Few branches of science divide opinion as sharply as that championed by Professor David Keith.
He is one of the pre-eminent geo-engineers striving to find new ways to combat global warming, by altering the way the sea, the clouds and the atmosphere work.
This isn't a replacement, he says, for the political drive to reduce emissions. Tim Franks spoke to him about whether geo-engineering is a cost-effective, emergency stop-gap, before the effects of climate change become irreversible - or a dangerous leap into the unknown?
You can watch the full interview on BBC World News on Monday 14 November at 0430, 0930, 1530 and 2130 GMT and on BBC News Channel on Monday, 14th November 2011 at 0430 GMT and on Tuesday, 15th November 2011 at 0030 GMT.
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