenon known as “earthshine”, which, as Nasa explains, occurs when the dark face of the Moon catches Earth's reflected glow and returns that light.
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Earthshine varies in strength throughout the year, since the light reflected from the Earth varies.
A new study, published in the AGU journal Geophysical Research Letters, found there had been a significant drop in Earth’s reflectance, or albedo, over the past two decades.
The Earth now reflected about half a watt less light per square metre than it did 20 years ago, with most of the drop occurring in the past three years, the researchers said.
Lead study author Philip Goode, a researcher at the New Jersey Institute of Technology, said in a statement that “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 observed changes in the Earth’s albedo didn’t correlate with periodic changes in the Sun’s brightness, which meant it was caused by something else. The scientists then noticed a decrease in bright, reflective cloud cover over the eastern Pacific Ocean in recent years – specifically the west coasts of North and South America.
When there's a lot of cloud cover, sunlight is reflected back into space, but when there’s less cloud, more sunlight is allowed through.
The noticeable change in cloud cover was over the same area where increases in sea surface temperatures had been recorded, the researchers noted.
“The recent drop in albedo is attributed to a warming of the eastern Pacific, which is measured to reduce low-lying cloud cover and, thereby, the albedo,” the scientists wrote in their study.
“It’s actually quite concerning,” Edward Schwieterman, a planetary scientist at the University of California, said.
Scientists had hoped a warmer planet would lead to an increase in clouds and higher albedo, which would then help to moderate warming and balance the climate system, he said in a statement.
“But this shows the opposite is true.”