From: Bobbie Edwards, MONGABAY.COM, More from this Affiliate
Published January 15, 2014 12:19 PM

Climate fail: Geoengineering would cool planet, but screw up rainfall patterns

For decades, scientists have been grappling with the consequences of climate change and working toward viable solutions. Climate engineering, also known as geoengineering, is the most controversial possible solution.

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Currently, one of the most talked about geoengineering ideas is Solar Radiation Management (SRM), which intends to block shortwave solar radiation, thus cooling the Earth to offset rising temperatures. In other words, SRM may be one way in which global temperatures could be artificially stabilized. But a new study in the Journal of Geophysical Research: Atmospheres, finds that while SRM-style geoengineering may succeed in cooling the Earth, it would also disrupt precipitation patterns around the world.

One popular SRM idea is to fire sulfates into the atmosphere, simulating what happens during a volcanic eruption, when plumes of debris are emitted into the atmosphere and effectively act as shields against solar radiation. However, large volcanic events are often accompanied by negative effects on local and even global environmental systems. For instance, the 1991 eruption of Mt. Pinatubo in the Philippines weakened the water cycle and depleted the stratospheric ozone layer above the Arctic pole for two years.

Climate change is generally expected to increase global precipitation because the heat trapped near Earth's surface leads to higher rates of evaporation. But using SRM is expected to decrease rainfall. Therefore to better understand what rainfall may look like in the future under various scenarios, scientists led by Simone Tilmes of the National Center for Atmospheric Research (NCAR) manipulated 12 of the world's leading climate simulation models via the Geoengineering Model Intercomparison Project (GeoMIP).

Model accuracy is important, and those used by this team were vetted against past observations and shown to correctly predict previous long-term climatic observations. However, their accuracy diminished when used for more specific weather events.

"For instance, over the last 100 year period, most of the models showed the observed temperature increase;" said Tilmes, "however there are still uncertainties in the detail...Climate models cannot predict specific weather phenomena, but they can predict that for instance, hurricanes become stronger, rainfall extremes increase, and that can be compared if we have long observational records."

The team began by setting global CO2 levels at an extremely high level: 1,120 parts per million (ppm) or four times the pre-industrial level of around 280 ppm. This level is on the extreme side of projections for the end of this century.

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Volcano cloud image via Shutterstock.

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