image: This is a graph of changes in artificially lit surface of Earth at night. view more
Credit: Carla Schaffer / AAAS
Artificial Lights Increasing "Loss of Night," Especially in Some Nations: In a long-term, high-resolution global analysis of night light emissions, researchers report that the artificially lit surface of our planet is still growing - in both size and brightness - in most countries. In fewer countries has it stayed stable or declined, they say. Notably, the growth in nighttime light from 2012 to 2016, the period these researchers evaluated, nearly matched the global rise in gross domestic product (GDP), suggesting access to solid-state lighting does not decrease global energy consumption for outdoor light, as has been the goal. Artificial light is an environmental pollutant that threatens nocturnal animals and affects plants and microorganisms. During the second half of the 20th century, artificial outdoor light grew steadily, prompting inquiry into whether that trend will continue. To investigate whether the use of outdoor light is continuing to grow exponentially, Christopher Kyba and colleagues studied data gathered by the Visible Infrared Imaging Radiometer (VIIRS), a satellite sensor with a spatial resolution of 750 meters. Results demonstrated that Earth's artificially lit outdoor areas grew by 2.2% per year, from 2012 to 2016. Lighting changes varied greatly by country, far exceeding the global rate in some cases, and with decreases in radiance in only a few (such as Yemen and Syria, both experiencing warfare). In some of the world's brightest nations, like the United States and Spain, radiance remained stable, while for most nations in South America, Africa and Asia, it grew. Taken together, and despite a few examples of decreases in radiance, the results suggest that the global demand for outdoor nighttime light has not been met yet; decreases in related energy consumption appear unlikely, even as the solid-state lighting revolution had hoped to lessen them. Notably, the authors point out, VIIRS only detects light emitted between 500 and 900 nanometer (nm) wavelengths. It does not "see" blue light (less than 500 nm), which humans can see, meaning the increases in brightness detected here are even greater with respect to human vision.
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Science Advances