It is quite likely that we will at some point see people starting to make deliberate changes in the way the climate system works. When they do they will change the world — though not necessarily, or only, in the way that they intend to.

"Geoengineering" technologies for counteracting some aspects of anthropogenic climate change — such as putting long-lived aerosols into the stratosphere, as volcanoes do, or changing the lifetimes and reflective properties of clouds — have to date been shunned by the majority of climate scientists, largely on the basis of the moral hazard involved: any sense that the risks of global warming can be taken care of by such technology weakens the case for reducing carbon-dioxide emissions.

I expect to see this unwillingness recede quite dramatically in the next few years, and not only because of the post-Lehman-Brothers bashing given to the idea that moral hazard is something to avoid at all costs. As people come to realise how little has actually been achieved so far on the emissions-reduction front, quite a few are going to start to freak out. Some of those who freak will have money to spend, and with money and the participation of a larger cadre of researchers, the science and engineering required for the serious assessment of various geoengineering schemes might be developed fairly quickly.

Why do I think those attempts will change the world? Geoengineering is not, after all, a panacea. It cannot precisely cancel out the effects of greenhouse gases, and it is likely to have knock on effects on the hydrological cycle which may well not be welcome. Even if the benefits outweigh the costs, the best-case outcome is unlikely to be more than a period of grace in which the most excessive temperature changes are held at bay. Reducing carbon-dioxide emissions will continue to be necessary. In part that is because of the problem of ocean acidification, and in part because a lower carbon-dioxide climate is vastly preferable to one that stays teetering on the brink of disaster for centuries, requiring constant tinkering to avoid teetering over into greenhouse hellishness.

So geoengineering would not "solve" climate change. Nor would it be an unprecedented human intervention into the earth system. It would be a massive thing to undertake, but hardly more momentous in absolute terms than our replacement of natural ecosystems with farmed ones; our commandeering of the nitrogen cycle; the wholesale havoc we have wrought on marine food webs; or the amplification of the greenhouse effect itself.

But what I see as world changing about this technology is not the extent to which it changes the world. It is that it does so on purpose. To live in a world subject to purposeful, planetwide change will not, I think, be quite the same as living in one being messed up by accident. Unless geoengineering fails catastrophically (which would be a pretty dramatic change in itself) the relationship between people and their environment will have changed profoundly. The line separating the natural from the artificial is itself an artifice, and one that changes with time. But this change, different in scale and not necessarily reversible, might finish off the idea of the natural as a place or time or condition that could ever be returned to. This would not be the "end of nature" — but it would be the end of a view of nature that has great power, and without which some would feel bereft. The clouds and the colours of the noon-time sky and of the setting sun will feel different if they have become, to some extent, a matter of choice.

And that choice is itself another aspect of the great change: Who chooses, and how? All climate change, whether intentional or not, has different outcomes for different regions, and geoengineering is in many ways just another form of climate change. So for some it will likely make the situation worse. If it does, does that constitute an act of war? An economic offence for which others will insist that reparations should be made? Just one of those things that the stronger do to the weaker?

Critics of geoengineering approaches are right to stress this governance problem. Where they tend to go wrong is in ignoring the fact that we already have a climate governance problem: the mechanisms currently in place to "avoid dangerous climate change", as the UN's Framework Convention on Climate Change puts it, have not so far delivered the goods. A system conceived with geoengineering in mind would need to be one that held countries to the consequences of their actions in new ways, and that might strengthen and broaden approaches to emissions reduction, too. But there will always be an asymmetry, and it is an important one. To do something about emissions a significant number of large economies will have to act in concert. Geoengineering can be unilateral. Any medium sized nation could try it.

In this, as in other ways, geoengineering issues look oddly like nuclear issues. There, too, a technological stance by a single nation can have global consequences. There, too, technology has reset the boundaries of the natural in ways that can provoke a visceral opposition. There, too, there is a discourse of transcendence and a tendency to hubris that need to be held in check. And there, too, the technology has brought with it dreams of new forms of governance. In the light of Trinity, Hiroshima and Nagasaki, many saw some sort of world government as a moral imperative, an historical necessity, or both. It turned out not to be, and the control of nuclear weapons and ambitions has remained an ad hoc thing, a mixture of treaties, deterrence, various suasions and occasional direct action that is unsatisfactory in many ways though not, as yet, a complete failure. A geoengineered world may end up governed in a similarly piecemeal way — and bring with it a similar open-ended risk of destabilisation, and even disaster.

The world has inertia and complexity. It changes, and it can be changed — but not always quickly, and not necessarily controllably, and not all at once. But within those constraints geoengineering will bring changes, and it will do so intentionally. And that intentional change in the relationship between people and planet might be the biggest change of all.