If human activity is causing the globe to warm in 2012, what caused it to do the same way back in the 1930's?
See "1930s photos show Greenland glaciers retreating faster than today, but nobody thought it was a big deal."
The reason nobody thought it was a big deal back then is because scientists in the 30's didn't have all those sophisticated surface, troposphere, and stratosphere data gathering, measuring, and modeling instruments. Nor did they have intergovernmental bodies to coordinate the study of climate. Nor a cohesive (pedantic) academy. Nor the IQ.
And they didn't have Al Gore to make silly movies about inconvenient truths.
So the globe warmed in the 30's, glaciers melted, and nobody soiled his undies in fear of planetary catastrophe.
How much more sophisticated we are today.