Geoengineering Could Turn Skies White

Efforts to reflect away the sun's rays might also
make the sky whiter, one of many reasons some distrust such
geoengineering schemes

















COLOR CHANGE: Blue skies could
turn white if geoengineering schemes are every employed to reflect away
the sun's rays using sulfate particles, mimicking a volcanic eruption.
Image: Wikimedia Commons/Merikanto







Showcasing more than fifty of the most provocative, original, and
significant online essays from 2011, The Best Science Writing Online
2012 will change the way...








The white haze that hangs over many major cities could become a
familiar sight everywhere if the world decides to try geoengineering to
create a cooler planet.




Scientists have long suspected that one oft-discussed geoengineering
technique -- shooting tiny sulfate particles into the upper atmosphere
to deflect sunlight -- could turn the blue sky white. Nature has already
provided a basic proof of concept. When Mount Pinatubo erupted in the
Philippines in 1991, spewing tons of sulfate particles in the
atmosphere, it temporarily whitened the sky.




Now a new study by researchers at the Carnegie Institution for Science
attempts to determine just how big the effect from man-made
geoengineering would be.




Adding enough sulfate to the stratosphere to block 2 percent of the
sun's light would make the sky three to five times brighter, they report
in a paper that will be published in the journal Geophysical Research Letters.


That is roughly the level of sulfate geoengineering needed to
counteract the warming that would result if the level of carbon dioxide
in the atmosphere climbed to 560 parts per million, up from roughly 390
ppm today.


The world might be cooler, but blue skies would become a little less
blue, the scientists report. Even remote, sparsely inhabited areas would
lie under a whitish sky resembling the haze that now blankets cities
like Paris.


And the injection of a continuous stream of sulfate particles would lend sunsets a man-made afterglow.


"People who are used to living in New York might not notice a
difference, but people in the mountains might notice a difference," said
lead author Ben Kravitz, a postdoctoral researcher at the Carnegie
Institution.


"What happens when you put a layer of sulfate aerosols into the
stratosphere, they scatter light. But they don't scatter light equally.
Depending on the size of the particle, they might scatter blue light
differently than red light."




It is that scattering effect that would change the sky's appearance, he said.


Some people might not notice. Others might not care. But even folks who
can't tell a picture-postcard blue sky from its milky, geoengineered
cousin might be able to detect other side effects of using sulfate to
cool the planet.




Blocking just 2 percent of sunlight that would normally reach the Earth
-- the scenario depicted in the study -- would probably be enough to
create measurable drops in energy created by concentrated solar thermal
power systems, which rely on direct sunlight.




But it could be a boon to plants, which showed a small but measurable uptick in growth in the months after Mount Pinatubo erupted in 1991.




That's because injecting sulfate particles into the atmosphere -- by
volcano or man-made methods -- scatters enough of the sun's rays to
increase the diffuse sunlight many plants thrive on. The resulting
uptick in photosynthesis would likely increase the amount of carbon
pulled from the atmosphere by plants, researchers said.




Majority frowns on geoengineering -- poll


Meanwhile, a poll released this week by the Brookings Institution
suggests that Americans are concerned about the safety and effectiveness
of geoengineering.




Sixty-five percent of participants said they somewhat or strongly disagree that if global warming takes place, "scientists would be able to find ways to alter the climate in a way that limits problems."


A slimmer majority, 45 percent, disagreed with the notion that
scientists could develop "atmospheric engineering" methods to cool the
planet.




But most of the 887 participants in the survey -- 69 percent -- said
they "strongly" or "somewhat" believed the harm from adding material to
the atmosphere would outweigh the benefits. The poll carries a margin of
error of 3.5 percent.





Source:-

http://www.scientificamerican.com/article.cfm?id=geoengineering-could-turn-skies-white