More is getting written about a subject that as recently as a few years ago was as far away from mainstream thinking as, and barely more respectable than, the fantasies of science fiction. That subject is geoengineering—measures to ameliorate man-made climate change caused by greenhouse gases. A variety of possible techniques come under that label, including the sowing into the stratosphere of chemicals that would reflect more sunlight into space or the dispersal of other substances into the oceans to enable them to absorb more carbon dioxide. The increased attention results partly from scientific study of the subject, which has accelerated over just the last three or four years and has shown how application of some of the available technologies at a surprisingly modest scale could have significant effects on the global climate. It also results from the mounting evidence that human activity is indeed changing the global climate, reducing the ranks of the skeptics to die-hard deniers such as Senator James Inhofe (R-OK)--whose family, during one of last winter's snowstorms, built an igloo on the National Mall in Washington and labeled it “Al Gore's New Home”.

Geoengineering has its own skeptics. Some point out, quite correctly, that every time man has tinkered with nature, from containing rivers with levees to introducing non-native species as a way of controlling native pests, there have been unforeseen and unintended consequences. Some argue that the first priority regarding climate change is to reduce emissions of the greenhouse gases that are causing the problem in the first place, and that geoengineering would be a distraction from that task. Some are uncomfortable with the whole idea of intentional alteration of the climate, seeing it as playing God.

But mankind already is altering the climate; the issue is not whether to alter or not to alter, but instead what that alteration should encompass. Doing no geoengineering does not enable us to avoid a difficult and uncomfortable decision; it is itself a decision to limit the alteration to planet-warming greenhouse gas emissions (and countless other existing human-induced environmental effects, most of them undeniably negative) and not to employ existing technology that could modify the atmosphere in other ways.

As for the primary task of reducing emissions of the offending gases, geoengineering need not distract from that important goal. Instead it could complement it, by staving off the near-term danger of a catastrophic climatic tipping point (such as accelerated melting of ice in Greenland disrupting the North Atlantic currents that keep Western Europe temperate rather than frigid) while the longer term and more economically challenging task of reducing emissions proceeds. In short, geoengineering should be faced squarely and directly as a set of policy options, and it should be a major topic of debate and decision.

A big question is how that debate gets conducted and especially how the decisions should be made. So far most serious contemplation of such questions has been limited to a few unofficial players, including scientists who are addressing the technical issues. Unilateral decisions and actions by states clearly are insufficient for a topic that knows no international boundaries. An international regime for debate and decision about geoengineering is needed.

The closest the international community has come to this was at the most recent biennial review conference of the Convention on Biological Diversity, held last month in Nagoya, Japan. But the subject goes well beyond biological diversity, and decisions at the conference are not applicable to states not bound by the convention (the United States has not ratified the treaty). Moreover, the only decision taken at the conference was the negative one of imposing a de facto moratorium on geoengineering projects and experiments.

Decision-making on geoengineering will be a major international political challenge. Reaching agreement on any management and preservation of the global commons is difficult enough, as demonstrated by past deliberations on the law of the sea and—as far as greenhouse gas emissions are concerned—the Kyoto Protocol. Agreement on positive steps to alter intentionally an existing environmental pattern will be all the more difficult. It would be difficult even without clear conflicts of interest regarding the impact of such steps, given the irreducible uncertainties and risks involved.

The challenge is even greater because there are conflicts of interest between states concerning the effects of geoengineering and the problem it would be designed to correct. Global warming itself has differential impact. To some it means an intemperate local climate becoming even more intemperate, or the prospect of being inundated by rising sea water. To others it may mean a more moderate climate and increased agricultural opportunities. Moreover, successful geoengineering does not mean complete reversal of climate change and restoration of a status quo ante. Even if average global temperatures were stabilized at a level first reached decades ago, the combined effects of the greenhouse gases already emitted and the geoengineered responses to them would leave a different pattern, such as warmer polar regions and cooler equatorial ones. There could also be other effects such as reduced rainfall, which would be a major worry to some but of less concern to those already blessed with ample precipitation.

The political and governance issues associated with geoengineering need to be worked on to bring them up to speed with work on the technological issues. The sooner that work begins the better.