Emerging threat of the 21st century lightscape to global biodiversity

Over the last century the temporal and spatial distribution of light on Earth has been drastically altered by human activity. Despite mounting evidence of detrimental effects of light pollution on organisms and their trophic interactions, the extent to which light pollution threatens biodiversity on a global scale remains unclear. We assessed the spatial extent and magnitude of light encroachment by measuring change in the extent of light using satellite imagery from 1992 to 2012 relative to species richness for terrestrial and freshwater mammals, birds, reptiles, and amphibians. The encroachment of light into previously dark areas was consistently high, often doubling, in areas of high species richness for all four groups. This pattern persisted for nocturnal groups (e.g., bats, owls, and geckos) and species considered vulnerable to extinction. Areas with high species richness and large increases in light extent were clustered within newly industrialized regions where expansion of light is likely to continue unabated unless we act to conserve remaining darkness. Implementing change at a global scale requires global public, and therefore scientific, support. Here, we offer substantial evidence that light extent is increasing where biodiversity is high, representing an emerging threat to global biodiversity requiring immediate attention. Artificial light encroachment into species rich areas of nocturnal taxa Bars indicate quadrats (20 × 20 km) with both an increase in the extent of artificial light between 1992 and 2012 and greater than average species richness for nocturnal taxa: (a) bats, (b) owls, (c) nightjars, (d) geckos, (e) frogs and toads, and (f) salamanders. Bar height (0–400 cells) represents the increase in the number of lit 1 km2 cells (DN > 5.5) within a quadrat. Bar color represents the species richness z‐score for that quadrat. Two color scales represent high (>0–2 SD above the mean) and very high (>2–3 SD above the mean—values ≥3 are all red) species richness.