Light pollution is getting exponentially worse. The area of Earth lit by artificial lights grew by 9 per cent in four years. If that continues, the total illuminated area of the Earth will double from what it was in 2012 before 2050.
The retreat is likely to impact nocturnal wildlife and people’s health, by disrupting natural day-night cycles, as well as further obscuring our view of the heavens.
“Dark areas are being lost in places where nocturnal animals, insects and plants have adapted to darkness over billions of years,” says of the Leibniz Institute for Freshwater Ecology and Inland Fisheries in Berlin, Germany. “Our most dramatic result is the exponential growth in illuminated areas and light levels globally.”
Advertisement
±áö±ô°ě±đ°ů, of the German Research Centre for Geosciences in Potsdam and their colleagues used data from a satellite that senses light with wavelengths between 500 and 900 nanometres – from green light to infrared. The satellite could resolve surface features as small as 750 metres, allowing precision monitoring of artificial lighting in towns and cities.
Lights everywhere
From 2012 to 2016, the area illuminated and global brightness both rose by 2.2 per cent per year. If that continues, “the Earth’s lit area could double in 32 years from 2012,” says Kyba.
The brightening was most dramatic in rapidly industrialising countries in South America, Africa and Asia. “South Sudan was the fastest, with an increase in lit area from 52 to 403 square kilometres, an increase of 67 per cent per year,” says Kyba. Lighting also spread fast in Ghana and Vietnam, by 19 and 15 per cent per year respectively.
Light pollution remained more static in some heavily-lit rich countries, including the USA and Spain. It only decreased in war zones like Syria and Yemen, due to the destruction of buildings and infrastructure.
“We have known that artificial light at night is a globally widespread pollutant for some time, but estimating the rate at which it is expanding has been technically challenging,” says at the University of Exeter, UK. “This paper overcomes many of these technical issues, providing reliable estimates of the global rate of expansion in artificial light pollution. The numbers are truly shocking, given that we know that illuminating the nocturnal environment can have widespread ramifications for ecology and human health.”
Cheap light bulbs
Among the culprits are energy-efficient LED lights, which were brought in to cut electricity use and greenhouse gas emissions. While they’re twice as energy-efficient as the older lighting they replace, they’re also much cheaper. As a result, they’re making installation of new lighting affordable, even where it’s not strictly needed.
The widespread use of LEDs in cities is also creating a phenomenon called “skyglow”, in which the harsher blue wavelengths are reflected back down from the sky to create a city-wide aura. “It produces these light domes above cities,” says Hölker.
However, Hölker says LED lighting can help retain or expand dark areas if used intelligently. He points out that Germans emit three to five times less light per head than Americans, despite roughly equal wealth levels.
Artificial lighting is known to be harmful to many species. Moths and other insects are known to perish in large numbers because they are attracted to street lights, and this has had knock-on effects on pollination, decreasing seed yields in some plants by as much as 30 per cent. Animals such as bats and frogs are adversely impacted too, says Hölker.
“Central to minimising the ecological impacts of increasing use of light will be controlling where we direct it,” says of Bard College in New York. “So much of the light we produce is unintentionally directed towards light-sensitive species and ecosystems, or straight up where it reflects back to Earth from clouds.”
Science Advances
