Slowing Global Warming With Cloud Geoengineering

April Flowers for – Your Universe Online

Imagine futuristic ships shooting salt water into the clouds over the world’s oceans to create clouds that reflect sunlight. Sounds like science fiction, but it could be reality before too long.

An international team of researchers is taking a second look at this controversial idea to slow global warming effects and has published their concept in this month’s Philosophical Transactions of the Royal Society.

University of Washington atmospheric physicist Rob Woods describes a possible way to run a small-scale experiment to test the concept, including the latest study on what type of ship to use, how large the water droplets should be and the climatological impacts of such cloud seeding. He and his colleagues hope that the paper will encourage more scientists to consider the idea and even poke holes in it.

“What we’re trying to do is make the case that this is a beneficial experiment to do,” Wood said. With enough interest in cloud brightening from the scientific community, funding for an experiment may become possible, he said.

The theory behind this new kind of cloud seeding, called marine cloud brightening, is that adding particles, in this case sea salt, to the sky over the ocean would form large, long living clouds. Clouds appear when water forms around particles, and since there is a limited amount of water in the air, adding particles creates more, albeit smaller, droplets.

“It turns out that a greater number of smaller drops has a greater surface area, so it means the clouds reflect a greater amount of light back into space,” Wood said. That creates a cooling effect on Earth.

Geoengineering, of which marine cloud brightening is a part of, encompasses efforts to use technology to manipulate the environment.  Geoengineering mostly refers to the deliberate and large-scale engineering and manipulation of the planetary environment to combat or counteract changes in atmospheric chemistry. So far, the scientific community at large feels that geoengineering is largely unproven and that reliable cost estimates have not been published. To date, no large-scale geoengineering projects have been undertaken, and there are many critics in the scientific community.

Like other geoengineering proposals, brightening is controversial for its ethical and political ramifications and the uncertainty around its impact. Woods asserts that these are not reasons to avoid studying the issue, however.

“I would rather that responsible scientists test the idea than groups that might have a vested interest in proving its success,” he said. The danger with private organizations experimenting with geoengineering is that “there is an assumption that it’s got to work,” he said.

The team proposes trying a small-scale experiment to test feasibility and study the effects. They suggest starting by deploying sprayers on a ship or barge to ensure that they can inject enough particles of the targeted size to the appropriate elevation. An airplane equipped with sensors would study the physical and chemical characteristics of the particles and how they disperse.

Further suggestions include the use of additional airplanes to study how the cloud develops and how long it lasts. The final phase of testing would send out five to 10 ships across a 100-kilometer stretch. The resulting clouds would be large enough that scientists could use satellites to examine them and their ability to reflect light.

Based on studies of pollutants, which emit particles that cause a similar reaction in clouds, scientist know that the impact of adding particles to clouds is short-lived, so there would not be a chance of long-term effects from the marine brightening.

In the world of climate scientists, however, it would be an unusual experiment, where scientists observe rather than trying to actually change the atmosphere. The team feels that it would advance knowledge of how particles impact the climate, as well as test the geoengineering idea.

Ship trails are one phenomenon that inspired marine cloud brightening. Ship trails are 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.

But in some cases 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, responding in part to the feeling that geoengineering projects present moral hazards, and the long term effects of the plan are unknown.

“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.

Image 2 (below): A conceptualized image of an unmanned, wind-powered, remotely controlled ship that could be used to implement cloud brightening. Credit: John McNeill, University of Washington

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