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expert reaction to study of stratospheric aerosol injection

Researchers publishing in Environmental Research Letters have reviewed the capability and cost of delivering sulphates into the lower stratosphere as part of a solar geoengineering project. 


Dr Matthew Watson, Reader in Natural Hazards at the University of Bristol, said:

“This paper revisits the question of how much technologies that might combat global warming directly would cost. The focus is on the idea that it is possible to reduce global temperatures by injecting material that scatters sunlight away from the Earth, a process that is seen after large volcanic eruptions.

“Climate engineering, and in particular this type of climate engineering, is controversial. Unfortunately, climate change is dire enough for us to have to consider drastic action. Some argue against researching these ideas but personally I think that is a mistake. There may come a time, in a future not so far away, where it would immoral not to intervene. Given that, we are beholden to at least think about these ideas. Personally, I find the cost of the technologies the least interesting part of the problem, but the research still needs to be done there too.”


Dr Phil Williamson, Honorary Reader, University of East Anglia

“The new study shows that adding aerosols to the upper atmosphere to cool the planet is not as easy as had been thought.  New aircraft would need to be designed and built to spray sufficient sulphate into the stratosphere to achieve the desired effects.

“The cost is estimated to be a few billion US dollars per year, considered to be ‘relatively inexpensive’.  However, there is another, higher cost that is much harder to estimate: the pay-out that would be necessary to recompense nations who continued to experience extreme climate events, and who would then consider that solar geoengineering had been responsible.

“Politically, such scenarios are fraught with problems – and international agreement to go ahead with such action would seem near-impossible to achieve.  Rapid reductions in emissions remains the best way to avoid climate catastrophe.”


Prof Joanna Haigh FRS, Professor of Atmospheric Physics and Co-Director of the Grantham Institute for Climate Change and Environment, said:

 “In just 12 years the world needs to have invested its efforts into peaking greenhouse gas emissions to avoid crossing the 1.5 degree threshold seen as the danger point by the IPCC. Why then set out a plan to implement solar radiation management (SRM) from a date 15 years hence? This plan is a distraction that may well encourage weaker action on emissions reduction by governments in the hope they will no longer be necessary.

“Previously proponents of SRM have suggested that it be used to delay the onset of the inevitable warming arising from human greenhouse gas emissions. This paper, however, seems to suggest that the implementation should be ongoing. Forever? And it avoids any discussion of the well-documented side effects of sulphate geoengineering, including changes to weather patterns and ocean acidification by the unremitting CO2.

“The paper further insists that the SRM implementation is cheap compared, say, with national defence spending. I suggest that, alternatively, $5bn per year would make a welcome contribution to addressing the pressing mitigation and adaptation needs of developing countries, thereby also improving their economic conditions and stability.”


Prof Peter Cox, Professor of Climate System Dynamics at the University of Exeter, said: 

“This study looks at the cost and feasibility of injecting bright particles into the stratosphere, as a fast way to counteract global warming from greenhouse gases”.

“We are pretty sure that this would work to cool global temperatures, because it is essentially how volcanic eruptions cool the climate. It would not save us from other aspects of climate change like shifts in rainfall patterns”.

“The fact that researchers at one of the world’s top universities are costing the deployment of such a radical scheme shows how urgent the climate change problem has become”.    


‘Stratospheric aerosol injection tactics and costs in the first 15 years of deployment’ by Wake Smith and Gernot Wagner et al. was published in Environmental Research Letters at 00.00 GMT on Friday 23 November 2018. 


Declared interests

Dr Williamson “is employed by UK Research & Innovation as Science Coordinator for the Greenhouse Gas Removal research programme.  His comments are given in a personal capacity.”

Prof Haigh: “No conflict of interest.”

Dr Watson: “No conflicts.”

No others received.

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