Earth & Conservation

Light Pollution Poses a Growing Threat to Human Health and Biodiversity

Economic growth in the developing world is boosting livelihoods, but it is also disturbing plant and animal life that evolved with a daily cycle of light and darkness.

Nighttime on Earth is getting brighter.
 
The rise of developing economies in Africa, Latin America, and Asia isn’t just raising global greenhouse gases emissions and making the planet warmer. It’s also spreading nighttime light to regions of the planet that didn’t have it before, parting the global curtain of night.
 
“We’re losing more and more of the night on a planetary scale,” Kip Hodges, professor of earth and space exploration at Arizona State University and deputy editor of the journal Science Advances, told Seeker.
 
The impact won’t just be felt by poets and stargazers.
 
The dangers, Hodges said, include the “well-established negative effects of light pollution on human health, ecosystems, and astronomical research.”
 
According to a new paper published in Science Advances, the artificially lit surface of Earth at night increased in radiance and extent by about 2 per cent annually from 2012 to 2016. To make that measurement, Hodges and his team used first-ever calibrated satellite radiometer designed especially for nighttime lights. A radiometer is any device that measures electromagnetic radiation.
 
An influx of new light can wreak havoc on natural systems that have evolved to live partly in darkness, the authors said.
 
A big example: nocturnal animals, including some 30 percent of vertebrates and 60 percent of invertebrates.
 
Indeed, changing night patterns threaten biodiversity, migration, and reproduction habits for a wide range of animals from insects to fish and birds and have an impact on plants and microorganisms, too.
 
“From an evolutionary perspective now, artificial light at night is a very new stressor,” said Franz Holker, one of the paper’s authors. “The problem is that light has been introduced in places, times and intensities at which it does not naturally occur and many organisms, there is no chance to adapt.”
 
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To be sure, the increase isn’t uniform around the world.
 
The authors said the change observed in their study varied greatly by country, with some places far exceeding the overall global rate.
 
Some countries, such as war-torn Yemen and Syria, became darker over the course of the study period.
 
Some of the world’s brightest nations, like the United States and Spain, remained relatively stable. But most countries in South America, Africa, and Asia became increasingly radiant.
 
Globally, the increase in light emission appears to correspond closely to the rise in overall economic activity.
 
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For their study, the scientists used a satellite radiometer designed especially for nighttime lights known as a Visible/Infrared Imager Radiometer Suite, or VIIRS.
 
Notably, the authors point out, VIIRS only detects light emitted between 500 and 900 nanometer wavelengths. It does not “see” blue light (less than 500 nanometers), which humans can see, meaning the increases in brightness detected are even greater with respect to human vision.
 
“Natural light cycles have been fundamentally disrupted by the introduction of artificial light into the nighttime environment,” Holker said. “We are convinced that artificial light is an environmental pollutant with ecological and evolutionary implications for many organisms from bacteria to mammals, including us humans and may reshape entire social ecological systems.”

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