They are the ultimate technological fixes: schemes that will span our planet and involve scientists in reshaping our world to save it from global warming. Yet only a few years ago, such projects - giant space mirrors, flotillas of artificial cloud makers and ocean fertilisation programmes - were dismissed as the stuff of science fiction.
'Geo-engineering is one of the types of thing that are worth investigating,'
'If we can generate 100 ideas, and 97 are bad and we land up with three good ones, then the whole thing will have been worthwhile.'
Chance of success: 3/5 Impact on marine life could count against the scheme.
Chance of success: 1/5 Risks of acid rain and ozone depletion will provoke opposition.
Chance of success: 1/5 Incredibly expensive.
Chance of success: 2/5 Will need major global commitment to succeed.
clipped from: observer.guardian.co.uk