Can climate engineering buy us time?

Engineering the earth’s climate: Can We? Should We?

Mike Hulme is professor of climate and culture at King’s College London, lives in Norwich.

This article first appeared in the 2015 May-June issue of The Magazine of the Diocese of Norwich.

Is it possible for humans to deliberately re-engineer the world’s climate? And if it is, are the hazards of global warming severe enough to justify such an ambition? Over the last 10 years the argument has been made by some scientists and environmental advocates that the world needs a radical technological fix for climate change. The prospect of such technologies being developed and maybe eventually used raises many important environmental, political and ethical questions.

Climate intervention technologies aim to do one of two things: either accelerate the removal of carbon dioxide from the atmosphere or else reflect more sunlight back into space (so-called Sunlight Reflection Methods; SRM). In this article I focus on the latter. By reducing incoming solar radiation, SRM technologies seek to offset global heating caused by rising greenhouse gas concentrations. They would achieve this by reflecting more sunlight back into space. These technologies include placing mirrors in near-Earth space orbit, whitening low-level marine clouds by spraying seawater into them and injecting tiny sunlight-reflecting particles (aerosols) into the stratosphere. This latter idea is called stratospheric aerosol injection (SAI) and has received the greatest attention.

Sunlight Reflection Diagram: © Durham UniversitySunlight reflection diagram

There are a number of reasons for this. By mimicking large volcanic eruptions many see SAI as a relatively simple – and a quite natural – technology. It is also fast-acting. Within months of beginning aerosol injections, a reduction in the averaged surface air temperature would probably become detectable. Many also see it as relatively cheap. Initial estimates suggest that SAI would be a fraction of the cost of substantially reducing global greenhouse gas emissions. Others argue that it is a technology that might ‘buy us time’. For example it might be justified if it were to give the world longer to transition to a zero-carbon energy economy.

However SAI is also a risky technology. There is no miniature Earth upon which to safely test SAI and computer simulation models are far from accurate or precise enough to determine what the risks might be and who will be exposed to them. The side-effects of SAI cannot be discovered without large-scale experimental research, but to do the research may cause the very side-effects which are to be avoided. For many, the range, extent and legacy of the possible risks associated with SAI would prohibit even research into technology, let alone its deployment.

Because SAI technologies aim to deliberately engineer a new global temperature (a bit like creating a thermostat for the planet), their prospect also raises a more troubling question: ‘Who should decide whether or not to implement the technology, when to do so, and what the thermostat setting should be?’ Many political scientists believe that just asking these questions of the world’s governments would heighten geopolitical tensions or even provoke new conflicts between nations.

Whether to deliberately engineer the world’s climate in this way is a question which impinges on the future of all life on Earth, today and in the future. The unintended outcomes of creating a thermostat in the sky would place an almost unbearable ethical responsibility upon those who might finally have to take the decision about whether or not to implement it.


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