Three hundred years after artificial lighting first illuminated our cities, we have so much light it creates public health and ecological troubles. The new world atlas of light pollution study found that over 99 percent of US and European citizens and 80 percent of the world live under artificially bright skies. Over one-third of all humans can’t see the Milky Way.
Biodiversity and ecosystem process are thrown out of synch due to never-night lights. Migrating and nocturnal birds are confused and often killed by city lights. For example, in Hawaii, shearwater fledgling birds mistake the bright floodlights at high school football stadiums for the moon, and fly in circles at the stadiums. Exhausted, the birds fall out of the sky and are easy prey for cats or are hit by vehicles. Bats and other wildlife also are disturbed by lights. Plants are leafing out earlier in spring, tricked by artificial night lighting across entire regions.
The Daily Bucket, a regular feature of the Backyard Science group, is a place to note any observations of the world around you. Animals, weather, meteorites, climate, soil, plants, waters are all interesting. What is going on around you? Each note is a record that we can refer to in the future as we try to understand the patterns that are quietly unwinding around us.
One study looked at 13 years of spring bud burst in the U.K. for four deciduous tree species and found it occurs 7.5 days earlier. The later a tree species normally begins to open leaf buds, the more intense the effects of artificial lights. This is separate from changes due to urban heat sinks and global warming (although these factors also affect plants), the study controlled for those triggers and focused solely on the effects of artificial lighting. This was one of the first studies to look specifically at how larger scale light pollution affects plants.
Skyglow, diffuse light scattered in the atmosphere from city lights, can illuminate areas of many square kilometres to levels exceeding moonlight, but effects of artificial light on phenology have to date only been recorded as a consequence of direct illumination in the vicinity of light sources, which can be several orders of magnitude brighter.
Global warming, too, is changing plant phenology and by the end of this century spring may arrive 23 days earlier. When plants are tricked into leafing out earlier and then the weather isn’t supportive of continued growth, the cold will damage and kill some plants. Agriculture depends on regular growth patterns and coordination with other plants and animals, many of whom come from areas with more artificial lighting than rural crop fields.
Average day of year for spring onset defined by leaf out (LEFT) and first bloom date (RIGHT)
Earlier spring might seem like a bonus to winter-weary humans, but plants and animals synchronize with each other and if plant phenology changes but that of animals doesn’t, both are in big trouble. Plants offer shelter, food, and safety to wildlife and, in turn plants may depend on the animals for pollination and seed dispersal. But wildlife and plants often are responding to different sets of environmental triggers.
For example, long-distance migratory birds respond to cues present in their overwintering habitat, such as day length, while plants in their summer breeding grounds respond to local environmental cues like temperature. Birds that have adapted to migrate earlier have maintained their population levels, while birds that retained historical temporal patterns in migrations have declined, at least in part due to phenological mismatches with plant-based resources…. Increasing temperatures have led to poor synchronization between moth emergence and leaf out of host trees.... Ultimately, the ability of a species to respond to rapid phenological changes will depend upon generation time, levels of genetic variability, and the plasticity of phenological and behavioral traits….
The scientists who studied spring plant phenology recognize that detailed locale- and species-specific studies are needed “to better understand the potential effects on natural and agricultural systems.” They have created an online weather data base that includes data from their study in support of such fine-grained research.
While reversing the tide of climate change may not be available right now, light pollution is understood and can be addressed. (I added the bullet format below.)
The main prescriptions to lower light pollution are as follows:
- full shielding of lights (that is, do not allow luminaires to directly send any light at and above the horizon or outside the area to be lit),
- using the minimum light for the task, shutting off light or lowering its levels substantially when the area is not in use,
- decreasing the total installed flux (as is happening to most other pollutants), and
- strongly limiting the “blue” light that interferes with circadian rhythms and scotopic vision.
Technology may help to further reduce the impact of light pollution with the implementation of adaptive lighting (for example, street lighting that is governed by real-time sensors of traffic and meteorological conditions, substantially reducing the light during most of the night, in periods of low or no traffic).
Chicago is reducing city lights at night twice a year during bird migration when an estimated five million birds (250 species) move through the city. And there are signs this works well.
One night “[t]here was a tragic mix up and the lights did not go out on schedule. We had a heavy night of migration and there were birds everywhere with few survivors. The next night, the lights were out and the drop in fatalities and injuries was amazing—we guess at an 80 percent drop. We could still hear the birds flying, but they made it safely over the buildings that night.”
New York City in the Atlantic flyway also turns down the lights to protect migrating birds. So are other cities like Baltimore, Washington DC, Minneapolis, and San Francisco.
...many migrating species - including colorful warblers and other song birds - fly at night and navigate by the stars, using constellations to guide them.
But outdoor nighttime lights, especially in bad weather, can disorient the birds and cause them to crash into windows, walls, floodlights or the ground.
The phenomenon, called "fatal light attraction," has killed an estimated 500 million to one billion birds annually in the United States, the governor's office said, citing U.S. Department of Agriculture data.
you too can help mitigate light pollution impacts. Here’s a one minute lesson.
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