Located near Juneau, Alaska, the Juneau Icefield is the fifth-largest icefield in North America. Straddling the US-Canadian border between Alaska and British Columbia, the 1,500-square mile icefield has over 30 major outlet glaciers, including the Llewyn Glacier near Atlin, BC and the Mendenhall Glacier and Taku Glacier near Juneau. The elevation the icefield ranges from about 3,500 feet at the edges to almost 6,000 feet in the central area near the Alaska-Canadian border. Although researchers are still not entirely certain, the current estimate is that the thickness of the ice sheets covering the area is somewhere between 4,500 and 5,000 feet, or perhaps even thicker in places.

The Juneau Icefields are most likely a remnant of the Great Ice Age of circa 25,000 to 12,000 BC, during which the greater part of North America was covered under a sheet of ice. Even during Cavell Advance of the around 1200 to 1850 AD, a much greater percentage of the land in Southeast Alaska was covered by icefields than is currently the case. It is icefields such as these that have been primarily responsible for the formation of Southeast Alaska's extensive networks of mountains and fjords.

Until about 1950, the Juneau Icefield was virtually unknown: very few (if any) expeditions had set foot on the icefield, and (partly as a result of this) maps of the icefield were highly innacurate. However, at the height of the Cold War in the early 1950s, the US government began a research organisation called the Juneau Icefield Research Program (JIRP) to study the feasability of building nuclear missile facilities on the icefield. JIRP began by making an extensive survey of the icefield, the data of which even modern maps of the icefield are based upon. When the Cold War cooled down and the nuclear missile plans were scrapped, JIRP continued under the direction of Dr. Maynard Miller, with a new mission aimed wholly at scientific research. It was JIRP that was likely one of the first organisations to hypothesise global warming; and this hypothesis, which was formed in the late 1970s (to the ignorance of the US government at the time) was based on years of data taken on Juneau Icefields.

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