Are we sure that human CO2 emissions are causing Arctic ice to melt from the *bottom*?

An admission from the alarmists at the National Snow and Ice Data Center

The buoy data have indicated increased amounts of melt on the underside of the ice cover in recent years; bottom melt last year was particularly extreme.

...In recent days, the buoys have indicated sub-freezing temperatures with surface melt coming to an end; however, bottom melt will continue for at least two to three more weeks and the ice extent decline, while slowing, will also continue.

Regarding the credibility of the National Snow and Ice Data Center, see their laughable page entitled Accuracy of science in Gore's movie An Inconvenient Truth:

TED: I think An Inconvenient Truth does an excellent job of outlining the science behind global warming and the challenges society faces in the coming century because of it.
...
Where can I read more scientific reaction to the movie, especially about aspects of the science that you don’t cover here?

WALT: RealClimate.org, a non-profit, non-governmental site run by scientists, has a good entry on the movie. See http://www.realclimate.org/index.php?p=299.