When I first heard of geoengineering as a serious response to climate change my response was deep scepticism. It seemed to me to be utter folly to attempt to address the problem of human influence on the climate system with some kind of counterbalancing intervention. This is what geoengineering by solar radiation management (SRM) attempts to do. I didn't like it. And yet here I am, a year and a half into a PhD project examining the effects on the atmosphere of SRM using stratospheric aerosols. How did this come about?

My interest in climate science stems from two quite distinct sources. One of these is a love for the scientific method as a way of understanding the world, in all its beauty and complexity. The other is concern for how humans can manage their existence sustainably. I see this as a form of environmentalism which recognises the extraordinary impact we have on the planet's natural systems. As humans spread and dominate this planet, we must recognise the burden we place on its resources and learn to manage our impact sustainably. For me this includes maintaining parts of this planet untouched by humanity, for I believe they have intrinsic value. Now, we may all have different opinions on the intrinsic value of Nature, but there can be no disagreement that we are pushing this planet's capacity to support us to its limits.

Here is the root of my concern about climate change. It represents our shift from a species in awe of the planet's systems to one actively influencing them. In a sense this idea is nothing new. We already manage environments on a small scale. In the UK we think of going 'back to nature' as going to the countryside. We feel at peace among patchwork fields of monoculture crops as if we are communing with Nature, but this landscape is as much a product of the human mind as the city. Thus we are no strangers to environmental management, but geoengineering requires that we move to planetary management. This is a big step, and not a direct extension of our previous efforts. Our track record on interventions in natural systems does not inspire confidence. We only need to look at the many cases of species introduced by humans destroying native ecosystems to see examples of this. This argument is at the heart of my concerns about SRM. I worry about how we can achieve sustainability when we are considering planetary management. If humans manage the climate system there is a serious risk it could go wrong. Human folly, just like human ingenuity, cannot be underestimated.

However, many of my concerns about geoengineering are the same as my concerns about unmitigated climate change: that human interventions in the climate system could damage the sustainability of human societies and the intrinsic value of our natural ecosystems. It is possible that the risk of climate change may in some future be so great it outweighs the risk of geoengineering by SRM.

In such a situation it would seem wise to consider carefully and research every option open to us. We may discover stratospheric SRM is a viable option, subject to ethical considerations (which, admittedly, may never be satisfied). We may find there are side-effects which make it unacceptable. Either way, I would rather research it and know the 'nature of the beast'.

This line of argument forces one to consider some uncomfortable questions. There must exist some situation in which I think deployment of SRM is desirable. And yet the conditions do not simply depend on the climate - it also depends on what we know about stratospheric SRM (i.e. what are the risks and benefits?). Thus it follows that we must know about this option so that we may decide on the conditions which make deployment acceptable. These requirements are scientific, ethical and political, which is why we need an interdisciplinary research effort.

Such ideas can (and perhaps should) make us feel uncomfortable. We are forced to confront the substantial power we can wield over the Earth's systems, and the fact that this power can be destructive. This destruction could be wrought by climate change or by geoengineering. Whatever happens, we much not pretend we do not possess such power—instead, we must acknowledge it, which is the first step towards managing this power in the interests of both people and planet.