The climate engineers

Emissions of carbon dioxide are rising even faster than was expected, and if they continue to do so we are on track for global temperatures which are likely to be 4C higher, or even more, by 2100, with disastrous consequences. With no action agreed by the recent G20 meeting, there is still no sign that we are even beginning to control emissions, let alone reduce them by the target of at least 50% by 2050, widely regarded as the minimum necessary to avoid that. Some people are therefore now suggesting that we should seriously consider geoengineering - that is, intervening directly to engineer the climate system, so as to moderate the rise of temperature. Is this possible? How? At a reasonable cost? Without undesirable side-effects? Who could do it? Who should control it?

It is to answer just these questions that the Royal Society has set up a study group on geoengineering climate. Without the answers there will be no way to take sensible decisions on this issue, based on evidence and facts rather than beliefs and suppositions (either for or against the idea). It may well be that our study will conclude that such schemes are not feasible, or too costly, have serious side-effects, or are too difficult to control. But it may not; and it is likely that we will need a lot more information before we can really decide.

Geoengineering is not an alternative to transforming our economies in order to achieve a low-carbon energy future; we will need that anyway, when the fossil fuels run out. But it is possible that it could at least make a contribution to reducing the damage which is otherwise expected. We would, in effect, at least be treating the symptoms, to buy some time while we seek a cure. But this will only be an option if we get the information to assess the credibility and potential of these ideas as soon as we can.

Geoengineering schemes for moderating climate change come in two main flavours. First there are those that aim to increase the amount of sunlight that is reflected away from the Earth (currently about 30%) by a few percent more. Second there are some that aim to increase the rate at which CO2 is removed from the atmosphere, by enhancing the natural sinks for CO2, and maybe even by deliberately scrubbing it out of the air.

It's pretty clear that some of the reflection schemes could successfully reduce temperatures, because that's just what happens after major volcanic eruptions. This method acts fast and the effects, like those of volcanoes, would decline after a few years, so it wouldn't be irreversible. This approach, however, would only be treating the symptoms, and could be used to allow even more CO2 to build up in the atmosphere. Then, if we were ever to stop enhancing the reflectivity, all that pent up global warming would happen very fast indeed, and we should be in serious trouble. This method also does nothing to moderate the "other CO2 problem", ocean acidification.

The CO2 removal schemes avoid these difficulties, since they attack the problem at its source; but they would only operate slowly, taking many decades to reduce CO2 to safer levels. They may not be able to achieve enough to make a real difference, and they may be very costly. And some CO2 reduction schemes, like ocean fertilisation, involve the large-scale manipulation of natural ecosystems, with effects that are very hard to predict.

It is no surprise that people's opinions on these ideas vary enormously; all the way from those who think we should get started right away, to those who think that we should not even consider them, let alone research them properly. The latter group say that simply doing the research may lead some people to believe that there may be a silver bullet for the climate problem after all, and if so they may reduce their efforts to get CO2 emissions under control. Such views are not unreasonable, and some of the schemes may have potential environmental impacts such that even the research needs to be internationally agreed and controlled. However, the Royal Society believes that decisions based on knowledge are better than those based on ignorance, and that public policy should be based on the best evidence we can get.

If world leaders are unable to agree on effective action to deal with climate change, and fail to implement practical measures to reduce CO2 emissions very soon, we may in future be glad that someone took these ideas seriously. Seriously enough to separate the real science from the science fiction, anyway. We intend that our study will be a useful contribution to doing just that.

John Shepeherd, deputy director of the Tyndall Centre for Climate Change Research at the University of Southampton, and Chair of the Royal Society study group on Geoengineering Climate.