The annual rate of growth in emission since the turn of the century (2.5%) has eclipsed the 0.9% annual increase observed across the 1990s. The co-chair of the Global Carbon Project, Dr Mike Raupach, reported last week that about 8 billion tonnes of carbon were released to the atmosphere globally in 2005.

Meanwhile, as flood succeeds drought as Kenya’s chief climatic curse, the second meeting of parties to the Kyoto protocol has recently ended in Nairobi, with no further decisions made about post-Kyoto emissions reduction targets – just a decision to hold further discussions in 2008. The absurd political logjam remains.

A few months back, one of atmospheric science’s most eminent practitioners, Paul Crutzen – who won the 1995 Nobel chemistry prize for his work on stratospheric ozone depletion – published a startling article in the journal Climatic Change. Citing the ‘grossly unsuccessful’ international response to global warming, Crutzen floated the possibility of injecting massive amounts of sulphur dioxide (SO2) into the atmosphere (via balloon-mounted artillery guns, no less) to counteract warming.

SO2 aids the development of clouds that reflect solar radiation, and anthropogenic SO2 emissions in the recent past have thus partially countered warming associated with greenhouse gas emissions. But deposition of sulphates also carries negative human and ecological consequences – the WHO estimates that such pollutants cause 500,000 premature deaths worldwide each year.

In contrast to GHG emissions, the world has been relatively successful in reducing SO2 emissions (at a rate of 2.7% per year in recent decades to its current value of less than 60 million tonnes). But this reduction is thought to have been partially responsible for increases in warming rates since the 1970s, and modelling estimates suggest that total cessation of SO2 emissions could lead to further rises of more than 1oC.

So what amounts would be required to counteract warming? There is, to some extent, a natural precedent for this – the 1991 Mt. Pinatubo eruption injected around ten million tonnes of sulphur into the atmosphere and caused a global surface temperature drop of around 0.5oC in the year following. But the atmospheric residence time of sulphates is short – modelling suggests that something on the order of Mt Pinatubo would be required every two years to offset mid-range warming rates.

Crutzen argues that he’s not in favour of SO2 injection, but that given current trajectories (global emissions remain close to the IPCC ‘business as usual’ curve) it may require consideration as a last ditch alternative. His hope is that discussion of such drastic steps might startle policy makers into effective action. Nairobi must have given him pause on that front.

An idea like this is difficult to quarantine once it reaches the public domain. The very same interests that obstruct effective negotiation of global emission reductions are likely to nominate such technological treatment of symptom over cause as an appropriate answer to our problems. The self-appointed hard-headed realists might argue that attempts to reign in GHG emissions have failed, and that we must inevitably (they like that word) turn to such ‘solutions’.

But the complexity of the climate system means that it is a highly uncertain one that, even if it ‘works’ may create at least as many problems as it solves – leaving policymakers to practice a sort of atmospheric triage where the death and destruction associated with climate change is weighed against that from sulphate deposition. And it could be argued that it is precisely this interventionist technological hubris that created the problems we’re already confronting. Can more really get us out of it?

Peter Fray

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