contribution of working group i to the fifth assessment report of the intergovernmental panel on climate change stocker tf d qin gk plattner m tignor sk allen j boschung a nauels y xia v bex and pm midgley eds cambridge university press cambridge united kingdom and new york ny usa plant photosynthesis is unable to compensate for such a huge c overload resulting in a considerable increase in c levels in the atmosphere and a heightened greenhouse effect