Recognising effects of light pollution

(MainsGS3:Conservation, environmental pollution and degradation, environmental impact assessment.)

Context:

Recently, the district administration of Ladakh designated six hamlets within the Changthang Wildlife Sanctuary a “dark-sky reserve” – an area whose skies were free of light pollution.
The designation meant that the reserve had a responsibility to keep the skies dark, particularly for the astronomical observatories located in the area.

Light pollution:

In a new study, researchers from Germany and the U.S. analysed a global database of what the dimmest star visible from a particular location is; the database had more than 51,000 entries submitted by citizen scientists.
They found that non-natural light had increased the brightness of the artificial glow of the night sky, or skyglow, by 9.2-10% every year between 2011 and 2022.
Specifically, they reported that skyglow had brightened around 6.5% over Europe, 10.4% over North America, and 7.7% over the rest of the world.
The finding is significant because it disagrees with satellite-based data, which has indicated that the rate of increase has been around 2% per year.
According to the new study, the discrepancy is probably the result of the satellites being unable to ‘sense’ blue light emitted by LEDs and to study light that is emitted parallel to the ground.

Nighttime light pollution:

Visible light emitted by many sources (except e.g. lasers) is divergent, so light emitted insufficiently downward could find its way into the sky.
Almost all surfaces in cities also reflect light, meaning a portion of entirely down-cast light will be reflected upwards, contributing to nighttime light pollution.
The researchers recommend light sources casting light at an angle below the plane of the horizon, capping the emissions of these sources and calibrating their output according to the total brightness at the spot being lit.

Situation over India:

A 2016 study reported that 19.5% of India’s population – the lowest fraction among G20 countries – experiences a level of skyglow that would at least keep the Milky Way galaxy out of sight and at most render “dark adaptation for human eyes” impossible.
The effects include stimulating the cone cells in human eyes, which is possible only when an environment is considered to be well-lit.
A 2017 study reported that between 2012 and 2016, India’s lit area increased by 1.07-1.09% and the average radiance of “stably lit areas” – e.g. excluding wildfires – increased by 1.05-1.07%.

The consequences:

The 2017 paper noted a curious pattern: “Regardless of historical or geographical context, humans tend to use as much artificial light as they can buy for about 0.7 percent of GDP.”
That is, even though LEDs have become more efficient, their utilisation hasn’t decreased, which in turn means the carbon emissions due to their production and use hasn’t decreased.
Numerous studies have also found artificial light at night affects both people and wildlife in important ways.
According to a 2003 report, lit beaches deter sea turtles from coming ashore to nest. A 2006 review found that skyglow keeps trees from sensing seasonal variations.
A 2017 study found that young burrow-nesting seabirds don’t take flight unless the nesting site becomes dark.
A 2019 study reported that clownfish eggs don’t hatch when exposed to artificial light at night, killing the offspring.
A 2020 study noted that skyglow interferes with multiple aspects of insect life and allows insect predators to hunt for longer.
By disrupting the circadian rhythm, artificial light at night can hamper the production of melatonin, an influential hormone in the human body with effects on sleep, moods and cognition.

Conclusion:

Parties to the Convention on Migratory Species adopted guidelines to address this specific problem at their meeting in Gandhinagar in 2020.
Recognizing that artificial light, particularly at night, is an emerging issue for the conservation of wildlife, astronomy and human health.