Solar geoengineering: a ticking time bomb scenario?

A terrorist organisation has hidden a weapon of mass destruction in the city, and it is timed to detonate within a matter of hours. The city is too vast to employ an effective search and destroy strategy, but, luckily, one of the terrorists has been captured. However, the terrorist is not cooperating during interrogation, and will not reveal the location of the ticking time bomb. Thousands of lives are at stake, and time is running out. The desperate situation inevitably leads to the unthinkable question: should torture be used to extract the vital information?

The ‘ticking time bomb scenario’ is a thought experiment born of consequentialist ethics, in which the ‘lesser evil’ of torture is weighed up against the ‘greater evil’ of mass murder. In other words, the end would appear to justify the means. The very same logic is often employed as justification for considering various forms of ‘solar geoengineering’ – a controversial suite of fast-acting technology proposals for reflecting fractions of sunlight away from the Earth in order to moderate global warming. Perhaps the best-known example of this is stratospheric aerosol injection – a proposal to inject reflective sulphate particles into the stratosphere and cool the Earth (see Figure 1: a hose held aloft by a helium balloon, a possible delivery mechanism for stratospheric aerosol injection).

(Source: here)

Insufficient efforts to reduce greenhouse gas emissions have led a number of scientists, civil society groups and governments to weigh up the ‘lesser evil’ of manipulating the hospitability of the Earth’s climate against the ‘greater evil’ of impending climate change and its manifold risks to humans and the environment. In particular, this ‘greater evil’ has increasingly come to be characterised by the risk of passing ‘tipping points’ – critical thresholds at which large-scale components of the Earth system may change state. One such example of this is the possible disintegration of the West Antarctic Ice Sheet, which would raise global sea level by 5 metres (see Figure 2: the West Anarctic Ice Sheet: a possible tipping point in the Earth’s climate system). So the threat of passing climate tipping points comes to resemble a ticking time bomb; and solar geoengineering a ‘lesser evil’ action.

(Source: Nasa)

Whilst on the face of it few would resist an action that would prevent thousands of deaths, acting in the ticking time bomb scenario rests on two critical assumptions. The first is that we have credible information on the ‘bomb’ and its risks. Whilst we can characterise different Earth system components as candidates for ‘tipping’, great uncertainties surround their critical thresholds; their corresponding forcings; and the spatial and temporal distributions of their potential impacts. The second critical assumption is that we have credible information on the outcomes of the action proposed to ‘defuse’ the bomb. The would-be outcomes of the range of fundamentally different solar geoengineering proposals are far from certain. Whilst research into these outcomes has begun in earnest, many critical questions remain: how effective and how risky might they be, and for whom? What ethical and legal issues might they raise, and how might they be governed?

It is easy to jump into the debate about whether or not to deploy solar geoengineering proposals in the face of a ticking time bomb scenario. In fact there are at present no serious suggestions to deploy solar geoengineering in the foreseeable future, certainly not before we have credible accurateinformation about the possible side-effects. The central question in this dilemma is this: will we ever have information that is ‘accurate’ enough? Could we ever be certain of when a tipping point would be passed, or even if we had already passed one? And could we ever know how effective solar geoengineering proposals truly are before they are deployed at scale? Could we make known the as yet unknown side effects, or would there still be unknown unknowns?

Back in the interrogation room, the terrorist’s captors struggle with the ethics of the unknown as the minutes tick by. Unlike the unfolding terrorist plot, however, we would seem to have the luxury of more than merely a matter of hours to improve our knowledge and its credibility. The question for us is: how should we spend that time (perhaps years and decades)? Should we shrink from researching solar geoengineering in the face of seemingly irreducible uncertainty, and run the risk of being caught unprepared? Or should we undertake prudent and responsible research to improve our knowledge as best we can, just in case the bomb goes off?