Generally the costs of reducing GHG emissions by saving energy are lower than by switching to alternative energy sources, in particular biofuels. (treehugger.com)
This indicates a pretty rapid response to a change in GHGs in the atmosphere. (theinconvenientskeptic.com)
But I do not think that the analysis can be used to exclude the possibility of a contribution of increased GHG forcing. (wattsupwiththat.com)