A new scientific study, based on satellite images, has revealed that artificial nighttime lights increased the brightness of planet Earth by 16% between 2014 and 2022.
But this increase has not been uniform throughout the world; there are regions moving in the opposite direction, either because of wars and natural disasters, or because of successful policies to combat light pollution and rationalize energy consumption.
For centuries, Earth appeared from space as a completely dark sphere. Today, the pervasive lights reveal the progress of civilization and the expansion of electricity grids. But this constant light has become an environmental and health problem, affecting the quality of human sleep, disrupting the biological rhythms of plants and animals, and even obscuring our view of the universe and stars.
According to Chu Chu, a professor of remote sensing at the University of Connecticut and the lead author of the study, the Earth is not gradually and steadily brightening, but rather "flickering." While developing countries like India, China, and parts of Africa are experiencing a significant increase in light due to urbanization and rural electrification, areas of darkness are expanding year after year at an accelerating rate.
Some of this blackout comes suddenly due to wars and natural disasters, while some of it is gradual and deliberate due to government policies, as is the case in Europe.
For example, in France, light pollution has decreased by a staggering 33% as a result of new energy-saving and dark-sky policies. Meanwhile, the United States continues to experience an increase in light pollution in most areas, particularly on the West Coast.
This study is unique in that it is the first to reveal trends in artificial light usage with a high degree of temporal detail, enabling researchers to observe the COVID-19 lockdowns in satellite data and monitor the stages of armed conflicts in near real-time. "In Palestine," says Chu, "you can see the drops in light as the war intensifies. You can also see natural disasters, like the effects of hurricanes in Puerto Rico, which wipe out electricity for extended periods."
The team used data from NASA's Black Marble instrument, which employs special algorithms to filter out noise such as moonlight reflections, auroras, and cloud shadows. However, the researchers caution that the figures may not tell the whole story, as the sensors used are not sensitive to the blue light emitted by most modern LED lights. This leads to a significant paradox: when a city replaces its old streetlights with white LEDs, humans perceive the area as brighter, while satellites interpret it as dimming.
In this context, Christopher Kyba, a professor of remote sensing from Ruhr University in Germany and one of the study's participants, explained that human night vision is very sensitive to blue light, while satellite devices do not see it, creating a gap between what humans see and what technology records.
Kaiba had led a previous study in 2023, based on more than 50,000 human observations, which revealed that the brightness of the night sky as seen by humans is increasing at an astonishing rate of up to 10% per year, effectively erasing the stars from the night sky.
But Cho rejects the notion that brightness is solely a negative sign. He points out that lights in underdeveloped areas of Africa and Asia signify economic prosperity and the arrival of electricity to places that were once shrouded in darkness.
He concludes by saying: "From an economic perspective, brightness can be a good thing. It means more activity, and people having access to energy where it wasn't available to them before."
The study was published in the scientific journal Nature on Wednesday, April 8.
