Earth gets brighter every year but progression is volatile, study finds

Earth continues to get brighter every year, researchers have found, but the location and intensity of the progression has become increasingly volatile because of Covid-19, regulations on light pollution, and a faltering global economy.

Nasa-funded researchers at the University of Connecticut (UConn) studied more than 1.1m satellite images taken over a nine-year period to establish that the planet’s artificial light increased by a net 16% between 2014 and 2022.

The figure is in keeping with a 2017 study that found Earth’s artificially lit outdoor areas grew by 2% annually over the previous five years, and that light pollution encroached on darkness almost everywhere.

The difference in the latest study, published this month in Nature after peer review, is the finding that some parts of the planet became dimmer, helping to offset a 34% overall rise in global radiance.

Europe dimmed significantly due to efficiency regulations, the researchers said, while Venezuela lost more than 26% of its night-time light due to economic collapse.

More generally, lockdowns, a slowdown in industrial activity and reduced tourism caused by the coronavirus pandemic also had an impact in many areas during the early years of the decade; and more recently, the Ukraine-Russia war left “visible signatures” in that region.

Asia, unsurprisingly, continued to lead all regions in brightening.

“What satellites now reveal about our nights is not a tidy narrative of progress or decline,” Zhe Zhu, the study’s co-author and director of UConn’s Global Environmental Remote Sensing Laboratory, said in a report posted to Nasa’s website.

“It is a dynamic portrait of a species reshaping its environment in real time, building, destroying, conserving, and collapsing, often all at once. The world is not simply getting brighter. It is flickering.”

Zhu and his team analyzed the 1.16m satellite images pixel by pixel, filtering out interference from moonlight, clouds and atmospheric effects to allow in an approach he said was like using smart glasses to detect real changes in night-time light.

The experience was, he said, “like watching the heartbeat of the planet”.

Led by chief researcher Tian Li, Zhu’s team spent months looking at the images taken at approximately 1.30am local time every day of the nine-year study period by Nasa’s Visible Infrared Imaging Radiometer Suite. The brightening and dimming can be seen in a number of visualizations by the space agency.