The Working Group I contribution to the IPCC Fourth Assessment Report describes progress in  understanding of the human and natural drivers of climate change, observed climate change, climate processes and attribution, and estimates of projected future climate change. It builds upon past IPCC assessments and incorporates new findings from the past six years of research.Key findings include:

warming of the climate system is unequivocal, as is evident from obervations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level
the annual carbon dioxide concentration growth rate, the global atmospheric concentration of methane, and the global atmospheric concrentration of nitrous oxide have all increased in the last ten years
eleven of the last twelve years (1995-2006) rank among the 12 warmest years in the instrumental record of global surface temperature since 1850
average arctic temperatures increased at almost twice the global average rate in the past 100 years
at continental, regional and ocean basin sclaes, numerous long-term changes in climate have been observed including changes in precipitation amounts, ocean salinity, wind patterns, and aspects of extreme weather such as droughts, heavy precipitation, heat waves ad the intensity of tropical cyclones
 paleoclimatic information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1,300 years
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
for the next two decades, a warming of about 0.2 degrees celcius per decade is projected for a range of SRES emission scenarios.