By Maggie Liu

Original article:

Lockdown induced night-time light dynamics during the COVID-19 epidemic in global megacities

Gang Xu, Tianyu Xiu, Xi Li, Xinlian Liang, Limin Jiao

By now, I’m sure we’re all sick of hearing the words “COVID” and “lockdown.” After being stuck inside for a year, the last thing I wanted to do was stay inside some more. But what if I told you that the lockdown was actually really good for the environment? I’m sure many of us know that water and air quality have increased across the world. “The coronavirus pandemic is shutting down industrial activity and temporarily slashing air pollution levels around the world,” says a The Guardian article from last year (The Guardian, 2020), yet there’s been a decrease in one more type of pollution that no one’s talking about: light pollution.

“The Milky Way is hidden from more than one-third of humanity, including 60% of Europeans and nearly 80% of North Americans,” says a paper published by Science Advances (Falchi et al., 2016). Light pollution can have severe detrimental effects on humans, most notably the suppression of melatonin, which can then lead to an increased risk of breast cancer, as well as harmful effects on the ecosystem, such as the reduction of nocturnal pollinators (IAU, 2021). Though we, as a society, are unable to truly turn off all lights at night, the lockdowns associated with the COVID-19 pandemic have actually helped us to dim them. In a report published by the International Journal of Applied Earth Observations and Geoinformation, a research team from Wuhan University found that 82% of the world population lived in areas where lights had been dimmed due to the lockdown (Xu et al., 2021). The team, led by Gang Xu, analyzed twenty megacities (cities with a population of at least ten million people) from around the world, all of which had implemented some sort of lockdown procedure during the pandemic.

Using a data-processing tool from NASA called Black Marble, Xu and his team were able to determine which cities showed an overall decrease, increase, or no change in radiance. They found that ten cities (Mumbai, Dhaka, Manila, Karachi, Kolkata, New York, Tokyo, Mexico City, Ho Chi Minh City, Los Angeles) had an obvious decrease in radiance, five cities (Johannesburg, Bangkok, Buenos Aires, Cairo, Beijing) exhibited no change or radiance differences that didn’t fit a pattern, and five cities (São Paulo, Paris, Moscow, London, Seoul) even exhibited an increase in radiance. In general, however, the trends are consistent, with the radiance decreasing after the establishment of lockdown procedures and centralized around the city centers, where most shops and businesses were closed or less-frequented during lockdown.

But why did some cities increase in radiance? The answer lies in the citizens’ COVID preparations. For Seoul and London, Xu’s team found that the radiance of the cities had already decreased a week before lockdown procedures, rising during the time of the study, because ‘since the epidemic had spread to the country or the city, urban residents had reduced their social activities in advance’ (Xu et al., 2021). Meanwhile, the reason for Beijing’s unpatterned radiance was due to the coincidence of the lockdown with Chinese New Year. The increase in city lights, Xu’s team found, correlated closely to the holiday and decreased soon afterwards.

The COVID-19 pandemic changed many things for us. In particular, it changed how we, as humans, looked at the impact that we leave on the world. The study carried out by Xu’s team showed us that the COVID lockdowns, though meant to curb the spread of the disease, also helped to decrease light pollution across the world. And why should we care about light pollution? Because it has detrimental effects on human health, as well as the health of the nighttime ecosystem. Though this study was only limited to twenty megacities, and even then, not every city exhibited a decrease in radiance, it still highlighted an important aspect of light pollution that bears remembering: it was caused by us, so it can only be fixed by us.

References

Falchi, F., Cinzano, P., Duriscoe, D., Kyba, C. C. M., Elvidge, C. D., Baugh, K.,
Portnov, B. A., Rybnikova, N. A., & Furgoni, R. (2016, June 1). The new world atlas of artificial night sky brightness. Science Advances.
https://advances.sciencemag.org/content/2/6/e1600377.

Guardian News and Media. (2020, March 23). Coronavirus pandemic leading to huge drop in air pollution. The Guardian.
https://www.theguardian.com/environment/2020/mar/23/coronaviruspandemic-leading-to-huge-drop-in-air-pollution.

International Astronomical Union. (2021, April). Dark and Quiet Skies for Science and Society. Paris.