Earth is dimming as the warmer oceans are causing fewer bright clouds to reflect sunlight into space, trapping more energy in our planet, a new study has warned.
Decades of measurements of earthshine - the light reflected from Earth that illuminates the surface of the moon - allowed the team from the New Jersey Institute of Technology to get a better picture of the impact of climate change.
They also made use of satellite measurements to discover that there has been 'a significant drop in Earth's reflectance', or albedo, over the past two decades.
The Earth is now reflecting about half a watt less light per square metre than it was 20 years ago, according to the researchers.
The team said that half the drop in light happened in the past three years, after 17 years of flat albedo, mainly due to fewer low-lying clouds over the Pacific Ocean.
Scientists had hoped that a warmer Earth caused by climate change would create more clouds, and a higher albedo to moderate the warming, but the opposite appears to be happening, which could accelerate climate change.
The team found that the Earth's reflectance had dropped by about 0.5 per cent in the past three years - now reflecting 29.5 per cent of all sunlight.
'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,' said Philip Goode, lead author.
He was referring to the earthshine data from 1998 to 2017 that had been gathered by the Big Bear Solar Observatory in Southern California.
When the latest data was added to the previous years, the dimming trend became clear to the team.
Two things affect the net sunlight reaching the Earth: the Sun's brightness and the planet's reflectivity.
The changes in Earth's albedo observed by the researchers did not correlate with periodic changes in the Sun's brightness, so that means changes in Earth's reflectiveness are caused by something on the Earth.
When looking for obvious changes in other observations that could result in this change in albedo, the team turned to NASA satellites.
Satellite measurements made as part of NASA's Clouds and the Earth's Radiant Energy System (CERES) project, revealed a reduction of bright, reflective low-lying clouds over the eastern Pacific Ocean in the most recent years.
That's the same area, off the west coasts of North and South America, where increases in sea surface temperatures have been recorded.
This increase is down to the reversal of a climatic condition called the Pacific Decadal Oscillation, with likely connections to global climate change.
The dimming of the Earth can also be seen in terms of how much more solar energy is being captured by Earth's climate system.
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