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Figure 41.—A, Locations of University of Alaska borehole observatories (provided by
Vladimir Romanovsky, University of Alaska Fairbanks) and locations of the U.S.
Geological Survey (USGS) deep boreholes in northern Alaska (Lachenbruch and
Marshall, 1986); and B, Warming in degrees Celsius of permafrost at 20-m depth
between 1989 and 2007/2008 at USGS borehole sites within and admacent to National
Petroleum Reserve in Alaska (NPRA) (courtesy of Gary D. Clow, USGS). On A, NPRA is
the National Petroleum Reserve, Alaska; ANWR is Alaska National Wildlife Refuge.