Light pollution continues to increase. This is nothing new; Earth’s nights have been getting brighter for some time now. But a new study published in Nature, which confirms this trend, has also found that artificial light is receding in parts of the planet. In some areas, this is due to conflicts or crises, such as in Ukraine, Syria, or Venezuela. But in others, such as Europe, thanks to technological transition and increased awareness of the damage this pollution causes to ecosystems and humans themselves, the night is recovering.
Using 1.16 million images captured by three different satellites, researchers from NASA and several universities have confirmed that the Earth is brighter than ever before. According to the instrumentation used in the Black Marble project, artificial light captured from space has increased by 16% since 2014. But behind this net increase lies another reality: during the same period, there have been areas of the planet where light radiance (measured in watts per square meter) has decreased.
“We can consider these dynamics as the heartbeat of society,” says Zhe Zhu, director of the Global Environmental Remote Sensing Laboratory at the University of Connecticut and lead author of the study. “With this daily data, we can observe the impact of crises. We see how society responds to major disruptions,” Zhu adds. “Decreased daylight isn’t always a sign of poverty or decline; sometimes, as we see in Europe, it’s a sign of adaptation and of government policies working in real time.”
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Evolution of nighttime illumination from 2014 to 2022
The animation shows the evolution of nighttime illumination between 2014 and 2022.Video: Kel Elkins/NASA’s Scientific Visualization Studio
Western European countries are among those that have reduced their nighttime lighting, and they have done so gradually. “It’s a sign of technological maturity and environmental awareness, driven by energy-saving mandates and the transition to better-targeted LED systems,” Zhu explains in an email. Overall, artificial light radiance has decreased by 4% in Europe since 2014. France stands out with a 33% reduction in nighttime lighting, followed by the UK with a 22% decrease. “In Spain, the net change in radiance is -52.444 [measured in nanowatts per cm²], with a brightness increase of 71.687 and a decrease of -124.131,” Zhu details.
But where light pollution has decreased the most is precisely where everything else has decreased. “In our study, regions like Syria (-95%), Ukraine (-75%), and Venezuela (-26%) show the most drastic dimming, as light is often a victim of conflict and systemic collapse,” explains the University of Connecticut researcher. In contrast, the dimming caused by government policies is more structured and gradual. “While the percentage decrease in Europe is smaller than in a war zone, it represents an intentional and much more widespread change in how developed societies interact with the night,” Zhu concludes.
Among the inhabited parts of the world where nighttime lighting has increased the most are several regions of India and China. In these countries, expansive industrial development, rapid urban growth, and the increasing electrification of rural areas are all contributing factors. Something similar is occurring throughout Southeast Asia. Among the most brightly lit areas, which contrast sharply with the surrounding deserts, are the cities of the Middle East. Although mitigated, nighttime lighting continues to reflect the divide between rich and poor countries.
“The relationship between per capita light emissions and per capita GDP is quite strong within a country, but not directly comparable between countries,” notes Christopher Kyba, professor of nighttime light remote sensing at Ruhr University Bochum (Germany) and co-author of the study. “Currently, these relationships hold; however, if we imagine a future in which cities are illuminated more sustainably, the relationship between nighttime light emissions and wealth is likely to break down at some point,” he adds.
The map shows lighting trends in Europe and parts of Africa and Asia. Blue indicates areas where lighting has decreased since 2014. Yellow indicates areas where it has increased. The white areas, such as the Nile Delta and the Cairo metropolitan area, show both trends occurring simultaneously.Tian Li y Zhe Zhu/University de Connecticut
Kyba has been researching light pollution since 2009. He must have been among the first to warn that excessive light pollution threatened to obscure the stars, disrupt animal life — even affecting birdsong — and harm human health, damaging melatonin production, for example. He always cautioned against the increase in artificial light. “Previous studies generally focused on the national or continental scale. Therefore, they observed a generalized increase, and the new study agrees with that conclusion,” the professor recalls. “The novelty lies in the fact that we analyzed what happens on much smaller spatial [and temporal] scales. We discovered that it is not a constant process of increase, but rather a simultaneous increase and decrease within countries that, as a whole, experience more brightness,” he now acknowledges.
However, Kyba fears that much of the light is escaping the satellites’ view. “Part of the dimming is due to an unfortunate instrumental design flaw: the satellite doesn’t observe the same wavelengths of light as the human visual system, so the longer wavelength changes (orange and infrared light) from the high-pressure sodium lamps to the white light of the LEDs are often registered as decreases in light by the instrument, even though a person would probably say the area brightened,” he explains.
The main criticism leveled by Alejandro Sánchez de Miguel, from the Department of Earth Physics and Astrophysics at Complutense University of Madrid, who was not involved in this study, is technological. “These satellites don’t see blue light, which is the most polluting part of the spectrum, but they do see infrared,” Sánchez de Miguel points out. “We have sodium lamps, for example, which emit a lot of infrared and none of blue light, and thus contribute to some pollution. And we have the opposite: LEDs, which pollute a lot of blue light and none of infrared. When a switch is made from sodium to LED, the satellite detects a decrease, but it’s a false one,” he explains.
Even so, Sánchez de Miguel acknowledges the contribution of this new work: “It shows how dynamic the issue of light pollution is.” But he ends by lamenting the lack of a European satellite measuring nighttime illumination and the need to rely on space photography, “like the images taken by the Artemis astronauts, who have seen what the illuminated night is really like.”
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