Darkness is disappearing from Earth, and that is a bad thing.
More than 80 percent of the world and more than 99 percent of the U.S. and European populations live under nighttime skies that glow with unnatural light, according to a study released last Friday.
Artificial light from buildings, streetlights, and other human sources prevents more than one-third of the world's people from seeing our Milky Way galaxy at night, including 60 percent of Europeans and close to a staggering 80 percent of North Americans.
"Light pollution needs to be addressed immediately because, even though it can be instantly mitigated (by turning off lights)," the authors write in the study, "its consequences cannot (for example, loss of biodiversity and culture)."
A group of researchers drew up an "atlas of light pollution" using images from NASA's Suomi NPP satellite, and published their research in the journal Science Advances. The map gives a clear, and startling picture of how much of the Earth cannot see the stars.
But can light really "pollute?" Why does having darkness at night matter?
Recent research has suggested the disruption of natural darkness has been bad for all sorts of living things, affecting coral reefs and other marine life, bird migrations, and plant life (as well as food for plant-eating animals.)
But bright night skies can also be bad for human health and well-being.
The science examining the effect of glowing skies on health is understudied, said study author Christopher Kyba. But some research suggests light has the capacity to disrupt sleep by disturbing the circadian rhythms that determine when we feel tired and when we feel wakeful.
Disrupted circadian rhythms have been connected to depression, insomnia, cardiovascular disease, and even cancer, according to comments from Paolo Sassone-Corsi, chairman of the Pharmacology Department at the University of California, Irvine in a 2009 paper on light pollution in Environmental Health Perspectives. "Studies show that the circadian cycle controls from ten to fifteen percent of our genes," he said. "So the disruption of the circadian cycle can cause a lot of health problems."
And unless you have blackout curtains, it is likely that at least some light is filtering through the window at night.
It can even mess with scientific research, and local economies. Astronomers say that it makes it harder to study the skies, and visitors to tourist destinations, such as the National Parks, say they do not see as many stars at night as they would like.
So what to do about it? For one thing, some have advocated reducing unnecessary light. This would include shutting lights off in unoccupied buildings, for example.
Other solutions might be a bit harder to implement. Some crime prevention advocates maintain that more streetlighting reduces crime and makes people feel safer, while some dark sky advocates question the connection between bright lights and safer streets. Some criminologists point out the seemingly obvious, but easily missed point that streetlights help criminals see as much as they do victims.
A possible compromise could involve installing motion detectors on streetlights, which are already in use in some places. The authors also observe that driverless cars, a much vaunted technology of the future, would not require streetlights.
Cities such as Flagstaff, Arizona, have already implemented light-reducing measures. Flagstaff took the measure in part to preserve the dark sky for a nearby astronomical observatory, and a local community of astronomers. The city of nearly 70,000 people thus became the world's first "International Dark-Sky City" in 2001.
The city of Ketchum, Idaho, has ordinances in place that require lights to be "shielded" so the light points down toward the street. Rather than reducing the number of lights, the shields simply direct the light away from the sky, improving the darkness.
Indiana, Texas, Illinois, and California, are also home "Dark-Sky" cities, and the study says that larger regions in Chile, Italy, and Slovenia, have successfully introduced dark sky programs on a large scale.
The researchers also call for "strongly" limiting the so-called blue light that has become common in recent years in LED's, electronic devices, and certain high-efficiency bulbs. Studies have shown that this light is disruptive to circadian rhythms that govern sleep cycles.