For the 11th year running, cities worldwide will turn their lights off Saturday to mark Earth Hour in a global call to action on climate change.
But the moment of darkness should also serve as a reminder, activists say, of another problem that gets far less attention: light pollution.
More than 80 per cent of humanity lives under skies saturated with artificial light, scientists recently calculated.
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In the United States and western Europe, that figure goes up to 99 per cent of the population, most of whom cannot discern the Milky Way in the night sky.
The moon rising above the Manhattan skyline in New York. For the eleventh year on March 25, 2017, cities will turn their lights off for Earth Hour. Photo: AFP
Artificial lighting has been shown to disturb the reproductive cycles of some animals and the migration of birds that navigate using the stars, and to disorient night-flying insects.
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For humans, circadian rhythms that regulate hormones and other bodily functions can also be thrown out of whack by too much light at night.
