"Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations." IPCC 2007 Summary for Policymakers, pg 5.
"Although there remains uncertainty in many aspects of climate science, as in all science, over the past few years an overwhelming and well-founded acceptance has emerged, not only in the scientific community, but among the general public and in political arenas, that human activity, and in particular the burning of fossil fuels, is warming the planet. Far from the debate being over, with this awareness the discourse on climate change has largely moved from one of questioning the science to disputing what ought to be done about the problem." Sir John Houghton in Nature