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expert reaction to geoengineering for cooling and ozone protection

New research published in PNAS, reports that releasing an aerosol of calcium carbonate into the atmosphere would cool the air, without damaging the ozone layer.


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

“This works adds to a body of research looking at aerosol injection as a possible tool in the fight against climate change. This technique is sometimes referred to ‘sunscreen for the Earth’, as the aerosol particles cool the planet by reflecting sunlight back out into space. This paper focuses on a mechanism that, while achieving that primary aim, also has the effect of protecting ozone by mopping up acidic species in the stratosphere – what we might call ‘indigestion tablets for the sky’.

“Although both unpalatable and sub-optimal, I’m afraid the time has come to start looking at these techniques more seriously. Recent political events, especially those in the US, strongly indicate that we are becoming ever less likely to solve this problem through conventional mitigation alone. That therefore requires us to think about a range of potential solutions no matter how politically, socially or technologically challenging they may be.” 


Prof John Shepherd FRS, Emeritus Professor of Earth System Science at the University of Southampton, said:

“If we fail to curb CO2 emissions enough, we may sometime need to deploy scary remedies like solar geoengineering (reflecting a few percent of sunlight back into space). The obvious method for this would be to try to mimic volcanoes, and inject sulphate aerosol into the stratosphere.

“However, such particles would be expected to react with ozone, and so deepen the ozone hole. David Keith and colleagues propose an alternative, the use of calcium carbonate (chalk) particles, which should be free of that unfortunate side effect, and work well enough. If we do ever need to use such technology, we should try to find a technique with few damaging side effects, so this research is welcome, even if we hope that we never need to use it.”


Dr Hugh Hunt, Reader in Engineering Dynamics and Vibration at the University of Cambridge, said:

“The proposal to use solid aerosol particles for SRM has many advantages.  One not mentioned is that small-scale low-concentration experiments can be carried out in a way that is impossible with sulphate injection as it takes days for a stable aerosol to form.  Such experiments are now urgently required because techniques for delivery and dispersion of particles, especially to avoid agglomeration, are difficult to model.  The longevity of solid aerosol particles needs to be measured in-situ.  It is likely that SRM will become an integral part of a combined policy to reduce climate risks and to meet the 1.5-degree target mark agreed at COP21 in Paris.  All the more reason to get moving with low-impact experiments in the stratosphere.”


* ‘Stratospheric solar geoengineering without ozone loss’ by David W. Keith et al. will be published in PNAS at 8pm UK TIME on Monday 12 December, which is also when the embargo will lift. 


Declared interests

Prof Shepherd was chair of the Royal Society 2009 study on Geoengineering, and co-chair of SRMGI, the Solar Radiation Management Governance Initiative.

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