Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 281

taliks. They are unfrozen zones in permafrost below parts of the Arctic shoreline or below
some lakes or they exist as soil brine pockets.
Climate, especially air temperature, is one of the main factors controlling the spatial
extentanddepthofthepermafrostlayerandwehavealreadyseenthattheannualmeansur-
face air temperature over Arctic land areas has risen by about 2°C since the mid-1960s. It
is therefore not surprising to see that the 2011 SWIPA team found that permafrost temper-
atures since the late 1970s have increased at monitoring sites throughout the Arctic, includ-
ingNorthAmerica, RussiaandScandinavia, by0.5to2°C.Similarly,active layerthickness
over the last two decades has increased at sites in Scandinavia, Russia and (in the last few
years) in Alaska but not in Canada.
From the earlier paragraph, you will have noticed that not all permafrost is at the same
temperature. As would be expected, warmer permafrost with temperatures close to 0°C oc-
curs at southern permafrost margins and in the discontinuous zone. More northerly cold
permafrost can have temperatures as low as −12°C to −15°C. Interestingly, warm ice-rich
permafrost shows lower warming rates than areas with cold permafrost. This is because of
latent heat effects associated with the phase changes of thawing that dominate an ice-rich
soil environment. Nevertheless, because of the huge extent of deep, cold permafrost, it is
the warm permafrost regions that are more prone to loss under present conditions of Arctic
warming.
The vertical profile of a column of permafrost reflects its history. Therefore, the upper
and youngest part of the column dates from the Little Ice Age, below which we find ice
from the late to mid-Holocene, while at the bottom rests the oldest permafrost, dating from
the late Pleistocene.
What can we expect inthe future? Forward-looking projections ofgroundtemperature
in the circumpolar Arctic suggest that late Holocene age permafrost will be thawing at the
southern limit of the permafrost zone by the end of the twenty-first century. At that time,
even late Pleistocene permafrost could be thawing at some locations. Regional models add
a further perspective. In Russia, which is home to most of the Northern Hemisphere's per-
mafrost, increases in ground temperature of 0.6 to 1°C have been projected by 2020. In