since 1850 glaciers had been retreating but periods from 185o - present has had cooler TEMPERATURES which decreased that melting, but from 1980 to present a significant increase in TEMPERATUREs has led to glacier retreat increase rapidly, so much so that some glaciers have disappeared completely, and the existence of a great number of the remaining glaciers of the world is threatened. a good EXAMPLE of how much glaciers are threatened is at glacier national park, where glaciers may completely DISAPPEAR by 2100.