Warming oceans cause fewer bright clouds to reflect sunlight into space – trapping even more energy in our planet, study warns.
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.
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.
This matches the findings of a NASA study published in June, that found the Earth’s energy imbalance had doubled from 2005 to 2019.
This means more energy is being absorbed from the Sun than is reflected back to space, throwing the Earth’s energy ‘out of balance’ and warming the planet.
‘It’s actually quite concerning,’ said Edward Schwieterman, a planetary scientist at the University of California at Riverside who was not involved in the new study.
For some time, 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.’