Feature

Degraded Darkness

IT’S TEMPTING TO ASSUME that artificial light distresses only a few exquisitely sensitive species. But mounting evidence suggests that disappearing darkness undermines our best conservation efforts.

On a pair of sweltering days one recent July, Sharon Wise and herhusband Bryant Buchanan rigged strands of white Christmas lights from treeto tree in the wilderness of Virginia. No nativity scenewas in evidence, no plastic reindeer, and certainly no snow. Any neighborsthe couple might have impressed with their early display of yuletide spiritwere in distant Utica, New York, where both biologistslive and teach.

Butthe redback salamanders (Plethodon cinereus)that hide all day beneath the leaf litter of Mountain Lake Biological Stationcertainly took note of the couple’s efforts. When the researchers and threeof their students switched on the lights at sunset one evening, the nocturnalsalamanders responded with the amphibian equivalent of pulling the coversover their heads. They waited an hour longer than usual to get up for breakfast.

Thatdelay concerns Wise. Under normal conditions, she knows, the salamandersemerge soon after nightfall and forage for just a few hours. But artificialillumination from buildings, road lights, and distant urban glow increasinglybathes organisms that, like Mountain Lake’s redbacks,have adapted to live in the dark.

Doesa later start for the salamanders mean fewer nightly meals and fewer calories?Does that cut into their fertility or increase their mortality? What doesit mean for the insects that the salamanders eat and for the predatorsthat, in turn, eat them? Wise doesn’t yet have answers. Nor do other researchersstudying the incipient field of artificial light ecology have a full graspon parallel questions about a broad range of organisms and ecosystems.

Nevertheless,as these scientists begin to assemble an understanding of the ecologicalconsequences of artificial light, they are recognizing numerous impacts.A few examples—sea turtles, for instance, and migratory birds—may be familiar.Most are not.

Manyof the effects of artificial light may resonate up and down food chains,dragging whole ecosystems into imbalance. And by modifying the playingfield on which nocturnal organisms develop, interact, and reproduce, artificiallight may sculpt not only their individual lives but also the biologicalevolution of their species. That, says Buchanan, “isthe most overlooked of all of the potential ramifications of artificiallight.”

Asscientists grapple with artificial light’s effects, forward-thinking conservationists—anda handful of sympathetic developers and regulators—are working to integratethe infant discipline into their efforts to mitigate light’s unnaturalecological impacts.

Naturaldarkness, once a given, has become an ecological resource of shrinkingabundance. Everyone who has squinted into a street lamp or stared at lightsvisible through a window has experienced glare—light that strikes the eyedirectly rather than hitting the object it’s intended to illuminate. Thosewho have also seen composite nighttime satellite photos of Earth recognizehow effective humans have become at dispelling the dark. Thickly populated,industrialized regions of the globe appear so starkly illuminated in theseimages that it’s easy, for example, to discern the intricate outlines ofthe Great Lakes. Italian astronomer Pierantonio Cinzano has compiled the first world atlas of night sky brightnesswith satellite data and models of light propagation. It reveals that one-tenthof the world population, approximately 40 percent of the U.S. population, andone-sixth of the European Union population live where nighttime brightnessis too intense for the human eye to use night vision.

Notall light that goes up comes down, but a considerable amount of it does.Reflected off moisture and dust in the atmosphere, it creates a nighttimetwilight known as sky glow. “I’ve been amazed at how far light will travel,” saysChad Moore, a physical scientist with the National Park Service. Majorcities can broadcast sky glow as far as 250 to 300 kilometers, perpetuallyilluminating a sector of the sky everywhere within that radius. “We’vediscovered a pollutant,” Moore says, “andwe’ve saturated our environment with it.” When distant glow falls almosthorizontally on hilly terrain, slopes that face the city can be bathedin light, whereas less-exposed hillsides retain nearly natural levels ofdarkness. That effectively fragments the habitat into areas that are moreor less suitable for nocturnal species, depending solely on their orientationto the sky.

Basedat Bryce Canyon National Park in Utah, Moore hasset out to inventory the night sky in as many U.S. nationalparks as possible and to establish baseline data that the government canuse to monitor artificial light, just as it tracks other pollutants. Usinga research-grade digital camera and a wide-angle lens, Moore and his colleaguestake 360-degree snapshots of the night sky from vantage points within thenation’s natural treasures. So far, his team has surveyed about 20 nationalparks and monuments. At many of the sites, artificial illumination is comparableto at least the brightness of a crescent moon. That modest glow might notsound like much of a problem, but consider how little light it takes toproduce biological effects. One lux, a unit of illumination, corresponds roughly to dim interiorlight or the halo of a street lamp. An unobscured fullmoon provides about 0.3 lux. In light measuringless than about 0.01 lux, says Utica College’sBuchanan, “you can see objects, but you would have trouble writing. Youmight not be able to tell the difference between an M&M and a deerpellet.” Squirrel tree frogs (Hyla squirella),by contrast, can see well enough to navigate and forage at 0.0001 lux orless, and they avoid activity when illumination exceeds 0.001 lux.Other frog species favor even darker conditions.

It’stempting to assume that artificial light distresses only a few exquisitelysensitive species. But mounting evidence suggests that the disappearanceof darkness can affect plants and animals in a variety of ecosystems. Snakepopulations are declining in the vicinity of developing parts of California,for example. And intriguingly, it seems that not all the blame lies withfamiliar culprits like new roads and neighborhoods. Nocturnal snake speciesare thinning out more rapidly than diurnal snake species, even in areaswhere development isn’t cutting directly into snake habitat. “There arecertain areas in southern California,” saysbiologist Robert Fisher of the U.S. Geological Survey, “that have whatseems like suitable habitat for these nocturnal snakes. But they’re notthere, even though their diurnal counterparts are.”

A few pioneering scientists have started down the longroad toward understanding light pollution’s ecosystem-scale ramifications.Late on a summer’s night, you might spot Marianne Moore (no relation to Chad of the NationalPark Service) adrift in a rowboat on Boston’s Jamaica Pond.Hours after the sun’s last rays have faded, the Wellesley College limnologist andtwo of her colleagues put in and row out to the pond’s middle. Whileone researcher holds a light sensor aloft, another toils beneath a blackshroud to keep the glow of a laptop screen from fouling their data collection.

“Somebodytold us we look like we’re transporting illegal aliens,” chuckles Moore.She and her team have occasionally had to placate suspicious police officersor explain themselves to locals who jog on the lighted paths ringing theshore. In truth, the cruises are part of their study of how much nocturnallight penetrates the water’s surface at several lakes in NewEngland.

Moore suspectsthat artificial illumination alters aquatic ecosystems from the smallestorganisms on up. The implications are far reaching and could ultimatelylink light pollution to water quality. Minute zooplanktonlurk well below the surface during the day to avoid predators, thenrise to graze on algae at night. But artificial light discourages themfrom venturing toward the surface. “If their grazing is inhibited . . .effects will cascade up the food chain,” Moore says.Algae populations could explode in response to reduced predation, and thoseblooms would deplete dissolved oxygen critical to fish, crowd out other photosyn-thesizers,and cast unwanted daytime shade on submerged aquatic vegetation that provideshabitat for juvenile fish.

WhenMoore and her colleagues experimentally blocked light from filtering intothe depths, they found that some small taxa of zooplankton ascended twoto three meters more than the organisms did under typical unnaturally brightconditions. Moore expectseven stronger effects among larger kinds of zooplankton, some of whichare known to avoid levels of illumination comparable to bright starlight.The intensity of artificial light shining on Jamaica Pond is considerablybrighter than starlight, she has found, even on cloudless nights. Whenclouds roll in and reflect Boston’sglow downward onto the pond, light intensity can triple to almost two-thirdsthe luminosity of the full moon.

Moore hasan idea for testing whether light pollution has steered evolution in JamaicaPond during the century that it has been bathed in artificial light atnight. Certain zooplankton lay eggs that settle to the bottom and can remainviable in a suspended state for decades, creating an “egg bank” that storesin the sediments the genetic traits of successive generations. Moore envisions digging up eggs, determining when they were laidbased on the age of adjacent sediment, hatching them, and then exposingthe organisms to light to see whether their responses vary according totheir age.

“Invertebratesevolve very quickly, so it’s very reasonable to expect that they’ve respondedto a history of artificial light,” Moore says.By contrast, longer-lived organisms such as fish probably need more timeto adapt. That inequality could add to stress on fish populations, shesays.

Ifthe science relating to light pollution’s ecological impacts remains inits infancy, regulation to minimize its effects in sensitive areas hasbarely been conceived, says Sara Wan of the California Coastal Commission.

Nevertheless,perceived ecological threats from light pollution have helped stop a smatteringof incautious development initiatives. In 1999 the commission rejectedan application to add dazzling ornamental floodlighting on the Vincent Thomas Bridge in Los Angeles afterhearing ecologists’ objections. One of the gravest concerns was that powerfulbeams of light would disorient and fatally attract migratory birds, saysCatherine Rich, a cofounder of The Urban Wildlands Group who presented to the commission scientificdata against the project. The data did not make an absolutely airtightcase, but they raised substantial cause for concern, says Wan, who holdsadvanced degrees in both biology and electrical engineering. Developerssubsequently modified the proposed lighting design to reduce the lightemissions. The final plan is ecologically so much more sound than the originalproposal, Rich says, that her conservation think tank endorses it.

In Bangor, Maine,environmental activists successfully challenged a proposal to build a Wal-Mart Supercenter.In March 2003, the state’s Board of Environmental Protection ruled thatdevelopment of the site, including lights shining over the parking lot,would pose unacceptable risks to neighboring wetlands. In Seattle,critics of a proposal to construct lighted sports fields at Sand Point Magnuson Park havemade the impacts on wildlife and the night sky central to their opposition.Light pollution from the fields would shine onto adjacent wetlands and lakeshore.

Mostregulators, however, rarely hear conservationists object to developmentproposals on the basis of light pollution, Wan believes. Scientists andconservationists may not feel tempted to appear at public hearings withoutrock-solid cases, she says, but their frequent silence means some regulatorsremain wholly unaware of the issue.

On another front, Michael Mesure of the Toronto-based nonprofit, Fatal Light AwarenessProgram, has been leading a campaign against light pollution in Toronto since 1996. Thefirst time Mesure witnessed the aftermath ofthe phenomenon known as “tower kill,” he could hardly believe his eyes. Even before he climbedout of his car, he could see in downtown Toronto’s pre-dawn glooma bird carcass on the sidewalk. Others lay nearby. The migrating animalshad been lured off course by lights on high-rise office buildings and hadfatally collided with the structures.

Onsome mornings since that day in 1988, Mesure and an army of volunteers have identified more than 1,000 birds that had perished in this way during the previousnight. The Fatal Light Awareness Program targets tenants in downtown Toronto’shigh-rises, and it advocates the use of window shades or blinds and directedtask lighting at workstations, as well as switching off lights in unusedareas at night. Over the past five years, a 17-percent reduction in theamount of light escaping from those buildings has noticeably reduced thevolume of nocturnal tower kill, Mesure says.

Evenwhere steps have been taken to mitigate light pollution, organisms facethe threat of ever-bigger, ever-brighter civilization. At the loggerheadturtle nesting grounds in Florida,says turtle researcher Michael Salmon of Florida Atlantic University, “theproblem is fast becoming not the amount of light at the beach but rathersky glow from inland.” Salmon argues that the growing threat to darknessmust be attacked at its source—population centers. “Nothing covers that,” hesays, “except having a national policy that governs how lighting is usedeverywhere.”

Thatidea might sound more farfetched than it is. The Czech Republic’sparliament set an international precedent in 2002 when it passed the firstnational law to address light pollution, which requires shielding of publiclights among other measures. At least 11 U.S. statesand numerous towns and counties have also enacted laws or ordinances thatregulate at least some aspects of light pollution.

That sort of sky change would be welcome elsewhere. In upstate New York,Bryant Buchanan is gathering data on nocturnal illumination in one of hisfavorite scientific stomping grounds, Utica Marsh. Near a brightly lit roadwaythat cuts through the wetland, he pauses and holds up a sensor to measurelight from each of the cardinal directions. Then, in the columns and rowsof his field notebook, he records the data. Even without a flashlight, hehas no trouble writing.

Ben Harder covers the environment for Science News and has written in printor online for National Geographic, Science, and U.S. News & World Report.

For More Information

Miscellaneous papers on the ecologicalconsequences of artificial night lighting can be downloaded from www.urbanwildlands.org

Pierantonio Cinzano’s mapsof night sky bright-ness can be seen at dipastro.pd.astro.it/cinzano