Volcanic eruptions, such as that of Mount Pinatubo in the Philippines in 1991, release sulfur-containing compounds into the stratosphere that temporarily cool Earth by reflecting solar radiation back into space. To combat climate change, some scientists have proposed simulating this impact of volcanoes by purposely injecting aerosols—clouds of particles suspended in a gas—into the stratosphere. However, according to a new study by atmospheric physicist Charlie Zender of the University of California, Irvine, this measure could make night skies brighter for most people, potentially causing adverse health effects and other drawbacks.
Previously, Zender studied how aerosols affect climate change using large models called Earth system models (ESMs). However, although ESMs readily make predictions about atmospheric temperatures, they don’t delve into sky brightness, Zender told Eos Monday while giving a poster presentation about his new work at the American Geophysical Union’s 2016 Fall Meeting in San Francisco.
To investigate the impact of injected aerosols on the brightness of the night sky, Zender created a new compact model, called NiteLite. It simulates the amount of light in the sky as seen from Earth’s surface and can be incorporated into ESMs. Using NiteLite, Zender compared the current amount of light in the sky from natural phenomena (like stars) and from artificial lighting created by people to how bright the sky would be if aerosols were added to the stratosphere.
Brighter Skies Could Hurt Our Health
According to Zender’s new model, in urban areas aerosols would scatter light coming from artificial sources on the ground, increasing sky brightness by 25% for the 95% of the world’s population who reside in these areas. The brighter skies would out glow the stars, making them no longer visible.
The increased brightness of the night sky could pose health risks for urban dwellers, Zender noted. Brighter skies disrupt our day-night cycle, called our circadian rhythm. Artificial light at night has been linked to depression, sleep disorders, and even an increase in breast and prostate cancer risks.
Brighter skies also adversely affect animals and plants, he added. For animals, artificial light can disrupt bird migration patterns, disorient sea turtles, and alter other behaviors such as mating and feeding. Too much artificial light can also keep trees from reacting properly to seasonal changes.
Stars Fade in Country Skies
In rural areas, where the only light at night comes from the stars, his model shows that the aerosols would decrease our ability to see stars by scattering their light so that we could no longer detect them. “You actually darken the sky,” Zender said. “This really surprised me.”
Whether the stars go dim in the country or vanish in the glare of city skies, “it’s not good for romantic evenings,” he quipped.
The Future of the Night Sky
Zender is planning to fine-tune his model so that he can look at what would happen to our night sky if we inject aerosols only over certain regions, such as at the polar ice caps.
“I think it’s interesting and instructive to look at all the possible impacts,” said Tami Bond, an environmental engineer at the University of Illinois at Urbana-Champaign who was not involved in the study.
Bond said that even if aerosol injection could help cool the planet, we need to take into account secondary effects, like changes to sky brightness, as we plan strategies to combat climate change.
“People place value on the ability to see the night sky,” said Bond. “If we engage in geoengineering, that’s one of the things we’re going to give up.”
—Sarah McQuate (email: [email protected]; @potassiumwhale), Science Communication Program Graduate Student, University of California, Santa Cruz
Correction, 14 December 2016: An editing error in an earlier version of this article introduced an inaccurate description of the aerosols. The article has been updated with a correct description.