Global sunscreen won't save corals

http://www.eurekalert.org/pub_releases/2009-06/ci-gsw061609.php

Public release date: 16-Jun-2009
Contact: Ken Caldeira
Carnegie Institution

Palo Alto, CA— Emergency plans to counteract global warming by artificially shading the Earth from incoming sunlight might lower the planet's temperature a few degrees, but such "geoengineering" solutions would do little to stop the acidification of the world oceans that threatens coral reefs and other marine life, report the authors of a new study in the journal Geophysical Research Letters*. The culprit is atmospheric carbon dioxide, which even in a cooler globe will continue to be absorbed by seawater, creating acidic conditions.

"There would be a slight reduction in this problem, because land plants would be expected to be able to grow more vigorously in a high CO2, but cool world," says Ken Caldeira of the Carnegie Institution's Department of Global Ecology, a co-author of the study with lead author Damon Matthews of Concordia University, Canada, and Carnegie geochemist Long Cao. Land plants and soils would hold onto more carbon in this scenario, so less would find its way into the oceans. "However this expansion of the land biosphere, while it's a slight help to ocean acidification is not enough to make a big difference."

A widely-discussed proposal for countering warming with geoengineering involves injecting small, reflective particles into the upper atmosphere. This would partially block incoming sunlight before it reached the Earth's surface, lowering global temperatures just as volcanic ash from the Mount Pinatubo did following its eruption in 1991. But critics have warned that such a scheme might also alter rainfall patterns, damage the planet's ozone layer, or have other unexpected effects.
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