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BBC News
It's the stuff of science fiction, but could mirrors in space or sea water sprayed in the air be shortcuts to halt global warming?
"It's Dr Strangelove.
But it's the kind of Dr Strangelove you could see governments really using."
That's how one expert describes geo-engineering - the idea that we can use a kind of technical quick fix to cool the planet if global warming accelerates.
Plans for geo-engineering can sound bizarre.
They range from placing millions of tiny mirrors in space to reflect back some of the sun's rays, to using rockets to launch tons of sulphur into the stratosphere to create a kind of planetary sun shade.
That plan was inspired by watching what happened after the eruption of the Mount Pinatubo volcano in the Philippines in 1991.
Sulphur ejected into the atmosphere spread around in subsequent months to create a layer believed to have had a temporary cooling effect as it blocked some of the sun's warmth.
Other suggestions include spraying sea water into the atmosphere to make it cloudier, or pumping carbon dioxide out of the atmosphere or out of the oceans.
Until recently, policymakers have dismissed this as science fiction, a complete distraction from the fight against global warming. Now, attitudes seem to be changing.
"I think we're faced with such an enormous problem that we need to do all the research we can to see if there are any geo-engineering proposals which work through to the marketplace," says Professor Sir David King, until recently the government's chief scientific adviser.
There are still many scientific doubts about geo-engineering. What might the side effects be? Are such schemes irreversible?
Plan B
But as there is now so much pessimism about whether governments will ever agree to reduce carbon emissions enough, more and more scientists say we need to know exactly what our other options are.
If we don't do any research, says Professor Brian Launder of Manchester University, who is editing a new study of geo-engineering for the Royal Society, "we won't have anything that we can bring into place in 2030 say, when suddenly the world is at a crisis point".
Some forms of geo-engineering are also surprisingly cheap. That leads to fears that governments facing particular climatic problems might go it alone.
China and India, which have growing scientific capabilities, could use geo-engineering as a way of challenging international climate policy if they saw it as too skewed towards the interests of Western countries.
Or, even more alarmingly, an individual might decide to play with the global climate.
Professor David Victor, of Stanford University, imagines a scenario in which someone is frustrated at the lack of international action. "[They] could buy the aircraft and buy the rockets and just start doing some geo-engineering off their own island."
James Bond films of the future, he adds, might not feature Goldfinger. It could be Greenfinger, hand hovering over the global thermostat.
Running on empty
So how can geo-engineering be policed? It's a major challenge.
While climate change treaties try to persuade everyone to do the same things and reduce emissions, agreements on geo-engineering would be about stopping something happening - something we don't yet understand.
But Sir David King says we should at least begin to discuss it as part, and still a minor part, of the climate change policy debate.
"We need to make sure that there is control and validation over any of these procedures. But at the same time let's not take attention away from the major issue of removing our dependence on fossil fuels."
The dilemma is painful. Discuss a technical fix for future climate change, and people assume there's less need to cut carbon emissions now. Ignore it, and possibly face a kind of climate anarchy.
Others suggest geo-engineering should be embraced with enthusiasm, such as Julian Morris, of International Policy Network, a think tank sceptical about climate change and in favour of free market solutions.
"Investments in geo-engineering research are almost certainly the biggest bang for the buck that one could get in terms of addressing catastrophic climate change - a much, much bigger return than, for example, trying to control carbon emissions at the moment," he says.
"In fact diverting money into controlling carbon emissions and away from geo-engineering is probably morally irresponsible."
Most scientists and governments say geo-engineering remains hazardous and is only a partial fix. And they hope it will never be needed. But if global warming becomes more and more threatening, some will see it as the lesser risk.
Professor Scott Barrett, of Johns Hopkins University in Baltimore and an expert on international environmental agreements, says he ignored geo-engineering for many years.
Now, faced with the failure to reduce emissions enough, he says there are no easy options.
"[Geo-engineering] is not something we're going to want to use as a first choice. I think the chances are likely that it will eventually be used, for better or worse, in circumstances in which the risks of not using it seem to be higher than the risks of using it."
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(BBC)
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