Earth’s nights are brighter

The night outside your window is not just a little brighter than it used to be. Satellite records show Earth’s artificial nighttime light rose by about 16% from 2014 to 2022, even after dimming in some places canceled out part of the increase elsewhere. (nature.com) (reuters.com) Scientists measured this with daily images from the Visible Infrared Imaging Radiometer Suite, a NASA and National Oceanic and Atmospheric Administration instrument that flies over the same places night after night around 1:30 a.m. local time. That lets researchers track streetlights, buildings, roads, fishing fleets, and blackouts the way a heart monitor tracks pulses. (nasa.gov) (lighttrends.lightpollutionmap.info) The new paper says the planet is not simply getting brighter in one smooth line. Each changing location went through an average of 6.6 separate shifts over nine years, which means the map of light now flickers with construction booms, economic slowdowns, wars, disasters, and energy-saving policies. (nature.com) Brightening added light equal to 34% of the 2014 global baseline, while dimming removed light equal to 18% of that baseline, leaving the net increase near 16%. The total area with abrupt change reached 2.05 million square kilometers, and gradual change covered another 19.04 million square kilometers. (nature.com) The fastest growth showed up across parts of sub-Saharan Africa and Southeast Asia, where new roads, expanding cities, and rural electrification are pushing light into places that were darker a decade ago. Europe moved in the other direction in many areas, with energy conservation and light-pollution rules cutting emissions after years of overlighting. (reuters.com) (nature.com) In 2022, the United States produced the highest total nighttime luminosity of any country in the dataset, followed by China, India, Canada, and Brazil. That ranking reflects both population and infrastructure, because a continent-spanning highway network and low-density suburbs throw off more light than a compact city does. (reuters.com) This is not only an astronomy story. Artificial light at night changes the light-dark cycle that human sleep depends on, and sleep researchers have warned that brighter nights can suppress melatonin, delay sleep timing, and disturb circadian rhythms that normally sync to daylight and darkness. (news.northwestern.edu) (reuters.com) The same spillover hits animals that navigate, feed, or reproduce by moonlight and darkness. The International Dark-Sky Association says excessive outdoor lighting disrupts birds, insects, turtles, and other species, especially when blue-rich light-emitting diode lamps spread into habitats that evolved around predictable night. (darksky.org) The irony is that newer lighting can make this worse even when it uses less electricity. Light-emitting diode fixtures are cheap to run, so cities and businesses often install more of them, brighter ones, or ones that stay on longer, which can erase part of the energy savings in a rebound effect researchers have been documenting for years. (darksky.org) (nature.com) The picture from orbit is that modern life is extending the workday, the shopping day, and the road network deeper into the night, but not everywhere in the same way. Some governments are learning that warmer bulbs, shields that aim light downward, and earlier shutoff times can dim a city without turning it off. (reuters.com) (darksky.org)