A Global Sunshade

sunshade small A Global SunshadeIt’s one of the more controversial ideas out there for confronting climate change: Use high-flying airplanes to constantly replenish a layer of small particles in the stratosphere that would scatter sunlight back to space. But researchers have worried that such “sunshade geoengineering” could have unintended consequences for the world’s farmers. A preliminary modeling study, however, suggests the sunshade could actually help crop yields, at least in some places.

To evaluate the sunshade concept, a research team used three types of climate models. One assumed carbon dioxide levels are similar to today’s, the researchers report in Nature Climate Change. A second model doubled those levels, and a third posited doubled carbon dioxide, but with a layer of sulfate aerosols in the stratosphere that deflected about 2% of incoming sunlight away from the Earth. The simulated climate changes were then applied to crop models that are commonly used to project future yields.

The models suggested that a sunshade would lead to increased crop yields in most regions, both compared with current conditions and with the future projection of doubled carbon dioxide on its own. That’s because deflecting sunlight back to space reduces temperatures, but not carbon dioxide. “In many regions, future climate change is predicted to put crops under temperature stress, reducing yields. This stress is alleviated by geoengineering,” says Julia Pongratz of the Carnegie Institution for Science in Washington, D.C., one of the authors. “At the same time, the beneficial effects that a higher CO2 concentration has on plant productivity remain active.”

Even if the geoengineering would help crop yields overall, however, the models predict that some areas could be harmed by the geoengineering. And there are other risks that go beyond the direct impact on crop yields. For example, deployment of such systems might lead to political or even military conflict. Furthermore, these approaches do not solve the problem of ocean acidification, which is also caused by carbon dioxide emissions.

“The real world is much more complex than our climate models, so it would be premature to act based on model results like ours,” says Carnegie’s Ken Caldeira, another author. “But desperate people do desperate things,” he notes. That’s why “it is important to understand the consequences of actions that do not strike us as being particularly good ideas.”David Malakoff & press materials | January 25, 2012

Source: Pongratz, J., Lobell, D., Cao, L., & Caldeira, K. (2012). Crop yields in a geoengineered climate. Nature Climate Change DOI: 10.1038/nclimate1373

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