Darkening' Cities Is as Important for Wildlife as Greening Them

Urban lighting disrupts wildlife and human health alike, but smarter illumination can help restore balance.

- Nick Dunn

For billions of years, life has depended on Earth's rhythm of day and night. DNA codifies body clocks in all animals and plants, which helps their cells act according to this cycle of light and dark.

Humans have disrupted this cycle, though, by producing artificial light at night. A growing body of scientific evidence shows this can have negative effects on many different forms of life.

Essentially, artificial light at night changes the sensory capacities of living things. It can disturb the magnetic orientation of migratory birds and beguile insects, causing them to become easier prey and exhausting them. The same disruption to body clocks we see in wildlife is also linked to health consequences in people.

Apart from some caves, deserts, and deep-sea trenches, most of Earth has been invaded by light pollution to some degree, or is under threat of its encroachment.

In 2001, astronomer Pierantonio Cinzano and his colleagues created the first global atlas of light pollution. It calculated that two-thirds of the world's population lived in areas where nights were at least 10 percent brighter than natural darkness.

The scale of the problem was updated in 2016 when the team renewed its atlas. By that time, 83 percent of people globally were living under a light-polluted sky—and 99 percent in the UK, Europe, and North America.