One of the clearest studies that the planet is warming

http://www.pbs.org/newshour/bb/science/july-dec12/hansen_08-06.html

PS.  P.B. sent me this:

Arctic summer ice has lost 3/4 of its volume in the last 3 decades, and if the trend continues we will have ice-free summer days within a decade or less.  The open waters will absorb additional energy.  Jet streams may be disrupted.  Vast amounts of methane may be released.  See: http://www.bbc.co.uk/news/science-environment-19496674

Also in the last 3 decades, the percentage of earths surface experiencing unusually hot summer temperatures has gone from .14 percent to 10 percent.  We are currently at the knee of the curve on this trend and the next leg of the journey will quickly take us from 10 percent to 50 percent (a simple extrapolation of the published results)  See: http://www.pnas.org/content/early/2012/07/30/1205276109.full.pdf+html