Do you live in a city or sub-urban area? Somewhere with restaurants and bars open late, illuminated shops windows tempting you inside, taxi cabs dodging between the traffic lights? Somewhere famous for its stunning skyline, one that paints a perfect picture across the night sky?And have you ever looked up at the night sky and seen…nothing? No stars, no constellations, no trace of the Milky Way. It’s odd because you don’t notice that you can’t see the stars, until you go somewhere where you can, somewhere that’s in total darkness.
I got this opportunity when I climbed Mount Kilimanjaro in September 2013. On the final night, we trekked to the summit in darkness. All you could see were the floating lights of people’s head torches, weaving up the mountain like tiny ants. When i looked up at the night sky, I could see hundreds of thousands of stars. I could make out the shapes of constellations I’d only seen in astronomy books. I could see stars across (what felt like) the whole of Africa. I have to say, it was pretty impressive. It was the most beautiful starry night I’d ever seen. In fact, it was the only starry night I’d ever seen. I’d never seen anything like it.
Despite living in the countryside, the night sky in the North of England looked nothing like that on Kilimanjaro. Granted, there are a few more clouds in England, and sticking your head out of the window to see the stars does not have the same effect as climbing a mountain, but the sky is the sky, it shouldn’t look that different.
This is our reality, captured by Rosino
Compared to the reality we cannot see, ‘Darkened Cities‘ was created by the Thierry Cohen
It was actually whilst writing my dissertation, ‘The Effects of Artificial Night Lighting from Coastal Development on Mammals and Reptiles in the Marine Ecosystem’, that I found the answer to our vanishing night sky. That all sounds more complicated than it actually is (trying to sound smart at university), really the answer is quite simple, it’s just that we aren’t aware of it.
When we hear the word ‘pollution’, many of us think of carbon dioxide, fossil fuels and scary statistics about global warming. These pollutants get the most media attention because we can all see and feel their effects. But there is another pollutant that is quietly cloaking our night sky – light pollution. Saying that, I don’t really like the term light pollution because we associate pollution with something destructive but man-made light is almost essential to our way of life. It lights our homes, our streets, it makes us feel safe. So from now on, I’ll call it artificial night light instead (much better!).
Just so we’re all on the same page, artificial night lights are man-made sources of light which affect humans and wildlife. This could be street lighting, commercial lighting or residential lighting – anything which illuminates the environment! If you were standing under a streetlight at night, you would be experiencing direct light. But if you were a bat (stay with me) and you flew over the streetlight, you would be experiencing indirect light, or sky glow. Sky glow occurs when a light sources illuminates the area of sky above it. In towns and cities, sky glow from all the individual sources of light can illuminate the sky for miles around. And there’s the answer! Even though I live in the countryside, the sky glow from nearby towns and from local light sources prevent me from seeing the stars, they mask the night sky. TAH DAH!
But apart from making the night sky a little less beautiful, why does this matter? We don’t need to see the stars to survive. Why is artificial lighting a problem?
Surprisingly, studies have shown that the two-thirds of our global population live in regions polluted by artificial light and this is having serious effects. One-tenth of our population now have degraded night adapted vision. Our sleeping patterns can be disrupted as our natural body clocks want to sleep when it’s dark, but our nights are getting lighter. Artificial light can increase our risks of obesity, depression, diabetes, breast cancer and more. The list goes on.
But the problems don’t only affect us. The real issues occur for the wildlife that need to see the stars to survive. Nocturnal and migratory animals use the stars to navigate, to regulate seasonal behaviour and to find food. Visualising the stars is key for their survival.
Most research has measured the effects of artificial light for land (or terrestrial) animals, simply because any changes in behaviour are easy to see! However, there’s not much research into the effects of lighting in marine environments (imagine trying to measure a whale’s behaviour constantly for days on end, almost impossible!). But artificial light is very high along coastal zones from coastal developments, offshore oil rigs and light houses, and sky glow is created from nearby cities. Approximately 22% of the world’s coastal regions (excluding Antarctica) are polluted by artificial lighting – that’s huge! There must be some effect. So for my dissertation, I decided to take a look and see what I could find.
My dissertation was 10,000 words long, so instead of asking you to read all that (phew!) I’ll just share three key findings:
- Migratory Birds – as if a migration half way across the world isn’t exhausting enough, we accidentally threw in another obstacle (sorry!). Migratory birds are attracted to artificial lights and can’t help flying towards them. They circle the lights for hours, trapped, until exhaustion or death. These birds never complete migration or reach the breeding grounds to reproduce, so this reduces the number of babies born in the next generation. One study showed that an intense beam of light from an airport ceilometer led to the deaths of 1954,50,000 birds! Oil rigs are also a key source of disorientation for migratory birds and cause many deaths from exhausted, collisions into the oil rigs, or disorientating the birds off course.
- Turtles – white light reduces the success of female turtles nesting and of hatchling baby turtles surviving. Female turtles don’t like nesting on illuminated beaches because there is a greater chance of predation. They will either abandon their eggs on the beach, or choose a more unfavourable nesting location, decreasing the likelihood the eggs with hatch. Hatchlings are disorientated by artificial lights, wandering all over the beach before eventually reaching the sea. This extends the period of time they are on the beach, increasing the chances of predation. If the hatchlings do reach the sea, they are exhausted and the likelihood of drowning is increased. These effects have reduced turtle populations worldwide and will reduce the survival of future generations.
- Seals – artificial lights disrupt celestial navigation (navigating using the stars) and feeding on-shore and at sea. If seals can’t see the stars due to sky glow, they can’t navigate during long feeding trips in the open ocean. However, in some rivers, seals have learnt to use artificial lights to improving their feeding performance (the lights illuminate the prey!). This may sounds like a good thing, but if the seals eat too much, it reduces the prey population too far and disrupts the ecosystem.
So we know the problems, but what about the solution? We can’t exactly turn all the lights off.
We could just change the colour of our lights. Birds are attracted to red and white light, but blue and green have no effect – great, we could just use blue lights from here on out! Well, that would work, but mammals are still attracted to blue light. So we can’t have white, red or blue…purple? You can see the problem – different animals are attracted to different colours of light, there isn’t one single colour that suits everyone. And can you imagine walking around in a world of purple light? Nobody would go for that!
But that’s not the only solution. There are loads of ways we can reduce our lighting and reduce the negative impacts on our wildlife. I’ve made another list (I do love lists) of some easy ways to do this:
- Change the colour of lights on oil rigs to help migratory birds – birds are not as attracted to green lights and workers on the rigs can still work safely under this light
- Use low pressure sodium lights (you know the old yellow coloured street lights? Those!) – these lights aren’t visible to as many animals, so there are fewer negative impacts overall
- Modify outdoor lights to reduce waste light – use low mounted fixtures, shields, automatic lighting systems and caps to limit the angle of light emitted to 70 degrees and reduce upward illumination
- Install light barriers – barriers cast shadows on the beaches, making them more attractive for nesting turtles and reducing disorientation in hatchlings
- Reduce light during nesting seasons or migration times – a temporary inconvenience for us but a huge help to our wildlife!
- Talk about it – the more we know, the more we can do to help!
So there you have it – pretty much my whole dissertation summarised in one blog!
I hope it sparked an interest (light pun!) and that you can do a little bit to help solve the problem of artificial light pollution.
Here’s a photo of me and my friend on Mount Kilimanjaro!
The ‘Sciencey’ Bit:
Here are some of the key studies I cited in my dissertation – have a read if you want some more information about their studies and results! Rich and Longcore’s book is a fab read and is the bible of artificial light information!
Cinzano, P., Falchi, F. & Elvidge, C.D., 2001. The first World Atlas of the artificial night sky brightness. Monthly Notices of the Royal Astronomical Society, 328(3), pp.689–707.
Dananay, K.L., 2013. Morphological and Physiological Effects of Ecological Light Pollution on Mammals and Amphibians in Pennsylvania. Wildlife and Fisheries Science.
Poot, H. et al., 2008. Green Light for Nocturnally Migrating Birds. Ecology and Society, 13: 47(2), pp.1–14
Rich, C. & Longcore, T., 2006. Ecological Consequences of Artificial Night Lighting, Washington, DC: Island Press.
Verutes, G.M. et al., 2014. Exploring scenarios of light pollution from coastal development reaching sea turtle nesting beaches near Cabo Pulmo, Mexico. Global Ecology and Conservation, 2, pp.170–180. Available at: http://www.sciencedirect.com/science/article/pii/S2351989414000274 [Accessed October 2, 2015]
Witherington, B.E., 1992. Behavioral Responses of Nesting Sea Turtles to Artificial Lighting. Herpetologica, 48(1), p.31. Available at: http://proxy-remote.galib.uga.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db=edsjls&AN=edsjls.10.2307.3892916&site=eds-live.
Witherington, B.E. & Bjorndal, K.A., 1991. Influences of artificial lighting on the seaward orientation of hatchling loggerhead turtles Caretta caretta. Biological Conservation, 55(2), pp.139–149. Available at: http://www.sciencedirect.com/science/article/pii/000632079190053C [Accessed October 2, 2015].
Witherington, B.E. & Martin, R.E., 2000. Understanding, Assessing, and Resolving Light-Pollution Problems on Sea Turtle Nesting Beaches. Chelonian Conservation and Biology, 2, p.463. Available at: http://proxy-remote.galib.uga.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db=edsbl&AN=RN026514642&site=eds-live.