March 4, 2008 -- Proposals to mask global warming by mimicking the cooling effects of volcanic eruptions have hit a little snag: Far more dust could be needed than expected.
New modeling of the effects of sunlight-reflecting sulfate particles of different sizes injected into the stratosphere to reduce the sunlight reaching Earth's surface suggest that at least 50 percent more faux volcanic dust would be required. That makes the task a tad more taunting.
What's more, the authors of the new study caution that the side effects of such a massive 'geoengineering' project are still unknown.
"If you read the papers that people are writing, they are trying to be very cautious about it," said Philip Rasch of the National Center for Atmospheric Research in Boulder, Colo.
Rasch is the lead author of a paper on the modeling experiment which appeared in the latest issue of the journal Geophysical Research Letters.
What Rasch showed in his experiment is that closely mimicking volcanoes is not necessarily desirable.
"People produce estimates based on using volcanic eruptions as analogues," said Rasch. "It's not a perfect analogy."
For one thing a volcano like Mount Pinatubo in the Philippines may have poured a lot of sun-reflecting sulfate particles into the stratosphere, but it did so from only one location and for a short period of time.
"We wouldn't do it that way with geoengineering," said Rasch.
In his model Rasch used an idealized scenario to simulate the injection of sulfates uniformly in equatorial regions, at all longitudes, at a constant rate over time. In the real world, that would probably entail the use of airplanes, balloons, artillery or other technology to put the sulfates gradually into the stratosphere.
What's more, the modeling showed that size matters. Twice as many large sulfate particles -- like those created by volcanoes -- would be needed to do the same cooling as smaller manmade particles.
"This is what I would call the first of the next generation of geoengineering simulations," said climate researcher Ken Caldeira of Stanford University. This kind of detail is essential to truly evaluate the costs and feasibility of geoengineering.
So far, it looks pretty affordable, said Rasch. Back of the envelope calculations suggest such efforts are more economical than a massive restructuring of the world's economy to run on fewer fossil fuels.
"It's not the cost of it that is a big problem," said Rasch about geoengineering. "Yet if we do nothing we still have a big problem."
Also, such geo-engineered cooling does nothing to halt the ongoing increasing carbon dioxide from fossil fuel burning which causes other problems -- like making the oceans more acidic. As Rasch adds, "geoengineering is not a complete solution" and he would prefer that we cut emissions.
"I think this paper shows that that this sort of geoengineering scheme isn't perfect," agrees Caldeira. "It doesn't return the Earth to a pristine state."
Still, Caldeira said, it's better than the version of Earth we'll get with much higher carbon dioxide levels without any geoengineering.
Related Links:
Larry O'Hanlon's blog: Earth Impacts
National Center for Atmospheric Research
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