There aren't a lot of people in the scientific community denying it:
http://iopscience.iop.org/1748-9326/8/2/024024
"We analyze the evolution of the scientific consensus on anthropogenic global warming (AGW) in the peer-reviewed scientific literature, examining 11,944 climate abstracts from 1991–2011 matching the topics 'global climate change' or 'global warming'. ... Among abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming. In a second phase of this study, we invited authors to rate their own papers. ... Among self-rated papers expressing a position on AGW, 97.2% endorsed the consensus. ... Our analysis indicates that the number of papers rejecting the consensus on AGW is a vanishingly small proportion of the published research."