Work published in the scientific journal Geophysical Research Letters They suggest that global warming is contributing to the darkening of the blue planet.
Working at the Big Bear Lake Solar Observatory in California, which specializes in studying the sun, astronomers have collected data every night for the past 20 years to study the solar cycle and cloud cover.
Half a watt of light per square meter
They obtained these results by measuring Earth’s light, which occurs when the dark part of the Moon picks up the glow reflected from Earth and reflects it back. The amount of illumination varies depending on the night and season of the year.
“When you look at a quarter of the moon, you can see the entire moon because three-quarters of it is illuminated by this ghostly light,” says Philip Good, a researcher at the New Jersey Institute of Technology and author of the groundbreaking new study.
Twenty years after measuring ghostly light, researchers have found that it is fading. Philip Good continues: “In fact, sunlight is reflected off the Earth, and that’s what darkens.”
The Earth now reflects half a watt of light per square meter than it did twenty years ago. This represents a decrease in reflectance, or the percentage of light reflected from the Earth, of 0.5% over this period. A significant drop as the Earth reflects about 30% of the light coming from the Sun.
Noticeable darkening over the past three years
For the first 17 years, the data collected at the American Observatory looked relatively similar. It wasn’t until three years ago that researchers noticed that the Earth’s brightness had greatly diminished, causing them to believe their conclusions were flawed.
“The reflection was significantly reduced, and we thought we had done something wrong,” explains Philip Goode, who then realized that the data was correct.
Low clouds less bright due to global warming
Unable to establish a relationship between their data and the sun’s changing luminosity due to its solar cycles, the researchers looked at the other factor: cloud cover. They notice a decrease in that due to climate change. Since sunlight bounces off clouds less, it happens to be reflected less back into space. So the blue planet is less bright.
This decrease in cloud cover, particularly on the western coasts of North and South America, causes sunlight to be absorbed by the sea and thus the Earth’s surface, causing it to warm. In other words, global warming leads to more global warming.
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