When Katharine Ricke tells nonscientists what she's currently investigating, they're "often bewildered," she says, because "it sounds like something out of a sci-fi movie." The fourth-year Ph.D. student in the Department of Engineering and Public Policy of Carnegie Mellon University  (CMU) in Pittsburgh, Pennsylvania, is studying geoengineering -- specifically, the possibility of intentionally manipulating Earth's climate to compensate for global warming.
"It sounds like a bad idea, I think, to most people the first time they hear about it," Ricke says. There is, she says, a lot of resistance from the environmental sciences community. When Granger Morgan, her Ph.D. adviser, suggested that she pursue the idea, even her own reaction wasn't positive. "But the more that I learned about it, the more I saw this was definitely an under-researched topic," she says. "There is the potential that someone could do it, and who knows what would happen because we never bothered to study it."
Ricke studies the possibility of reflecting part of the sun's light back into space to compensate for warming caused by increasing levels of greenhouse gases, an approach known as solar radiation management (SRM). The particular technology Ricke is looking at would block incoming sunlight by placing a layer of aerosols or reflective particles into the stratosphere. It's controversial, in part because "if someone does this, it affects the climate in the whole world," Ricke says. And it's fast: "You see a global cooling effect almost immediately."
Because it compensates for changes in infrared atmospheric radiation fluxes caused by greenhouse gases with intentional changes in solar radiation fluxes, SRM "doesn't just bring the climate back to where it was in the past," Ricke says. It would compensate for climate change in different regions differently, affecting temperature and hydrological patterns regionally. "Some regions might dry out with SRM relative to a high carbon dioxide world with no SRM, some might get wetter, some may have the effects they experience from global warming exacerbated, and many may have those effects mitigated but to different extents."
Ricke works to better understand what levels of SRM different parts of the world are likely to prefer, and who would come out winners and losers for a given level of global SRM. She models the impact of SRM strategies on regional hydrological patterns using climateprediction.net, a distributed computing system that allows climate researchers to harness the power of unused personal computers around the world.
If you make the assumption that what's optimal for a given region is "whatever makes it most like the past, then almost always every region is better off with some level of solar radiation modification," Ricke says. But the regional responses and the drying out of the hydrological cycle at the mean, global level make the compensation imperfect and nonuniform, she adds. Her research has shown that different regions would likely prefer different levels of solar radiation management. And "the longer you keep applying this imperfect compensation, at higher and higher levels to compensate for rising greenhouse gas concentrations in the atmosphere, the more imperfect regional responses become." As a consequence, climate geoengineering raises sensitive policy and international relations issues: Who gets to decide, how can equity be ensured, and who is liable for damages?
Ricke has been fascinated by Earth and other planets for as long as she can remember. She earned an undergraduate degree in ocean and atmospheric physics from the Earth, Atmospheric and Planetary Sciences Department  at the Massachusetts Institute of Technology in Cambridge, taking a minor in public policy. "I've always had a strong environmental streak, and so environmental policy was a natural side interest for me," she says.
- A report from the British Royal Society on Geoengineering the climate: science, governance and uncertainty 
- The Royal Society also recently launched a major study on the governance of geoengineering 
- The Climate Response Fund  in the United States
- Hack the Planet , by Science magazine reporter Eli Kintisch
Climate geoengineering is new and controversial, so starting work on the topic poses real challenges. For advice on getting started, see the informational box, below.
Upon graduating, in 2004, Ricke felt she needed to step back for a while. "I was at a point where I didn't know if I wanted to be a scientist. ... I wasn't sure whether academia would offer opportunities to do things that were real-world relevant." She took an analyst position at Abt Associates , a research and consulting firm based in Cambridge. At Abt, she analyzed environmental data sets to support the U.S. Environmental Protection Agency in its decision-making and presentation of information to the public.
Eventually, she started to look for "a bigger challenge," she says. She sought a graduate program that would allow her to do work that was both technically challenging and policy-relevant. She found it at CMU, and began her graduate training there in 2007.
Originally, Ricke set out to study the impacts and costs of geoengineering's consequences -- changes in temperature, precipitation, atmospheric composition, and intensity of sunlight -- on the productivity of natural and managed ecosystems. But "then it turned out that no one had really done that much on the climate modeling side yet, so I didn't really have the background of literature I needed to build off of to do impacts analysis," she says. When an opportunity arose to collaborate with climate dynamics researcher Myles Allen of the Department of Physics  at the University of Oxford in the United Kingdom, that seemed a good void to try and fill.
Working on a controversial topic such as climate geoengineering has plusses and minuses, Ricke says. Because it's so new and provocative, opportunities to present at conferences are easier to come by. But "because it's controversial, it may be a little bit harder to get all the reviewers onboard" when trying to publish scientific articles.
Back in November, Science Careers explored rising opportunities for natural and social scientists to study climate change and further our understanding of its likely impacts. This week, Science Careers complements this past feature on Careers in Climate Change Research  by looking into ongoing research efforts aimed at actually curbing carbon dioxide emissions and reducing global warming.
Read our two other Mitigating Climate Change feature articles:
In Researching Carbon-Neutral Buildings , freelance science and environmental writer Naomi Lubick reports on how new research in building technology aims to boost energy efficiency and reduce carbon emissions from commercial buildings and homes. The research potential in the field is enormous, and job prospects are on the rise, Lubick found.
The emerging technology of carbon capture and storage, which aims to capture carbon dioxide generated by industrial power plants and store it underground before it reaches the atmosphere, is also a growing research area. In Examining Carbon Capture and Storage , freelance science writer Sara Coelho describes what it's like to work in the competitive, fast-paced, and interdisciplinary research field.
What makes solar radiation management most attractive is the time scale. "If you want to take carbon dioxide out of the atmosphere, you either have to find a technology to directly capture it, which is a slow process, or you have to cut emissions and wait for the concentrations in the atmosphere to go down, which is also a very slow process," Ricke says. A climate geoengineering option like SRM, in contrast, "has the potential to cool down the planet very quickly."
The downside is that solar radiation management treats a symptom -- warming -- and not the underlying cause, so it leaves a host of other symptoms untreated. "Solar radiation management to cool down the planet is never going to perfectly compensate for the changes in the global ecological cycle that happen with rising greenhouse gases," Ricke says. And "solar radiation management doesn't address the problem of ocean acidification at all." Furthermore, there could be serious side effects, like damaging the ozone layer. "Everyone who's studying this right now acknowledges that there's probably a whole bunch of things that could happen that we even haven't thought of yet. Just that uncertainty makes it essentially scary."
What makes it even scarier is that "it's something that is possible," Ricke says. "Because climate geoengineering like this is pretty cheap to actually do, there is the potential that one nation or one small group of nations or even some sub-national entity could do this themselves." Currently, climate geoengineering falls outside the scope of international law. Last March, during the Asilomar International Conference on Climate Intervention Technologies , science and policy experts met to discuss  the risks associated with climate-intervention experiments and propose voluntary standards for the international scientific community. But there's far more work to be done, and there's always the risk for standards to be ignored.
"I don't think we know enough about its potential benefits and side effects to say yet whether [solar radiation management] could be a good thing for humanity as a whole [and] for the planet as a whole," Ricke says. She is deeply concerned about the inequities likely to occur in implementing climate geoengineering plans. Yet, if those interventions were informed by a sound and fair decision-making process, "I don't think that would necessarily be a bad thing," she says. "The sad fact is that we might need it, and so [it's] best to know everything that we can about it."
Geoengineering research has offered Ricke both the scientific challenges and the real-world focus she was seeking. She intends to pursue a career at the boundary of science and policy in climate, energy, and the environment, preferably in academia. "For me, my dissertation work on geoengineering is more of a case study of how to approach making a contribution to a topic like this, in which there are a lot of unknowns about the science still, but there is nonetheless a need to start developing a policy framework to address the problem immediately," she says.
Geoengineering also gave Ricke an opportunity to learn skills that are applicable elsewhere, such as her computer-modeling skills. "I get to work on typical Ph.D. research in terms of the technical skills and knowledge I'm building, but with ... more of a chance to learn how to frame my work so it's relevant to a larger, often contentious debate going on in society about this topic," she says. She gets to observe closely, and even participate in, this debate as it plays out among more senior folks, she adds. "Because it's just recently that people have decided that this topic is worthy of serious research time, I think that I got in on it just at the right time to be a part of a constantly evolving and very interesting discussion in the scientific community."
The idea of cooling the planet through the deliberate, large-scale modification of the environment isn't new. Frustration over stalled greenhouse negotiations and a growing sense of urgency about climate change have pushed the idea to the fore. But it remains a marginal and risky topic to base a career on.
"Right now, there is no U.S. federal program" to support research in geoengineering, says Ken Caldeira of the Department of Global Ecology at the Carnegie Institution  in Stanford, California, who studies the consequences of geoengineering proposals as part of a broader research program. Nonetheless, "some people might have individual grants related to geoengineering." Ricke's work is funded by the Climate Decision Making Center  at CMU, and she is supported by a graduate research fellowship from the National Science Foundation. According to a report  recently released by the U.K. Parliamentary Office of Science and Technology, less than $1 million of public money is currently directly supporting geoengineering research in the United States.
The picture is broadly the same overseas: in the United Kingdom, the Royal Society recently called for a national 10-year, £10 million per annum geoengineering research program, but funding has not been approved. The Engineering and Physical Sciences Research Council and Natural Environment Research Council, however, recently announced  the availability of as much as £3.5 million for geoengineering research projects.
Limited funding means that "there's not that many groups doing work in this area," Caldeira says, and the few that do usually do it as a side project. "If you just look at the published papers, there's a small handful of groups in the United States, a few in the U.K., a few in Germany," Caldeira adds. Yet, there is much potentially important work to be done. "Most of the focus has been among climate scientists, who are mostly running general circulation models, but there are important questions related to atmospheric chemistry, to ecosystem responses, to issues associated with cloud dynamics," Caldeira says.
Geoengineering is a wide and interdisciplinary topic, encompassing climate and environmental science, engineering, and social and political issues. You can approach the topic from any of these directions. Caldeira recommends that scientists gain "a broad scientific background relevant to what they really would like to study."
"In a way, it's an easy topic to get into because there is a small literature, and so in a few weeks they could read almost all of the papers," Caldeira says. That's a great start -- but don't stop at reading, he advises. "When they read a paper that's similar to something that they would like to do, they should send an e-mail to the author." Ask questions and make suggestions, he suggests. "Be a little bit pushy."
But beware the risks. Don't put all your eggs in the climate geoengineering basket, as that could make it difficult to find a good job later on. "Maybe in the next 5 years everyone will decide it makes no sense, and that will kind of disappear," Caldeira says. This makes your strong footing in one of the key underlying disciplines all the more important. "If you have a good grounding in some aspect of environmental science and then, as part of your work, you are applying that understanding to geoengineering problems, I think that most people would think that's fine."
Photo (top): Ann Baekken 
Elisabeth Pain is contributing editor for South Europe.