George Bird Grinnell, an influential author, became an early advocate of setting this area as a preserve after visits in the 1880s. He first explored the glacier that was to bear his name, Grinnell Glacier, in 1887 and described it as being 1000 feet high and several miles across. About 90% of the ice that Grinnell saw is now gone. It was about 151.3 acres as of 2006. Glaciologists have predicted that if carbon dioxide levels increase at a worst-case scenario, all the glaciers in the park, including Grinnell, will disappear by the year 2030.