The UN Intergovernmental Panel on Climate Change (IPCC) has published the 1st of 3 volumes of its fifth Assessment Report. The Summary for Policymakers, published Friday 27 September is here: http://www.climatechange2013.org/images/uploads/WGIAR5-SPM_Approved27Sep2013.pdf
The report is clear – warming of the climate system is unequivocal; since the 1950s, many of the observed changes are unprecedented over decades to millennia; the atmosphere and ocean have warmed, amounts of snow and ice have diminished, sea level has risen, and concentrations of greenhouse gases have increased. Each of the last 3 decades have been successively warmer at the earth’s surface than any preceding decade since 1850. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. Limiting climate change will require substantial and sustained reductions in greenhouse gases.