Geoengineering clouds to slow global warming
study effects. The test should start by deploying sprayers on a ship or barge to ensure that they can inject enough particles of the targeted size to the appropriate elevation, Wood and a colleague wrote in the report. An airplane equipped with sensors would study the physical and chemical characteristics of the particles and how they disperse.
The next step would be to use additional airplanes to study how the cloud develops and how long it remains. The final phase of the experiment would send out five to ten ships spread out across a 100 kilometer, or sixty-two mile, stretch. The resulting clouds would be large enough so that scientists could use satellites to examine them and their ability to reflect light.
Wood said there is very little chance of long-term effects from such an experiment. Based on studies of pollutants, which emit particles that cause a similar reaction in clouds, scientists know that the impact of adding particles to clouds lasts only a few days.
Still, such an experiment would be unusual in the world of climate science, in which scientists observe rather than actually try to change the atmosphere.
Wood notes that running the experiment would advance knowledge around how particles like pollutants impact the climate, although the main reason to do it would be to test the geoengineering idea.
A phenomenon that inspired marine cloud brightening is ship trails: clouds that form behind the paths of ships crossing the ocean, similar to the trails that airplanes leave across the sky. Ship trails form around particles released from burning fuel.
In some cases, however, ship trails make clouds darker. “We don’t really know why that is,” Wood said.
Despite increasing interest from scientists like Wood, there is still strong resistance to cloud brightening.
“It’s a quick-fix idea when really what we need to do is move toward a low-carbon emission economy, which is turning out to be a long process,” Wood said. “I think we ought to know about the possibilities, just in case.”
The authors of the paper are treading cautiously. “We stress that there would be no justification for deployment of [marine cloud brightening] unless it was clearly established that no significant adverse consequences would result. There would also need to be an international agreement firmly in favor of such action,” they wrote in the paper’s summary.
The lead author is John Latham of the National Center for Atmospheric Research and the University of Manchester, who pioneered the idea of marine cloud brightening.
Wood’s research was supported by the UW College of the Environment Institute.
— Read more in John Latham et al., “Marine cloud brightening,” Philosophical Transactions of the Royal Society A 370, no. 1974 (13 September 2012): 4217-62 (doi: 10.1098/rsta.2012.0086)
