LIGHT pollution is now so bad that a dull orange 鈥渟kyglow鈥� obscures the stars in more than two-thirds of the world鈥檚 crucial habitats. And we have almost no idea how this affects wildlife.
There are two kinds of light pollution. The first is the intense brightness close to artificial lights like street lights, which often means night-time cities are lit up like Christmas trees, and we know a lot about its effects on nature.
But further from cities, although there is less bright light, there is still a diffuse orange glow in the sky. This skyglow is widespread: about a third of people cannot see the Milky Way at night because of it.
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Jo Garrett at the University of Exeter, UK, and her colleagues have now mapped how far skyglow has penetrated into havens for threatened wildlife known as Key Biodiversity Areas. They took existing satellite data on the global spread of skyglow and overlaid the locations of these wildlife hotspots.
About half the biodiversity areas had artificially bright skies throughout, and fewer than a third had no light pollution at all. Rates of light pollution were significantly higher in Europe and the Middle East, where a higher proportion of the biodiversity areas experienced skyglow, than in other regions.
Garrett鈥檚 team also found that more of the biodiversity areas were affected in regions that were wealthier and more densely populated (Animal Conservation, ).
This is a warning to emerging economies, says Christopher Kyba at the GFZ German Research Centre for Geosciences in Potsdam. 鈥淭here鈥檚 a problem coming for these places, because they鈥檙e going to develop, and when they do they鈥檙e going to get very bright.鈥�
However, we don鈥檛 know what the effects of spreading skyglow will be. Many studies of light pollution have focused on organisms living in cities and other brightly lit places. They have revealed that illuminated nights change animals鈥� life cycles and when plants flower, and can affect predator-prey relationships. This can be shown by bringing animals into the lab or placing lights in their habitats.
But it is much harder to determine the consequences of skyglow, which is both fainter and more widespread. 鈥淚 think the consensus among the scientific community is that skyglow is probably having very widespread impacts,鈥� says Thomas Davies at Bangor University in the UK. 鈥淏ut we鈥檙e yet to design the type of experiments that are capable of quantifying that.鈥�
Tackling skyglow, and other light pollution, will mean both using less light and being smarter about it when we do use it, says Kyba. Street lights could be turned off in the darkest hours of the night, when most of us are asleep and the risk of accidents or violence is minimal. Limits could also be set on the brightness of illuminated signs and lights on building facades.
The direction of light is also crucial, says Kyba. The main cause of skyglow is light that shines horizontally, aiming just above the horizon. 鈥淲ith street lights, eliminating emissions in that direction can be really effective at reducing the total sky brightness,鈥� he says.
