Today, little of our planet’s land is dark at night. The starry hubs of cities and ports and vein-like outgrowths of the well-lit suburbs cover the surface of the Earth. The planet may be "a pale blue dot," as Carl Sagan has said; but at night, we're bright. Too bright.
Over thousands of years, Earth’s animals have evolved to have circadian rhythms and internal clocks maintained by the daily light/dark cycle that is disrupted today by light pollution.
Humans are not immune. In 2014, the Washington Post reported that iPads, tablets and smartphones disturb sleep.
Sleep disrupted by light—in particular, the white light emitted by our devices—puts us all at greater risk for high blood pressure and diabetes.
Light pollution takes a toll on wildlife as well, especially in coastal areas where human-population growth and development are greatest. City lights cause what scientists call "sky glow”—the haze of light that halos cities that never sleep.
Sky glow and other sources of light pollution are harmful to many animals, and to sea turtles in particular. Unique creatures, sea turtles are one of the few reptiles that live in the sea, and there are only seven species, six of which are listed as threatened or endangered. They are threatened by light pollution because they depend on the dark for reproduction and for the survival of their young.
Six species of sea turtle live in U.S. waters: the leatherback, green, loggerhead, Kemp's ridley, hawksbill and olive ridley. The flatback is found in the Western Pacific.
Florida's beaches are not just destinations for tourists. They’re also nesting sites for the rare loggerhead, hawksbill and green sea turtles. Leatherbacks have their nesting sites in the sands of popular Costa Rican beaches. Tortuguero National Park, a protected area on the country's northeastern Caribbean coast, is the most important nesting site of endangered green turtles in the entire Western Hemisphere.
However, since 1980, the Costa Rican leatherback population has declined over 90 percent. Poaching, habitat destruction and pollution—specifically light pollution—are the causes.
Female sea turtles come ashore at night to lay their eggs, usually on the same beach where they themselves hatched. But they avoid shorelines with bright lights.
Upon hatching, the baby sea turtles haul quickly for the brightest light on the horizon, following it like a beacon. In a world before the Industrial Revolution, this would have always been the moon shining on the surface of the sea.
But today, shoreline lights from commerce or roadways lure hatchlings away from the water. The 3-inch-long babies move single-pointedly, flippering up the beach in the wrong direction, where they are picked off by natural predators like ghost crabs and herons, or domestic animals like dogs and cats.
The best thing for a sea turtle hatchling is to make it to the sea. There, they’re relatively safe from predators. As adults, they can grow, depending on the species, to a length of 7 feet, feasting on jellies, whose burgeoning populations they keep in check. The sea needs sea turtles.
Dark night skies are a natural resource—one that we all too often take for granted. Before you flick the lights on or peer into your iPhone after the sun has set, ask yourself: “What kind of animal am I?” Like the sea turtle, you’re one that needs the night—free from light pollution.
To learn more light pollution and to see tiny sea turtles hatching from their eggs, visit aqua.org/ablueview.