Why We Should Not Engineer A Global Thermostat

By Mike Hulme

Can science fix climate change? A case against climate engineering

The Climate Engineering Conference in Berlin this August is providing a venue to debate in as open as way as possible the political, scientific, economic, ethical and cultural implications of this wide array of technologies. This is important to do because the consequences of implementing some of these technologies are wide-ranging and decisions should not be made by default or without public scrutiny.  In my recently published book ‘Can Science Fix Climate Change?  A Case Against Climate Engineering, I critique one specific climate engineering proposal, namely to deliberately introduce sulphate aerosols into the stratosphere to regulate global temperature.

My argument is that the putative technology of stratospheric aerosol injection (SAI) offers a triple fantasy: first, that the risks of a changing climate can be defused effectively by regulating global temperature; second, that the world could ever agree on the level at which to set the thermostat; and, third, that the unintended consequences of such intervention are manageable.  Creating a global thermostat as a response to climate change is an inadequate solution to a wrongly framed problem.


There is an inherent flaw in the operationalizing of SAI technology that makes its pursuit deeply undesirable.  The imagined thermostat works through agents who decide, on the basis of some scientific calculus of predicted dose and response, exactly how much aerosol to inject, where and for how long. These decisions are therefore informed by planetary-scale calculations of global temperature and global radiation balance.  The justification for implementing them – the only justification – is to regulate, maybe to stabilise, global temperature on the grounds of avoiding or defusing a climate emergency (in my talk at the CEC14 in Berlin on 20 August I shall be scrutinising what is meant by a ‘climate emergency’).

But the supposed benefits of such an intervention cannot be simply indexed against either of these two global variables: temperature or the radiation balance.  The welfare, in relation to weather and climate, of humans and of the things that matter to them cannot be reduced to such a calculus.  It too easily suggests the problematic notion of a global ‘we’, one that collapses valid and competing interests into a unitary global subject.  A stable global climate does not equate to stable local climates; achieving the former does not guarantee achieving the latter.


A planetary thermostat in the stratosphere would be ungovernable. Deciding when to implement it and agreeing what the setting should be and how it should be governed in the imaginable future would demand an unprecedented – and simply unattainable – degree of trust and cooperation among the nations of the world.  The alternative governance scenarios of voluntary coalitions of interested actors or unilaterally implementing political entities are unlikely to be sustainable and will lead to political rancour and possibly to military conflict.

This problem of how SAI technology would be governed undermines not just arguments for its deployment at some point in the future.  It also undermines the case for undertaking research today into the technology and its consequences. It is not an appropriate response to claim that ‘we’ need better to understand the technology in case ‘we’ should need to deploy it in the future.  Agreeing on conditions of deployment demands that expression be given to the multitude of perspectives and arguments about why a particular climate condition might or might not be deemed a universal emergency.  Different interests must be given voice and recognition – from both powerful and powerless nations, from Indigenous peoples, from people of faith and of no faith, and they must be ventriloquized for those who are not yet born, to give consideration to their interests.


Intentions matter in the consideration of ethics.  Through the transformation of land, the production of energy, the consumption of materials, and the begetting of children humans have altered the physical processes of climate around the world.  And we have been doing so for a very long time, certainly for a thousand years, maybe for ten thousand.  The experimentation with climate that has resulted from these activities has been inadvertent and unintentional. But to deliberately change the condition of the planet’s atmosphere in order to compensate for an induced planetary heating, is an entirely different form of experimentation.  It is intentional intervention.  It suggests a supreme confidence in human knowledge and ingenuity – a confidence approaching arrogance.

Some experiments are unavoidable; and some experiments are worth conducting.  But all experiments that fall into these categories are limited in scale and scope.  And experiments are entered upon because the outcome is not known.  Will patients recover after receiving a new drug? Do crops grow faster after the application of a new fertiliser?  Will this new material conduct electricity efficiently? Absurdly, the experiment with SAI would have to be justified on the (false) grounds that the outcome is already known, that it will deliver the desired ‘beneficial’ outcome, that a global thermostat can stabilise the climate.  But there are limits to human knowledge; our species is a product of evolution, not its author or controller.


Aldous Huxley’s 1932 novel Brave New World can be understood as portraying either a too perfectly controlled utopia or a brutal and inhuman dystopia.  It offers a way of imagining the consequences of seeking to perfect humanity through ever increasing technological intrusions. But in this brave new world human enhancement comes at a terrible cost.  I compare Huxley’s tale with the vision behind the technology of SAI and other global sunlight reflection methods.  These thermostat visionaries are seeking to enhance the world’s climate in the name of a noble cause.  They offer technologies that will not just compensate for a disturbed global heat balance; they will end up doing far more.  They will inaugurate an era of never ending experimentation with the global sky.  In their search for ever more control and adjustment, they will convert the world’s climate – all our climates – into something relentlessly unnatural.  SAI will usher in a brave new world of designer climates.

There is a form of experimentation that is both inevitable and desirable for humans, given their insatiable curiosity and appetite for creativity.  But, since we are inescapably enlisted on the project of remaking the world, I would rather do so slowly, humbly and, yes, accidentally. Let us attend to the difficult pursuit of liberty, justice and human security on the ground and not delude ourselves that utopias can be engineered in the sky.

See also the WIREs Climate Change virtual special issue on ‘Engineering Global Climate