I visited the Exit Glacier in Alaska last spring.
As you approached the foot of the glacier signs began to appear with dates. The earliest date was 1892 cor maybe 1894. This sign was a fairly long distance from the current end of the ice.
The point is that the US Government has been tracking the glacial retreat for more than 100 years and that if there is global warming, the process has been underway for a very long time.
http://www.springerlink.com/content/l15444p1335h5564/
Climatic conditions in the Alps in the years about the year of Hannibal’s crossing (218 BC)
excerpt:
By the 3rd century BC the Alpine glaciers were in a backward position compared with their position in 900-350 BC. This fact and the mildness of the climate, inferred from tree-ring analyses, suggest that ice conditions were not severe in the Alps in 218 BC.