Carrying out geoengineering for several decades and then stopping would cause warming at a rate that will greatly exceed that expected due to global warming, according to published Feb. 18 in .

“The absolute temperature ends up being roughly the same as what it would have been, but the rate of change is so drastic, that ecosystems and organisms would have very little time to adapt to the changes,” said lead author , who did the work for her UW doctoral thesis.

The study looks at solar radiation management, a proposed method of geoengineering by spraying tiny sulfur-based particles into the upper atmosphere to reflect sunlight. This is similar to what happens after a major volcanic eruption, and many experts believe the technique is economically and technically feasible. But continuous implementation over years depends on technical functioning, continuous funding, bureaucratic agreement and lack of negative side effects.

The UW team used a global climate model to show that if an business-as-usual emissions pathway is followed up until 2035, allowing temperatures to rise 1°C above the 1970-1999 mean, and then geoengineering is implemented for 25 years and suddenly stopped, global temperatures could rise by 4°C in the following three decades, a rate more than double what it would have been otherwise, and one that exceeds historical temperature trends.

“The rate of standard projected global warming alone is going to be really detrimental to a lot of organisms, so if you increase that by a factor of 2 to 3, then those organisms are going to have an even harder time adapting or migrating,” said McCusker, now a postdoctoral researcher at the University of Victoria in Canada.

The results build on led by British researchers pointing to the risk of implementing and then stopping geoengineering. That study compared several climate models, showing that the result is not specific to any one model. The UW researchers used a single model with a more realistic scenario, where instead of simply decreasing the strength of the sun they actually simulated sulfate particles to stabilize the temperature, allowing a more precise look at the spatial and seasonal pattern of the response.

“The changes that will be needed to adapt to a warmer climate are really profound,” said co-author , a UW professor of atmospheric sciences. “The faster the climate changes, the less time farmers have to develop new agricultural practices, and the less time plants and animals have to move or evolve.”

The total amount of warming after stopping geoengineering would be largest in winter near the poles, but compared to typical historical rates of change they found that changes would be most extreme in the tropics in summertime, where there is usually very little temperature variation.

“According to our simulations, tropical regions like South Asia and sub-Saharan Africa will be hit particularly hard, the very same regions that are home to many of the world’s most food-insecure populations,” McCusker said. “The potential temperature changes also pose a severe threat to biodiversity.”

The researchers looked at different variables and found that the rate of warming is largely determined by the length of time that geoengineering is deployed and the amount of greenhouse gases emitted during that time, rather than by how sensitive the climate is to changes in greenhouse-gas concentrations.

“If we must geoengineer, it does not give us an excuse to keep emitting greenhouse gases,” McCusker said. “On the contrary, our results demonstrate that if geoengineering is ever deployed, it’s imperative that greenhouse gases be reduced at the same time to reduce the risk of rapid warming.”

The research was funded by the Tamaki Foundation, the National Science Foundation and the James S. McDonnell Foundation. Other co-authors are , a UW professor of atmospheric sciences, and , a former UW doctoral student now at the Massachusetts Institute of Technology.

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For more information, contact McCusker at 250-363-3456 or kemccusk@uvic.ca or Battisti at 206-543-2019 or battisti@uw.edu.

Adapted from a news release from the .

ÌìÃÀÓ°ÊÓ´«Ã½ researchers led the three-year project to gather leading thinkers and publish a snapshot of a field that they say is rapidly gaining credibility in the scientific community.

“In the past five years or so, geoengineering has moved from the realm of quackery to being the subject of scientific research,” said co-editor , a UW associate professor of atmospheric sciences. “We wanted to contribute to a serious intellectual discourse.”

Creating clouds over the ocean that would reflect back sunlight is the subject of a by Wood, whose research is on the interaction among air pollution, clouds and climate. He and co-author Tom Ackerman, a UW atmospheric sciences professor, look at what it would take to test the idea with a field experiment.

“I don’t want to prove it right, I just want to know if it’s feasible,” Wood said. “If you look at the projections for how much the Earth’s air temperature is supposed to warm over the next century, it is frightening. We should at least know the options. Is geoengineering feasible if there were to be what people call a ‘climate emergency’?”

Also explored in the journal issue is the idea of injecting reflective particles into the stratosphere, subject of a 2006 in Climatic Change by Nobel Prize-winning chemist Paul Crutzen and central to Seattle entrepreneur Nathan Myhrvold’s proposed . Yet another idea is of ocean microbes, though Wood said preliminary tests suggest this is not as successful at drawing carbon dioxide out of the atmosphere as its proponents had originally thought.

How to govern geoengineering is a topic of hot debate. In one , U.K. authors flesh out the so-called , which suggest how geoengineering could be regulated as a global public good. The five principles described in the paper concern the research, publication, assessment and deployment of geoengineering techniques.

Many of the authors spoke at the UW during a , and more attended a 2012 workshop where they developed their paper ideas.

While discussions were civil, Wood said, the contributors didn’t all agree. A UW philosopher questions whether geoengineering can even be described in the Oxford Principles as a global public good.

“Just spraying sulfates into the stratosphere is not the kind of thing that necessarily benefits everyone, so in that sense it seems a mistake to call it a global public good,” said co-editor , a UW philosophy professor who has written a book on ethics and climate change. There are decisions about how to conduct sulfate spraying, he writes, and potential tradeoffs between short-term benefits and long-term risks.

Gardiner also questions whether something should be done in people’s benefit but without their permission, and if accepting geoengineering as a necessary evil ignores other science or policy options.

He’s not the only social scientist to be looking at climate issues.

“A lot of people, from across the academy, are getting interested in the Anthropocene – the idea that we may have entered a new geological era where human influence is a dominant feature, and what that means for various issues,” Gardiner said.

The collection aims to prompt a serious academic discussion the editors say has so far been lacking.

“It’s an interdisciplinary discussion with an emphasis on the research angle – whether and how we should be researching geoengineering,” said co-editor Lauren Hartzell-Nichols, a UW lecturer in philosophy. “We hope it helps people think about this issue in a more interdisciplinary and integrated way.”

The seminars and workshop that led to the issue’s creation were supported by the UW College of the Environment.

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For more information, contact Wood at 206-543-1203 or robwood@atmos.washington.edu and Gardiner at 206-221-6459 or smgard@uw.edu.

atmospheric physicist describes a possible way to run an experiment to test the concept on a small scale in a comprehensive paper published this month in the journal .

The point of the paper — which includes updates on the latest study into what kind of ship would be best to spray the salt water into the sky, how large the water droplets should be and the potential climatological impacts — is to encourage more scientists to consider the idea of marine cloud brightening and even poke holes in it. In the paper, he and a colleague detail an experiment to test the concept.

“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 so-called marine cloud brightening is that adding particles, in this case sea salt, to the sky over the ocean would form large, long-lived clouds. Clouds appear when water forms around particles. Since there is a limited amount of water in the air, adding more particles creates more, but 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.

Marine cloud brightening is part of a broader concept known as geoengineering which encompasses efforts to use technology to manipulate the environment. Brightening, like other geoengineering proposals, is controversial for its ethical and political ramifications and the uncertainty around its impact. But those aren’t reasons not to study it, Wood said.

“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.

Wood and his colleagues propose trying a small-scale experiment to test feasibility and begin to 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 10 ships spread out across a 100 kilometer, or 62 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, where 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.

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.

“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.

There are 25 authors on the paper, including scientists from University of Leeds, University of Edinburgh and the Pacific Northwest National Laboratory. 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.

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For more information, contact Wood at 206-543-1203 or robwood2@u.washington.edu