Study examines effects of geo-engineering to combat climate change

Credit: Molly Swartz/Art Staff Credit: Molly Swartz/Art Staff

The prospect of rising temperatures and global climate change has been a burden on the shoulders of scientists for many years. Whether humans are the dominant cause or not, the problem is still present, and scientists and engineers are searching for a solution. One Carnegie Mellon graduate student is studying the possibilities of geo-engineering — perturbing the Earth’s climate system — in order to combat rising temperatures.

Kate Ricke, a Carnegie Mellon graduate student who started studying the climate during her undergraduate years at MIT, has been working with faculty in the department of engineering and public policy, looking at the possible outcomes of a geo-engineering technique known as solar-radiation management (SRM). This technique entails injecting suspended particles, or aerosols, into the stratosphere to increase the reflectivity of the Earth. As more solar radiation would be reflected back into space by these particles, less of it would reach the surface, which would result in a cooling effect on global temperatures.

A source of the SRM idea was the eruption of Mount Pinatubo in the Philippines in 1991. Volcanic ash and other aerosols were thrust into the stratosphere and remained there for up to three years as atmospheric circulation transported them across the globe. According to, scientists detected a short-term cooling effect on global temperatures as a result of the eruption. This event was naturally born, but it provided an interesting insight into the role of stratospheric particles on global surface temperatures.

“With the way things have been going with legislating emissions and the progress we’ve made towards abatement [of greenhouse gases], we need to at least know about geo-engineering — whether it’ll be useful in the future,” Ricke said.

The abatement of greenhouse gas emissions, Ricke further explained, would have to involve many countries taking action and reducing their emissions. However, with SRM, the Earth’s atmospheric circulation would take particles injected in any one spot and spread them out across the entire globe.

“Basically you’re all in if you do this type of geo-engineering. One person, if they have the means to put that stuff up there, could control the climate for everyone,” Ricke said. Potential effects on climate might be quite different for different regions around the world.

The study she worked on, which was recently published in Nature Geoscience, used computer models to simulate the effects of 54 different SRM scenarios on global temperature and precipitation. These simulations were then compared against the current projections on temperature and precipitation if no changes were made to greenhouse gas emissions. Researchers found that SRM could indeed prevent an increase in global temperatures, but it would also cause a global decrease in precipitation due to a reduction in water evaporation.

The major findings of the study, however, were the varying effects of SRM in different parts of the world. “If you set a criterion for what any given region would want to achieve using geo-engineering, you find that different regions prefer different things,” Ricke said. Different regions of the Earth have experienced temperature increase by different amounts and would therefore need different levels of SRM to compensate. Unfortunately, because of the global nature of SRM, it is extremely difficult to appease many different regions simultaneously. In addition, temperature effects cannot be easily localized because the atmosphere is always moving and mixing.

“It’s definitely an interesting thing to work on because there are a lot of open questions and not a whole lot of answers right now,” Ricke said. In general, the results of this study explore the possible benefits of SRM, but they also expose the complexities and uncertainties in this type of geo-engineering. SRM may result in a number of unexpected and unintended consequences, many of which would need much more experimental work and research to clarify before anyone can consider applying the technique in the real world.