There is no simpler answer to this question. It's like answering the Q, 'When will there be a cure for cancer?'. In the case of cancer there are many types/causes all requiring different approaches. In the case of GW, most people now agree that there is one major cause, anthropomorphic carbon dioxide emission. There are several technological approaches to this: nuclear power, solar energy, other 'alternative energy' supplies (wind power, wave energy,... carbon sequestering, etc etc. These will all help to reduce carbon dioxide emissions, but no single 'cure-all'. I am with the others who've said that there needs to be a reduction in global human population.
David Atenborough has just become patron of the 'Optimum Population Trust'.
BBC NEWS | UK | Attenborough warns on population
On BBC radio this morning he said something like,
'There is no major world problem that is not due to human overpopulation, and no major world problem that can't be ameliorated by reducing the human population'
A