Permafrost

used for construction on permafrost in the regions with high salinity. It is important at
calculations and design decisions at the choice of places of drilling of oil and gas wells.
Key words: Frozen ground, cooled ground, salinity, physical state of permafrost
198
Questions Regarding the Recent Warming of Permafrost in Alaska
T. E. Osterkamp
(Geophysical Institute, University of Alaska, Fairbanks, AK 99775)
Abstract: Permafrost has warmed significantly throughout much of Alaska over the past
quarter century. There are a number of questions that arise for any systematic warming of
permafrost. These include questions regarding the timing, magnitude, spatial distribution,
seasonal distribution, effects on the active layer, thawing effects, thermokarst, and cause(s) of
the warming. This paper reviews permafrost research conducted over this time period and
attempts to provide at least partial answers to these questions.
Permafrost temperatures have warmed throughout much of the state coincident with a
statewide warming of air temperatures that began in 1977. The permafrost temperatures peaked
in the early 1980s and then decreased in response to slightly cooler air temperatures and thinner
snow covers. Arctic sites began warming again typically about 1986 and Interior Alaska sites
about 1988. Gulkana, the southernmost site, has been warming slowly since it was drilled in
1983. Air temperatures were relatively warm and snow covers were thicker-than-normal from
the late 1980s into the late 1990s allowing permafrost temperatures to continue to warm.
Temperatures at some sites leveled off or cooled slightly at the turn of the century. Two sites
(Yukon River Bridge and Livengood) cooled during the period of observations.
The magnitude of the total warming at the surface of the permafrost (through 2003) was 3
to 4 °C for the Arctic Coastal Plain, 1 to 2 °C for the Brooks Range including its northern and
southern foothills, and 0.3 to 1 °C south of the Yukon River.
Sparse data indicates that permafrost is warming throughout the region north of the Brooks
Range from the Chukchi Sea to the Canadian border, southward along a north-south transect
from the Brooks Range to the Chugach Mountains (except for Yukon River and Livengood), in
Interior Alaska throughout the Tanana River region, and southward through the Alaska Range in
a broad band to Anchorage in the west and Tok in the east including the Copper River Valley
and the Wrangell Mountains.
At two sites on the Arctic Coastal Plain, the warming was seasonal, greatest during
“winter” months (October through May) and least during “summer” months (June through
September).
Active layer thicknesses depend largely on the thermal history of the ground surface
during the summer thaw period. This explains why the observed winter warming of air, ground
and permafrost temperatures has produced little change in annual maximum active layer
thicknesses.
Near Healy, permafrost has been thawing at the top since the late 1980s at about 10
cm/year. Maximum settlement is about 1 ½ m. At Gulkana, permafrost was thawing from the