Earth is not as bright as it used to be

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They discovered that the Earth is not as bright as it used to be and that it has faded at a noticeable rate in recent years.

Using a telescope that doesn’t look much different than the one you might have at home, researchers at the Big Bear Solar Observatory have been taking measurements every night for 20 years, to study the sun’s solar cycle. and cloud cover.

They did this by measuring the “earth’s brightness,” which occurs when “the dark side of the moon picks up the reflected glow of the earth and reflects that light back,” according to NASA. The amount of terracotta will vary from night to night and season to season.
“You are looking at a quarter moon. You can see the entire moon because three quarters are illuminated by that ghostly light,” said Philip Goode, a researcher at the New Jersey Institute of Technology and lead author of the new study.

After 20 years of measuring “ghostly light,” they found it was fading.

“It’s actually the sunlight reflected off the earth, and that’s what darkens,” Goode said.

In fact, Earth now reflects about half a watt less light per square meter than it did 20 years ago, the equivalent of a 0.5% decrease in Earth’s reflectance. The Earth reflects about 30% of the sunlight that shines on it.

“A lot of those things, you can give up your common sense at the door and there are a lot of surprises,” Goode said. “It’s one of those surprises.”

For the first 17 years, the data seemed more or less the same, to the point that the researchers almost canceled the rest of the study.

“We were kind of reluctant to do the last three years of data because it had looked the same for 17 years, but ultimately we decided to do it because we had promised ourselves 20 years of data, so let’s do it, and we had the unexpected, ”Goode said.

In a shocking turn of events, the last three years of their study have shown that the earth’s luster has dramatically diminished. So much so, they thought their data was wrong.

This graph shows the average annual Earthshine in black from 1998 to 2017. The blue line shows the annual CERES albedo, which is another annual measure of the Earth's reflectivity, from 2001 to 2019. The black and blue dotted lines are the best fit lines showing that the reflectivity of the Earth has decreased over the past 20 years. Credit: Goode et al. (2021), Geophysical research letters

“When we looked at the data for the past three years, it looked different,” Goode said. “The reflectance had gone down and down noticeably. So we thought we had done something wrong. So we did it again a few times and it turned out to be correct.”

They noticed that the data did not correlate with the sun’s varying brightness due to its solar cycles, which meant the cause had to be something else.

What they noticed was a decrease in cloud cover. Sunlight bounces off cloud tops and is reflected back into space. When there is a decrease in cloud cover, more sunlight is allowed.

“The earth receives more heat because the reflected light is reduced, so it receives more sunlight, in the visible spectrum,” Goode said.

The largest decrease in cloud cover occurred on the western coasts of North and South America, the same region where sea surface temperatures rose due to a reversal of a climatic condition called Pacific Decadal Oscillation (PDO).
This graph shows the hot (red) and cold (blue) phases of the Pacific Decadal Oscillation (PDO). Earth is currently in a cold phase of PDO.
PDO is a term used to refer to long-term fluctuations in ocean temperature across the Pacific Ocean. As the ocean warms and cools in different places, this has a direct impact on the trajectory of the jet stream. This displacement of the jet stream has a direct impact on long-term weather and climate conditions, particularly on the western coasts of North and South America.

“Off the west coast of the Americas, the low clouds were scorched and more sunlight entered, so the way we saw it, the Earth’s reflectance went down,” Goode said.

Goode stopped before saying it would have a direct impact on warming the Earth faster. “Of course, Earth gets an extra half a watt per square meter, but what Earth chooses to do with that energy, we’d kind of be guessing.”

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