Should climate be engineered? A social scientist, natural scientist discuss

The spectre of climate engineering hung heavily over the recent United Nations climate conference in Katowice, COP24.

Rob Bellamy: 2018 has been a year of unprecedented weather extremes around the world. From the hottest temperatures ever recorded in Japan to the largest wildfire in the history of California, the frequency and intensity of such events have been made much more likely by human-induced climate change. They form part of a longer-term trend – observed in the past and projected into the future – that may soon make nations desperate enough to consider engineering the world’s climate deliberately in order to counteract the risks of climate change.

Indeed, the spectre of climate engineering hung heavily over the recent United Nations climate conference in Katowice, COP24, having featured in several side events as negotiators agreed on how to implement the landmark 2015 Paris Agreement, but left many worried that it does not go far enough.

Matt Watson: Climate engineering – or geoengineering – is the purposeful intervention into the climate system to reduce the worst side effects of climate change. There are two broad types of engineering, greenhouse gas removal (GGR) and solar radiation management (or SRM). GGR focuses on removing anthropogenically emitted gases from the atmosphere, directly reducing the greenhouse effect. SRM, meanwhile, is the label given to a diverse mix of large-scale technology ideas for reflecting sunlight away from the Earth, thereby cooling it.

An engineered future?

RB: It’s increasingly looking like we may have to rely on a combination of such technologies in facing climate change. The authors of the recent IPCC report concluded that it is possible to limit global warming to no more than 1.5°C, but every single one of the pathways they envisaged that are consistent with this goal require the use of greenhouse gas removal, often on a vast scale. While these technologies vary in their levels of maturity, none are ready to be deployed yet – either for technical or social reasons or both.

If efforts to reduce greenhouse gas emissions by transitioning away from fossil fuels fail, or greenhouse gas removal technologies are not researched and deployed quickly enough, faster-acting SRM ideas may be needed to avoid so-called “climate emergencies”.

SRM ideas include installing mirrors in Earth’s orbit, growing crops that have been genetically modified to make them lighter, painting urban areas white, spraying clouds with salt to make them brighter, and paving mirrors over desert areas – all to reflect sunlight away. But by far the best known idea – and that which has, rightly or wrongly, received the most attention by natural and social scientists alike – is injecting reflective particles, such as sulphate aerosols, into the stratosphere, otherwise known as “stratospheric aerosol injection” or SAI.

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