To save you the trouble of reading the fifth assessment report of the Intergovernmental Panel on Climate Change, John Upton over at Grist, has summarised it for you.
Read it here, What the IPCC found: The big news from the new climate assessment, and weep later.
Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased. IPCC, 27 September 2013
We need to change, and now.