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Caldeira Lab

Crop Yields in a Geoengineered Climate: Dr. Julia Pongratz

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Q = Caldeira, A = Pongratz

Q: Are there reasons why we might suspect that climate change might impact food security?

A: There definitely are. Studies looking at crop yields over the last decades have found that crop yields generally increase due to the technological progress we’ve had, but that this increase could actually be substantially larger if it weren’t for climate change in the past. Most notably, it’s the changes in temperature, the global warming, but also changes in precipitation that have led to a loss of yields over the last decades. And this loss in yields is also projected to continue under future climate change.

Q: So, some people have suggested that we can do things like put small particles in the stratosphere to do--reflect some sunlight and try to reverse the effects of climate change. Do these things seem physically possible?

A: These geoengineering schemes, in particular the solar radiation management you’re mentioning, have been frequently suggested, and by some members of the political and scientific community even as an alternative to reducing greenhouse gas emissions. And this makes it imperative to assess the risks of geoengineering, and one such risk could be that potentially the global food security might be negatively affected. And people have indeed said that geoengineering may pose a threat to billions of people.

Q: So do your results support this contention that these geoengineering proposals would threaten the food supply to billions of people?

A: In our study, we’ve simulated geoengineering in two different climate models and combined these climate simulations with a statistical crop model to get the changes in yields of maize, wheat, and rice. What we find is that under geoengineering as compared to a high CO2 world without geoengineering, the global crop yields are indeed higher. And the reason is mainly because the detrimental effects of increased temperatures is averted by geoengineering while the beneficial effects of CO2 fertilization, which increases plant productivity, can still act.

Q: So does this mean it would be a good idea to start putting particles in the sky tomorrow?

A: There’s much more research needed first. There’s two caveats identified by our study. One is, it may indeed seem that global yields increase substantially by geoengineering, but the gains and losses of crop yields are not uniformly distributed. There’s individual regions where yields go down. And in particular, if this is a vulnerable region with subsistence farming prevailing, then this may pose a risk to food security on the local scale. And also, geoengineering does not address the range of other issues associated with climate change such as ocean acidification, which may have an effect on global food security via marine food webs. And we are playing with a not completely understood complex climate system, which poses all kinds of other unanticipated risks. And therefore we believe that the safest option how to reduce risks in global food security is to reduce emissions of greenhouse gases.

Q: Thank you very much, Julia, for telling us about your recent work.

A: Thank you, Ken.


Pongratz, J., D. B. Lobell, L. Cao, , and K. Caldeira (2012), Crop yields in a geoengineered climate, Nature Climate Change, doi: 10.1038/NCLIMATE1373


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