Geoengineering: A Whiter
Sky
Washington, D.C. —
One idea for fighting global warming is
to increase the amount of aerosols in the atmosphere, scattering incoming solar
energy away from the Earth’s surface. But scientists theorize that this solar
geoengineering could have a side effect of whitening the sky during the day. New
research from Carnegie’s Ben Kravitz and Ken Caldeira indicates that blocking 2%
of the sun’s light would make the sky three-to-five times brighter, as well as
whiter. Their work is published June 1st in Geophysical Research
Letters, a journal of the American Geophysical Union.
Carbon dioxide emissions from
the burning of coal, oil, and gas have been increasing over the past decades,
causing the Earth to get hotter and hotter. Large volcanic eruptions cool the
planet by creating lots of small particles in the stratosphere, but the
particles fall out within a couple of years, and the planet heats back up. The
idea behind solar geoengineering is to constantly replenish a layer of small
particles in the stratosphere, mimicking this volcanic aftermath and scattering
sunlight back to space.
Using advanced models, Kravitz
and Caldeira—along with Douglas MacMartin from the California Institute of
Technology—examined changes to sky color and brightness from using sulfate-based
aerosols in this way. They found that, depending on the size of the particles,
the sky would whiten during the day and sunsets would have afterglows.
Their models predict that the
sky would still be blue, but it would be a lighter shade than what most people
are used to looking at now. The research team’s work shows that skies everywhere
could look like those over urban areas in a world with this type of
geoengineering taking place. In urban areas, the sky often looks hazy and
white.
“These results give people one
more thing to consider before deciding whether we really want to go down this
road,” Kravitz said. “Although our study did not address the potential
psychological impact of these changes to the sky, they are important to consider
as well.”
There are several larger
environmental implications to the group’s findings, too. Because plants grow
more efficiently under diffuse light conditions such as this, global
photosynthetic activity could increase, pulling more of the greenhouse gas
carbon dioxide out of the atmosphere. On the other hand, the effectiveness of
solar power could be diminished, as less sunlight would reach solar-power
generators.
“I hope that we never get to
the point where people feel the need to spray aerosols in the sky to offset
rampant global warming,” Caldeira said. “This is one study where I am not eager
to have our predictions proven right by a global stratospheric aerosol layer in
the real world.”
__________________
The Department of Global Ecology was established in 2002 to
help build the scientific foundations for a sustainable future. The department
is located on the campus of Stanford University, but is an independent research
organization funded by the Carnegie Institution. Its scientists conduct basic
research on a wide range of large-scale environmental issues, including climate
change, ocean acidification, biological invasions, and changes in
biodiversity.
The Carnegie Institution for Science (carnegiescience.edu) is a private,
nonprofit organization headquartered in Washington, D.C., with six research
departments throughout the U.S. Since its founding in 1902, the Carnegie
Institution has been a pioneering force in basic scientific research. Carnegie
scientists are leaders in plant biology, developmental biology, astronomy,
materials science, global ecology, and Earth and planetary
science.
Natasha
T. Metzler
Science
Writer
Carnegie
Institution for Science
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