The Vanishing Night: Light Pollution Threatens Ecosystems
The loss of darkness can harm individual organisms and perturb interspecies interactions, potentially causing lasting damage to life on our planet.
As darkness fell over Manhattan on the ninth anniversary of the September 11 attack, two beams were shot into the sky at the site where the Twin Towers once stood. The commemorative lights had appeared annually since the towers fell, but in 2010 onlookers noticed something unusual: countless white sparkles glittering within the white beams.
The mysterious white objects turned out to be thousands of migrating birds. Although the public had just taken notice of this spectacle, conservationists had been aware of the phenomenon for several years. Shortly after the tribute first appeared, New York City Audubon, a conservation group, helped initiate a program to monitor the installation and temporarily shut off the lights whenever too many birds got caught in the beams. In a later analysis of the bird populations on memorial nights between 2008 and 2016, researchers found that, although the short-term shutdowns were effective, approximately 1 million animals had been attracted to the glowing memorial and had become distracted from their normal migratory routes.1
This annual demonstration of how artificial illumination can influence animal behavior is but one instance of a much bigger prob- lem. Around 80 percent of all humans—and more than 99 percent of people in the US and Europe—now live under light-polluted skies. In addition to direct lighting from urban infrastructure, light reflected from clouds and aerosols, known as skyglow, is brightening nights even in unlit habitats. As electric lights become more energy- and cost-efficient, the proportion of lit surfaces keeps rising. Meanwhile, the list of organisms that researchers document to be affected by Earth’s unnatural glow is growing right along with it.
