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Researchers warn against abrupt stop to geoengineering method

As a range of climate change mitigation scenarios are discussed, University of Washington researchers have found that the injection of sulfate particles into the atmosphere to reflect sunlight and curb the effects of global warming could pose a severe threat if not maintained indefinitely and supported by strict reductions in greenhouse gas (GHG) emissions.

The new study, published today, 18 February, in IOP Publishing's journal Environmental Research Letters, has highlighted the risks of large and spatially expansive temperature increases if solar radiation management (SRM) is abruptly stopped once it has been implemented.

SRM is a proposed method of geoengineering whereby tiny sulfate-based aerosols are released into the upper atmosphere to reflect sunlight and cool the planet. The technique has been shown to be economically and technically feasible; however, its efficacy depends on its continued maintenance, without interruption from technical faults, global cooperation breakdown or funding running dry.

According to the study, global temperature increases could more than double if SRM is implemented for a multi-decadal period of time and then suddenly stopped, in relation to the temperature increases expected if SRM was not implemented at all.

The researchers used a global climate model to show that if an extreme emissions pathway—RCP8.5—is followed up until 2035, allowing temperatures to rise 1°C above the 1970–1999 mean, and then SRM is implemented for 25 years and suddenly stopped, global temperatures could increase by 4°C in the following decades.

This rate of increase, caused by the build-up of background greenhouse gas emissions, would be well beyond the bounds experienced in the last century and more than double the 2°C temperature increase that would occur in the same timeframe if SRM had not been implemented.

On a regional and seasonal scale, the temperature changes would be largest in an absolute sense in winter over high latitude land, but compared to historical fluctuations, temperature changes would be largest in the tropics in summertime, where there is usually very little variation.

Lead author of the research, Kelly McCusker, from the University of Washington, said: "According to our simulations, tropical regions like South Asia and Sub-Saharan Africa are hit particularly hard, the very same regions that are home to many of the world's most food insecure populations. The potential temperature changes also pose a severe threat to biodiversity."

Furthermore, the researchers used a simple climate model to study a variety of plausible greenhouse gas scenarios and SRM termination years over the 21st century. They showed that climate sensitivity—a measure of how much the climate will warm in response to the greenhouse effect—had a lesser impact on the rate of temperature changes.

Instead, they found that the rates of temperature change were determined by the amount of GHG emissions and the duration of time that SRM is deployed.

"The primary control over the magnitude of the large temperature increases after an SRM shutoff is the background greenhouse gas concentrations. Thus, the greater the future emissions of greenhouse gases, the larger the temperature increases would be, and, similarly, the later the termination occurs while GHG emissions continue, the larger the temperature increases," continued McCusker.

"The only way to avoid creating the risk of substantial temperature increases through SRM, therefore, is concurrent strong reductions of GHG emissions."

From Tuesday 18 February, this paper can be downloaded from

Notes to Editors


1. For further information, a full draft of the journal paper or contact with one of the researchers, contact IOP Press Officer, Michael Bishop: Tel: 0117 930 1032 E-mail: For more information on how to use the embargoed material above, please refer to our embargo policy.
IOP Publishing Journalist Area

2. The IOP Publishing Journalist Area gives journalists access to embargoed press releases, advanced copies of papers, supplementary images and videos. In addition to this, a weekly news digest is uploaded into the Journalist Area every Friday, highlighting a selection of newsworthy papers set to be published in the following week. Login details also give free access to IOPscience, IOP Publishing's journal platform. To apply for a free subscription to this service, please email Michael Bishop, IOP Press Officer,, with your name, organisation, address and a preferred username.
Rapid and extensive warming following cessation of solar radiation management

3. The published version of the paper 'Rapid and extensive warming following cessation of solar radiation management' (Kelly E McCusker et al 2014 Environ. Res. Lett. 9 024005) will be freely available online from Tuesday 18 February. It will be available at
Environmental Research Letters

4. Environmental Research Letters is an open access journal that covers all of environmental science, providing a coherent and integrated approach including research articles, perspectives and editorials.
IOP Publishing

5. IOP Publishing provides a range of journals, magazines, websites and services that enable researchers and research organisations to reach the widest possible audience for their research. We combine the culture of a learned society with global reach and highly efficient and effective publishing systems and processes. With offices in the UK, US, Germany, China and Japan, and staff in many other locations including Mexico and Russia, we serve researchers in the physical and related sciences in all parts of the world. IOP Publishing is a wholly owned subsidiary of the Institute of Physics. The Institute is a leading scientific society promoting physics and bringing physicists together for the benefit of all. Any profits generated by IOP Publishing are used by the Institute to support science and scientists in both the developed and developing world. Go to
Access to Research

6. Access to Research is an initiative through which the UK public can gain free, walk-in access to a wide range of academic articles and research at their local library. This article is freely available through this initiative. For more information, go to
The Institute of Physics

6. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application. We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.

Michael Bishop | EurekAlert!
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