Earth Is Too Bright for Its Own Good
The zoologist Johan Eklöf began to consider the disappearance of darkness in our brightly lit world in 2015, when he was out counting bats in southern Sweden. The surrounding grounds were dark, as they had been decades earlier when his academic adviser had tallied the bat populations in the region’s churches.
In the intervening years, however, those churches had been illuminated with floodlights. “I started to think, how do the bats actually react to this?” Dr. Eklöf said.
The short answer: Not well. With his adviser, Jens Rydell, Dr. Eklöf launched a new bat census and discovered that in 30 years — the average bat’s life span — fully half the area’s colonies had disappeared.
That research soon led Dr. Eklöf to investigate how other species are affected by artificial lighting — including the species responsible for installing floodlights in churchyards. The resulting book, “The Darkness Manifesto,” published in Swedish in 2020 and in English last month, is a wide-ranging exploration of humanity’s troubled relationship with darkness, and the damaging effects of our drive to overcome it.
Astronomers first began using the term “light pollution” in the 1960s, and today it most often refers to the persistent glow that emanates from cities after dusk, blocking out the stars and tinting the night sky an orange-gray. By 2016, a full 80 percent of the global population — and 99 percent of the population in the United States and Europe — lived under light-polluted skies.
Earlier this year, a study published in the journal Science found that between 2011 and 2022, light pollution on Earth increased 9.6 percent annually. “It really shook my faith,” Christopher Kyba, a researcher at the German Research Center for Geosciences and lead author of the study, said of the results. “I had been quite an optimist that with newer technology, things were going to get better, because lights are better designed. But instead, what we saw is that most countries are getting brighter.”
Today, one-third of the world’s people cannot see the Milky Way, on even the clearest night. But the impact of all that light goes beyond impeded stargazing. As “The Darkness Manifesto” explains in detail, all living organisms are governed by light-sensitive circadian rhythms that, if disrupted, can unleash effects that range from an impaired sense of direction (pity the poor dung beetle, who, unable to see the stars that help it navigate, cannot get its nutrient-rich ball of excrement home) to mass executions (witness the fate of the swarm of grasshoppers that, drawn by the beam shooting from the Luxor casino, descended on Las Vegas in 2019, only to end up like so much lifeless confetti cluttering the Strip).
But it is not just insects. Newly hatched sea turtles head inland toward the city’s glow rather than to the moonlit sea. Tricked by outdoor lighting, urban trees stay green longer than their rural counterparts. On one Australian island, the light was so disruptive that wallabies, whose gestation is normally triggered by the summer solstice, ended up giving birth so much later in the season that food had run out. Even coral, which in Australia normally reproduces once a year when December’s full moon induces it to release a “snowstorm” of male and female sex cells, is getting confused; disoriented by artificial light, the gamete release is no longer synchronized, diminishing reproduction and contributing, it is thought, to coral bleaching.
Dr. Eklöf also found that light pollution has increased insomnia, depression and even obesity in humans.
Some places are taking action. France has adopted a national policy that imposes curfews on outdoor lighting. And some countries are embracing “dark sky tourism,” which encompasses activities like stargazing walks or excursions to see the Northern Lights.
Dr. Eklöf hopes his book will inspire readers everywhere to embrace the dark more fully.
“Losing the connection to the night sky and to the stars is losing our connection to nature,” he said.