Environmental Engineering Reference
In-Depth Information
changes in the permafrost are linked to increasing global temperatures,
and rates of degradation change with different emission scenarios such that
higher emissions promote faster degradation. Damage to infrastructure over
a region 1-4 million km
2
would be expected by the end of the 21st century
if average Arctic air temperature increased by 5.5°C above the year 2000
average. {4.7}
Ice Sheets and Glaciers
Ice mass loss is occurring in some parts of Greenland and Antarctica,
but contributions of the great ice sheets to sea level rise of coming decades
and the next century remain uncertain.
For 1993-2003, the estimated contri-
butions to sea level rise (SLR) integrated across the Greenland and Antarctic
ice sheets are 0.21±0.07 and 0.21±0.35 mm y
-1
, respectively (0.021±0.007
and 0.021±0.035 m if continued for a century). Greenland lost roughly
180±50 Gt y
-1
(0.5±0.14 mm y
-1
SLR) for the time period 2003-2007. Re-
cent observations have shown that changes in the rate of ice discharge into
the sea can occur far more rapidly than previously suspected. The pattern of
ice sheet change in Greenland is one of near-coastal thinning, primarily in
the south and west along fast-moving outlet glaciers, and increased ice melt
in the marginal region. However, the interior of the ice sheet is expected to
be less vulnerable to future changes than these edge regions. Furthermore,
current discharge rates may represent a transient instability, and whether
they will increase or decrease in the future is unknown. A doubling in ice
discharge along with a continued increase in surface melt using a “medium”
emission scenario (AR4 A1B) would increase the global sea level by about
0.16 m by 2100, with 0.09 m contribution from ice dynamics, and 0.07 m
from surface melt, respectively. The Antarctic ice sheet shows a pattern of
near balance for East Antarctica, and greater mass loss from West Antarctica
(including the Antarctic Peninsula) for the past few years; however, there is
no strong evidence for increasing Antarctic loss over the past two decades.
The Amundsen Coast basin (Pine Island ice and Thwaites Glacier) represents
a potential for up to 1.5 m of equivalent sea level if it were to be entirely
melted; doubling the current ice stream velocities in this region along with
accelerated ice loss for the Antarctic Peninsula could raise sea level globally
by 0.12 m in 2100. An increase in ice discharge has already been observed
in several regions in Greenland. Assuming a doubling in ice discharge for
outlet glaciers in Greenland and the Amundsen Coast basin in Antarctica,
both ice sheets together could contribute up to about 0.28 m sea level by
2100 under the AR4 A1B warming scenario. {4.8}
