WashingtonWarming ocean waters have caused the Earth’s luminosity to drop, according to a study that found our planet now reflects about half a watt less light per square meter than it did 20 years ago.
The study, published in the journal Geophysical Research Letters, used decades of measurements of the Earth’s brightness – the light reflected from the Earth that illuminates the surface of the Moon.
The researchers also analyzed satellite measurements, finding that there has been a significant drop in the Earth’s reflectance, or albedo, over the past two decades.
They found that Earth is now reflecting about half a watt less light per square meter than it was 20 years ago, with most of the decline having occurred in the last three years of data on the brightness of the earth.
That’s the equivalent of a 0.5% decrease in Earth’s reflectance, according to the researchers.
The Earth reflects about 30% of the sunlight that shines on it, they noted.
“The decline in albedo surprised us so much when we analyzed the last three years of data after 17 years of near-flat albedo,” said Philip Goode, a researcher at the New Jersey Institute of Technology and lead author of the study. .
Goode was referring to the Earth’s brightness data from 1998 to 2017 collected by the Big Bear Solar Observatory in Southern California.
When the latest data was added to previous years, the tendency towards obscuration became clear, the researchers said. They noted that two things affect the net sunlight reaching Earth: the brightness of the Sun and the reflectivity of the planet.
The changes in Earth’s albedo observed by the researchers did not correlate with periodic changes in the Sun’s brightness, meaning that the changes in Earth’s reflectivity are caused by something on Earth.
There has been a reduction in bright, reflective low clouds over the eastern Pacific Ocean in recent years, according to satellite measurements made as part of the Clouds and the Earth’s Radiant Energy System (CERES ).
This is the same area where increases in sea surface temperatures have been recorded due to a reversal of a climatic condition with likely links to global climate change, the researchers said.
The darkening of the Earth can also be seen in terms of the amount of additional solar energy captured by the Earth’s climate system, they said.
Once this important additional solar energy is in Earth’s atmosphere and oceans, it can contribute to global warming, the researchers explained.
Indeed, the additional sunshine is of the same magnitude as the total anthropogenic climate forcing, or a number of human-induced factors, over the past two decades, they added.
“It’s actually quite concerning,” said Edward Schwieterman, a planetary scientist at the University of California at Riverside who was not involved in the study.
Many scientists were hoping that a warmer Earth could lead to more clouds and higher albedo, which in turn would help moderate warming and balance the climate system, he said.
“But it shows the opposite to be true,” Schwieterman added.
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