According to a study, warming ocean waters have led to a drop in Earth’s brightness.

Our planet now reflects about half a watt less light per square metre than it did 20 years ago, with most of the drop occurring in the last three years of Earthshine data.

As part of the study, published in the journal Geophysical Research Letters, researchers used decades of Earthshine measurements to come up with their conclusion. Earthshine is the light reflected from the Earth that illuminates the surface of the moon.

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Researchers estimate that the decrease in reflected light is the equivalent of a 0.5 per cent decrease in the Earth’s reflectance.

According to the researchers, Earth reflects about 30 per cent of the sunlight it receives.

Philip Goode, a researcher at the New Jersey Institute of Technology and the lead author of the study, says 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,”.

In his statement, Goode is referring to the Earthshine data gathered by the Big Bear Solar Observatory in Southern California from 1998 to 2017.

The researchers said the dimming trend became apparent when the latest data was added to the previous years.

They noted that solar brightness and the planet’s reflectivity are two features that affect the amount of net sunlight reaching the Earth.

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Observations by the researchers did not correlate with the periodic changes in the Sun’s brightness, meaning something on Earth is responsible for changes in Earth’s reflectiveness.

According to NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project, there has also been a reduction in bright, reflective low-lying clouds over the eastern Pacific Ocean in recent years.

That is the same area where increases in sea surface temperatures have been recorded because of the reversal of a climatic condition with likely connections to global climate change, according to the researchers.

According to them, the dimming of the Earth is also evident in how much more solar energy is being captured by Earth’s climate system.

According to the researchers, this additional solar energy can contribute to global warming once it reaches Earth’s atmosphere and oceans.

“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 had hoped that a warmer Earth might lead to more clouds and higher albedo, which would then help to moderate warming and balance the climate system, he said.

“But this shows the opposite is true,” Schwieterman added.

(With inputs from agencies)