The IPCC, in its wisdom, has decided to wade into another emerging controversy – this time over whether any form of ‘geoengineering’ might be acceptable to contain rising global temperatures. At a meeting in Peru last week, experts from all the working groups looked at the various ideas currently in circulation and how they might be treated in the upcoming Fifth Assessment Report.
The answer to any question often depends on the phrasing of the question itself, and for geoengineering it is no different. It seems perverse, in my view, to include – as the IPCC does – the removal of carbon dioxide from the atmosphere in the same basket as ‘solar radiation management’, which includes for example efforts to intentionally change the planet’s albedo by spraying sulphate aerosols into the stratosphere. By the former definition, you engage in geoengineering every time you plant a tree. Moreover, why not include the addition of CO2 to the atmosphere under the category of ‘geoengineering’? That would make us all geoengineers every time we start the car or switch on a light.
The irony is that such a use of the term would be technically quite correct: we do all take part in geoengineering on a daily basis, and not just by our collective effect on the planet’s carbon cycle. We have altered the nitrogen cycle by an even greater proportion, through the synthesis and use of nitrogenous fertilisers. One might also consider the anthropogenic transformation of the land surface to be geoengineering, of a very physical nature – in which case all the world’s farmers are also geoengineers. It is because we have made this enormous transformation that we can now be said to be living on a human engineered planet in a new geological era, the Anthropocene.
However, in the everyday sense of ‘geoengineering’ I think the discussion should be more limited, to planetary-scale artificial efforts to mitigate global warming. There are various of these in circulation, some more realistic than others. The addition of mirrors at the Lagrange point between the sun and the Earth would be prohibitively expensive – more so by far than simply getting rid of fossil fuel-combusting technologies and replacing them with zero-carbon ones. More realistic by far is ‘solar radiation management’ by the addition of sulphates to the upper atmosphere – what makes this one scary is that it would probably actually work, and be achievable at reasonable cost (0.5-2.5bn $ a year).
Some quite ambitious experiments are indeed already being proposed. Researchers in the rather hush-hush ‘SPICE’ project (Stratospheric Particle Injection for Climate Engineering) are apparently considering the feasibility of building a giant 1km-high chimney near their laboratory in Cambridge, but are nervous about the public reaction. (You can imagine the tabloid headlines as the boffins carry out their crazy James Bond-type experiment in the air.) Actually I am told that it will be more like a garden hose tethered to a helium balloon, and will only spray out water vapour, but I doubt that minor detail will trouble the tabloid hacks.
We know that sulphate aerosols injected into the stratosphere act to cool the troposphere below because the effect can be observed every time there is a big enough volcanic eruption. Temperatures dipped by several tenths of a degree following the Pinatubo eruption of 1991, for example. But the addition of aerosols does not simply cancel out warming. It makes sunlight more diffuse, which stimulates plant growth ($) through photosynthesis – in the years following large volcanic eruptions the growth rate of CO2 in the atmosphere tends to fall. It also tends to deplete ozone in the stratosphere, not directly but through stimulating the formation of ‘polar stratospheric clouds’ which are the main sites for ozone destruction in the polar springtimes.
Most seriously, perhaps, is that aerosol injection would also alter precipitation patterns ($). This would mean reduced evaporation and precipitation worldwide, with enhanced drying in the sub-tropics. So the price we might pay for a reduction in global warming would be reduced rainfall in some parts of the world. This effect on the hydrological cycle would produce winners and losers and probably makes the whole thing politically unfeasible – once someone (the UN?) is intentionally altering the planet’s temperature, every drought and harvest failure would be blamed on the geoengineers, despite the scientific challenges of pinning any single event on the aerosol injectors (which are, naturally, the same challenges we face in attributing specific events to climate change).
But there is a real issue here: the globe is already cooled by human-injected aerosols, perhaps by half a degree or more. These come from biomass burning, coal-fired power stations and suchlike, and are injected into the troposphere, where they cause health-threatening air pollution. As China and other polluted developing countries get richer, they will doubtless insist on cleaner air. So the current aerosol sunshade will certainly be removed in decades to come, boosting global warming still further. So why not shift the aerosols from the troposphere to the stratosphere, where no-one has to breathe them? I put this as a proposal to illustrate unwitting planetary management is no different from intentional planetary management – except for the politics.
So the problems of geoengineering come down most to governance. Human beings are already having a great deal of trouble – see my posts from UNFCCC meetings – deciding what we want the average temperature of this planet to be over the next century. The possibility of directly influencing the atmospheric sunshade introduces a new level of complexity. But it is an option which must be explored, even if only as an insurance policy in the event of some catastrophic climatic tipping point. So let the research continue – but let no-one be fooled – as Bjorn Lomborg recently was – that the ‘solar radiation management’ variant of geoengineering is an easy or cheap option as compared to boring everyday reduction in carbon emissions.