The “Right Dose” Of Sun Dimming Could Cut Global Warming Effects In Half, Study Says

Solar geoengineering works by projecting aerosol particles into the upper atmosphere in order to mitigate the effects of the sun on increasing global temperatures. DuToVision/Shutterstock

New research out of Harvard suggests that the “right dose” of solar geoengineering (SG) – spraying tiny reflective particles into the upper atmosphere to filter the Sun’s energy and reflect incoming sunlight – could cool the planet and curb the effects of climate change without adversely impacting some regions.

Solar radiation management (SRM) builds on how volcanic eruptions emit aerosols into the atmosphere, the idea being to inject aerosols into the stratosphere to act as a chemical “sunshade” that reflects and cools the planet. Though this hypothetical scenario would not reverse global warming nor bring temperatures back to pre-industrial levels, in small doses it may curb emissions and cut global temperature increases by as much as half. But it’s risky – some studies suggest that SG could cut back on precipitation in some parts of the world, furthering the risk of extreme climatic events such as hurricanes.  

“Some of the problems identified in earlier studies where solar geo-engineering offset all warming are examples of the old adage that the dose makes the poison,” said senior study author David Keith in a statement. “This study takes a big step towards using climate variables most relevant for human impacts and finds that no IPCC-defined region is made worse off in any of the major climate impact indicators. Big uncertainties remain, but climate models suggest that geoengineering could enable surprisingly uniform benefits.”

To see how SG might impact certain regions, researchers used high-resolution model predictions to simulate temperature and precipitation extremes, as well as rates of tropical storms. Publishing their work in Nature Climate Change, the team says that these unequal effects may be “overstated”. In fact, their models suggest that SG may cut future warming predictions by as much as half across the globe. Paired with predicted extreme rainfall and changes in water availability, more than 85 percent of increases in hurricanes could be offset. Altogether, less than 0.5 percent of land would see worsened climate conditions.

“The places where solar geoengineering exacerbates climate change were those that saw the least climate change to begin with,” said study author Peter Irvine. “Previous work had assumed that solar geoengineering would inevitably lead to winners and losers with some regions suffering greater harms; our work challenges this assumption. We find a large reduction in climate risk overall without significantly greater risks to any region.”

The authors note that their experiment is simplified, adding that it assumed double carbon dioxide concentrations in the future and representing SG by “turning down the Sun” under “idealized scenarios”. Halving warming isn’t necessarily optimal, but it is a good starting point for analyzing the effects of SG. A more modest approach could have better outcomes, they conclude. 

The UN is meeting this week to discuss new technologies like geoengineering to combat global warming. 

"How to understand and potentially harness disruptive new technologies for the benefit of all humanity is one of the defining questions of our age," former Secretary-General of the United Nations, Ban Ki-Moon, said in a statement. "Future generations will not forgive us if we fail to answer it convincingly."


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