Satellite data shows Earth is getting ever brighter at night

By Will Dunham

WASHINGTON, April 8 (Reuters) – Daily satellite observations have revealed continued nighttime brightening globally due to artificial lighting, with significant regional variations including an increase in sub-Saharan Africa and Southeast Asia, as well as deliberate dimming in Europe driven by concerns about energy conservation and light pollution.

The researchers documented a net 16% increase in global nighttime light between 2014 and 2022, but showed that it was not a constant brightening but rather a mosaic of increases and decreases in regional brightness shaped by many factors. In 2022, the United States had by far the highest total brightness of any country, followed by China, India, Canada, and Brazil.

The brightening was found to be mainly due to rapid urbanization, infrastructure expansion and rural electrification.

The dimming, however, had two very different drivers. Abrupt attenuation was usually caused by natural disasters, power grid failures and armed conflicts. Gradual dimming was often deliberate, driven by government regulations, transitions to energy-efficient LED lights, and efforts to reduce light pollution.

“For decades, we held a simplified view that the Earth at night was getting brighter and brighter as human populations and economies grew,” said Zhe Zhu, a professor of remote sensing and director of the Global Environmental Remote Sensing Laboratory at the University of Connecticut, lead author of the study published Wednesday in the journal Nature.

“We found that Earth’s nighttime landscape is actually very volatile,” Zhu said. “The planet’s light footprint is constantly expanding, contracting and changing.”

The researchers used more than a million daily images obtained by a U.S. government Earth observation satellite and processed by NASA. Previous global studies relied primarily on annual or monthly composite satellite images.

The most dramatic improvement has occurred in emerging economies, particularly sub-Saharan Africa and Southeast Asia. It was led by Somalia, Burundi and Cambodia, followed by several African countries, including Ghana, Guinea and Rwanda.

“It’s not just about urbanization. It’s about a massive expansion of energy access,” Zhu said. “These numbers represent a profound shift as entire regions move from near-total obscurity to integration into the global power grid.”

Massive losses of light have occurred in countries such as Lebanon, Ukraine, Yemen and Afghanistan, where light has fallen victim to armed conflict and collapsing infrastructure. Similar declines were observed “in Haiti and Venezuela, where the decline was more closely associated with prolonged economic crises and unreliable energy supplies.”

“In Ukraine, we observed a sharp and sustained decrease in light that perfectly matches the escalation of the conflict in February 2022,” when Russia launched a full-scale invasion, Zhu said.

“We see a similar sudden darkness descending on regions of the Middle East during times of conflict,” Zhu said.

Europe has seen a net 4% decrease in nighttime light radiation, largely due to technological advances and environmental policies.

“This is due to the widespread shift from older, less efficient street lights, such as high-pressure sodium lamps, to newer directional LED systems, as well as strict national energy efficiency mandates and dark sky conservation efforts,” Zhu said. “Europe is fascinating because it has a “very structured gradation model.”

Zhu called France a global leader in dark sky conservation and energy efficiency mandates.

Study co-author Christopher Kyba, professor of night light remote sensing at Ruhr University Bochum in Germany, added: “The dimming in France that has occurred due to deliberate decisions to turn off street lights late at night when there is no activity on the streets is extraordinary. It will be very interesting to see how this develops over time, and whether this practice extends beyond France.”

The United States saw a net increase in light of 6% during the study period.

“Geographically, the United States offers a microcosm of this global light complexity. The West Coast has largely brightened, consistent with population growth and dynamic technology economies. However, much of the East Coast and Midwest has actually dimmed. This is due to the dedensification of older urban centers, the decline of some manufacturing sectors, and the aggressive adoption of smart, energy-efficient city lighting programs like those in Washington, D.C. and Chicago,” Zhu said.

Large-scale lighting began with gas lamps in cities in the early 19th century, followed by electric lighting later that century – and has seen a relentless increase ever since. Cities and towns glow at night, obscuring many of the stars that once shone above.

“Light pollution has profound ecological consequences, disrupting nocturnal ecosystems, animal migrations and human circadian rhythms,” Zhu said.

(Reporting by Will Dunham, editing by Rosalba O’Brien)