FEATHERY cirrus clouds are beautiful, but when it comes to climate change, they are the enemy. Found at high-altitude and made of small ice crystals, they trap heat - so more cirrus means a warmer world. Now it seems that, by destroying cirrus, we could reverse all the warming Earth has experienced so far.
In 2009, David Mitchell of the Desert Research Institute in Reno, Nevada, proposed a radical way to stop climate change: get rid of some cirrus. Now Trude Storelvmo of Yale University and colleagues have used a climate model to test the idea.
Storelvmo added powdered bismuth triiodide into the model's troposphere, the layer of the atmosphere in which these clouds form. Ice crystals grew around these particles and expanded, eventually falling out of the sky, reducing cirrus coverage. Without the particles, the ice crystals remained small and stayed up high for longer.
The technique, done on a global scale, created a powerful cooling effect, enough to counteract the 0.8 ?C of warming caused by all the greenhouse gases released by humans (Geophysical Research Letters, DOI: 10.1002/grl.50122).
But too much bismuth triiodide made the ice crystals shrink, so cirrus clouds lasted longer. "If you get the concentrations wrong, you could get the opposite of what you want," says Storelvmo. And, like other schemes for geoengineering, side effects are likely - changes in the jet stream, say.
Different model assumptions give different "safe" amounts of bismuth triiodide, says Tim Lenton of the University of Exeter, UK. "Do we really know the system well enough to be confident of being in the safe zone?" he asks. "You wouldn't want to touch this until you knew."
Mitchell says seeding would take 140 tonnes of bismuth triiodide every year, which by itself would cost $19 million.
If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.
Have your say
Only subscribers may leave comments on this article. Please log in.
Only personal subscribers may leave comments on this article
Subscribe now to comment.
All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
If you are having a technical problem posting a comment, please contact technical support.
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.