Research
Climate
The
climate of Northern Alaska can be divided onto three different zones: Arctic
Coastal, Arctic Inland and Arctic Foothills. Extending 20 km from the ocean,
the 1002 area falls under the category of Arctic Coastal, which is
characterized by cool summers and relatively warm winters, due to the impact of
the ocean. Partially due to the rain shadow created by the Brooks Range just
south of the coastal plain, the region has the lowest precipitation, 50 percent
of which falls as snow. The air temperatures remain below freezing through most
of the year and snow covers the ground surface for more than 8 months from
October through April (Zhang, Osterkamp 1996).
Temperatures
The mean annual air temperature at Barrow for the period from 1987 through
1992 was -12.3 degrees Centigrade. The winter season prevails from September
through May. Temperatures increase dramatically as we move inland from the
coast towards the Brooks Range. (Zhang, Osterkamp 1996). Temperatures
reach a high of about 86 degrees F in the summer (averaging about 41 degrees)
yet drops to well below zero (averaging -4 degrees) in the winter. The global
warming trend has already increased temperatures in the Arctic by 5 degrees F
and 8 degrees in the winter since the 1960s, leading to shorter ice seasons,
glacier melting, permafrost thaw, and increased precipitation. The inevitable
change in climate may lengthen the growing season, but it will also alter the
delicate ecological balance in ANWR (anwr.org).
Precipitation
Measuring
precipitation in a wind-swept region, especially where the total quantity is
small and more than 50 percent comes as snow, is a complicated problem. ANWR
has an average rainfall of about 25cm, and solid winter precipitation for
coastal areas averaged 15.3cm for the three years of study 1994-97. Out of this
34 percent of the precipitation sublimed (Sturm 2002).
During
the winter months, virtually all precipitation falls in solid form. The
low-growing vegetation and high wind speeds that characterize the domain allow
significant wind redistribution of snow throughout the winter. This means that
snow depths can be quite variable and, under appropriate conditions, some of
the snow cover is returned to the atmosphere by blowing snow sublimation.
Winter precipitation measurements do not exist in wind-blown arctic regions
(Sturm 2002).
Snow
cover
Snow
cover possesses certain thermal properties which compete with air temperature
on the ground thermal regime. It has high reflectivity and emissivity that cool
the snow’s surface; snow cover is a good insulator that insulates the ground;
and melting snow is a heat sink, owing to its latent heat of fusion (Zhang et
al., 1997). In spite of the high albedo from spring and early summer snow and
cloud cover, net radiation is positive throughout the year (Hare, F. K. 1972).
The
microclimate of an environment, or the climate near the ground, is largely a
function of energy exchange phenomena at the ground-air interface. The average
maximum thickness of the seasonal snow cover varied from about 30cm along the
Arctic coast to about 40cm inland for the period from 1977 through 1988 (Zhang
et al., 1996a). The thickness of seasonal snow cover, however, can vary
substantially on a micro scale due to the impact of wind, ground surface
morphology, and vegetation. Along the Arctic Coastal Plain, the ground surface
is relatively flat and mainly occupied by low-center polygons. Vegetation is
poorly developed, and the region experiences high wind speeds during the winter
months (Haugen 1982).
In this setting, the snow can be either blown away or well packed by strong wind,
reducing the insulating effect. Inland, the ground surface becomes rough and
vegetation changes significantly as a result of increased summer warmth. Wind
redistributes the snow which is better trapped in the troughs and depressions
created by rough micro relief and the taller vegetation. The trapped
snow increases the insulating effect of the seasonal snow cover, which, in
turn, influences the permafrost conditions that determine vegetation of the
area. On a monthly basis, seasonal snow cover warms the ground surface during
winter months but cools it during the period of snowmelt. On an annual basis
the seasonal snow cover definitely warms the ground surface. (Zhang et al.,
1997)
In contrast with the Arctic coast, the Arctic inland and Arctic foothills feature
lower wind speed, a very rough surface with tussocks, troughs and depressions,
and well-developed vegetation. Snow can be interrupted and trapped by
vegetation and rough surface, increasing the insulating effect and permafrost
temperatures.
Effects of Global Warming
Climatic
warming associated with elevated levels of greenhouse gases in the atmosphere
is predicted to be greater in the Arctic than elsewhere, almost two to three
times more than the global average (Osterkamp 1982). The impact of climatic
warming on the Arctic ecosystem is uncertain, as are the feedback processes to
potential changes in the exchange of greenhouse gases between the polar soil
and atmosphere. This will be discussed further with relation to soil and the
carbon cycle. One of the main reasons is that climatic conditions on the north
slope of Alaska are not well understood owing to the sparsity of meteorological
stations and discontinuity of observations.
Analyses
of data collected by a number of studies done from the late 1940s onwards at
and around Barrow and Prudhoe Bay showed that the permafrost surface has warmed
2º to 4º C in the Alaskan Arctic over the last century (Lachenbruch and
Marshall 1986; Lachenbruch et al., 1988). Since then, the rate of increase in
temperature has accelerated greatly, to about 1º C per decade. Snow and shrubs
form a positive feedback loop that could change land surface processes in the
Arctic. The increased subnivian soil temperatues that are observed would
produce conditions favorable to shrub growth (i.e. more decomposition and
nutrient mineralization) (Strum et al., 2001). Aerial photographs taken of
Alaska's North Slope during the 1940s offer some of the best evidence of such
change: a dramatic increase in the growth of trees and shrubs in the Arctic.
Sources:
Effects of Climate on the Active Layer and Permafrost on the
North Slope of Alaska, U.S.A. T. Zhang, T. E. Osterkamp and K. Stamnes
1997 (Geophysical Institute, University of Alaska, Fairbanks)
Climate
of Remote Areas in North Central. Alaska 1975-1979, Summary
Haugen, R. K.
(1982)
Permafrost Temperatures and the Changing Climate.
Lachenbruch,
A. H., Cladouhos, T. T. and Saltus, R. W. (1988)
Changing Climate:
geothermal evidence from permafrost in the Alaskan
Arctic. Science, 234,
689-696
Lachenbruch, A. H. and Marshell, B. V. (1986)
Some
Characteristics of the Climate in Northern Alaska
Zhang, T., Osterkamp, T. E.
and Stamnes, K. (1996a)
Potential Impact of a warmer climate on
permafrost in Alaska
Osterkamp, T. E. (1982)
Snow-shrub
interactions in the Arctic tundra: A hypothesis with
climatic