The future is bright, but we’re losing darkness: threats to human and ecosystem health

World map of artificial sky brightness [5]
This year’s Nobel Prize in Physiology or Medicine was awarded to three scientists who have worked for decades to identify the molecular mechanism controlling our bodies’ internal clocks—our circadian rhythms.

Jeffrey C. Hall, Michael Rosbash, and Michael W. Young first isolated the gene that controls circadian rhythms back in 1984. They discovered that this gene, called period, encoded a protein that accumulated during the night and degraded during the day. They believed that this protein, which they called PER, somehow blocked the period gene during the day. The system turned out to involve several other proteins that were needed to control the accumulation of the PER protein. Over the years, the scientists went on to discover other components– importantly, one that allows light to influence the 24-hour rhythm[1].

To many of us, circadian rhythms seem like a scientific discovery of the last century. What makes this science prize-worthy today?

More studies are telling us that circadian rhythms have huge implications for human health. Our internal clocks regulate important functions in our bodies such as hormone levels, metabolism, growth, behaviour, body temperature, and sleep. Misalignment of our lifestyles and our circadian rhythms increases our risk of various disorders and diseases, including cancer[2][3]. We still don’t know the details of how circadian disruption affects mental health.

It looks like we need darkness—but our world is only getting brighter.

Vincent Van Gogh’s Starry Night (1889) [4]
In 1889, Vincent Van Gogh was staying at an asylum in Saint-Remy in France, where he painted Starry Night. The painting is believed to show the view from his bedroom window. If you were to return the same location today, you would see an entirely different scene: the Milky Way is no longer visible.

The New World Atlas of Artificial Sky Brightness, published in 2016, revealed that artificial light has now changed the view of the night sky for 83% of the world’s population; 99% of U.S. and European populations live under light-polluted skies[5]. Though this change has corresponded with an improvement in quality of life and safety, it’s had some negative side effects.

We have lost the ability to look up and ponder the night sky– a significant cultural loss in itself– and we know that artificial light at night is affecting human health. It comes as no surprise that it is having an effect on the health of the ecosystems around us, but we’re still not quite sure to what extent.

There are several well-known examples of human-introduced light negatively affecting animal behaviour; perhaps the most commonly cited is the disorientation of hatching sea turtles[6]. Hatchlings have evolved to move away from low, dark silhouettes of dune vegetation and towards the lighter horizon where the sea reflects the stars. Beachfront lighting has eliminated these historic light patterns and caused hatchings to become disoriented, running away from safety and towards roads and predators.

An unfortunate fate also awaits birds whose migratory paths intersect heavily lighted areas. They are particularly susceptible to artificial light because of their adaptations for navigating and orienting in darkness[7]. Large numbers of nocturnally migrating birds can be affected when inclement weather forces them to fly lower than they normally would. Once in heavily lighted areas, birds may collide with tall lighted structures, or become exhausted as they are unable to escape.

As an example, at the annual 9/11 Tribute in Lights in New York City, two beams from 7,000-watt bulbs shine four miles into the sky and can be seen from 60 miles away. Birds get trapped in the bright lights, and volunteers stand by to help. Once there are 1,000 trapped birds—or once a bird falls to the ground from exhaustion—the lights are turned off for 20 minutes, allowing the birds to escape. Similarly, many insects congregate around light sources until they die from exhaustion[8].

In addition to having an effect on individual species behaviour, artificial light affects community dynamics. Having a “perpetual full moon” favours light tolerant species; prey can no longer rely on the cover of darkness. One study found that harbour seals congregated under artificial to eat juvenile salmonoids as they migrated. Removing the light reduced predation levels[6].

There are still gaps in our knowledge; for example, we aren’t entirely sure how light may be affecting species evolution and adaptation[9]. The influence of artificial night at light is only expanding in scope and intensity; studies show that, in many areas, light pollution is increasing at a faster rate than population growth[10]. Our understanding of the ecological consequences of artificial light at night needs to be expanding rapidly, too.

In the meantime, a few helpful organisations are encouraging people to take action and reduce their impact on darkness. Curious readers can check out helpful websites belonging to the International Dark-Sky Association and the Fatal Light Awareness Program. Suggestions range from simply closing our blinds at night to swapping out floodlights for shielded options. As the world is ever-more illuminated, we need to keep asking what changes we can make to reduce the negative impacts of artificial light, both for ourselves and for the ecosystems around us.


[1] Rosbash, M., Davidson, N. and Sinsheimer, R. (2017) ‘A 50-Year Personal Journey : Location , Gene Expression , and Circadian Rhythms’. Cold Spring Harbor perspectives in biology [electronic resource] doi: 10.1101/cshperspect.a032516

[2] Navara, K. J. and Nelson, R. J. (2007) ‘The dark side of light at night: Physiological, epidemiological, and ecological consequences’, Journal of Pineal Research, 43(3), pp. 215–224. doi: 10.1111/j.1600-079X.2007.00473.x.

[3] Falchi, F. et al. (2011) ‘Limiting the impact of light pollution on human health, environment and stellar visibility’, Journal of Environmental Management. Elsevier Ltd, 92(10), pp. 2714–2722. doi: 10.1016/j.jenvman.2011.06.029.

[4] Van Gogh, V. (1889) The Starry Night [painting]. Available from: [Accessed 30 October 2017].

[5] Falchi, F. et al. (2016) ‘The new world atlas of artificial night sky brightness’, Science Advances, 2(6), pp. e1600377–e1600377. doi: 10.1126/sciadv.1600377.

[6] Longcore, T. and Rich, C. (2004), Ecological light pollution. Frontiers in Ecology and the Environment, 2: 191–198. doi: 10.1890/1540-9295(2004)002[0191:ELP]2.0.CO;2

[7] Van Doren, B.M., Horton, K.G., Dokter, A.M., Klinck, H., Elbin, S.B. and Farnsworth, A., 2017. High-intensity urban light installation dramatically alters nocturnal bird migration. Proceedings of the National Academy of Sciences, 114(42), pp.11175-11180.

[8] Hölker, F. et al. (2010) ‘Light pollution as a biodiversity threat’, Trends in Ecology and Evolution, 25(12), pp. 681–682. doi: 10.1016/j.tree.2010.09.007.

[9] Swaddle, J. P. et al. (2015) ‘A framework to assess evolutionary responses to anthropogenic light and sound’, Trends in Ecology and Evolution. Elsevier Ltd, 30(9), pp. 550–560. doi: 10.1016/j.tree.2015.06.009

[10] Cinzano, P., Elvidge C. (2003). Night sky brightness at sites from satellite data. Mem. Soc. Astron. It., 74, 456-457

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