Environmental Engineering Reference
In-Depth Information
compared to winter. Figure O.4 illustrates that the retreat of Arctic sea ice
is more compact when plotted versus global mean temperature rather than
time, and this aids the understanding of the effect of stabilization at various
target levels. Published studies of the range of the date when late summer
Arctic sea ice is expected to disappear range from 2037 to beyond 2100.
Models suggest that late summer Arctic sea ice decreases rapidly if warming
exceeds about 2°C. By the end of the 21st century (global warming of about
3-5°C relative to pre-industrial conditions) an ice-free Arctic ocean in late
summer is predicted by most models. In the decades after 2100, two models
suggest that ice-free conditions may occur in winter if polar temperatures
reach 13°C above present-day values. In the Antarctic, models predict a loss
in ice cover ranging from 10-50% in winter and 33-100% in summer for a
warming of about 1.7-4.4°C. The relationship between annual average sea
ice area and the global average temperature suggests that ice recovery may
occur if temperatures decrease. {4.7}
Snow Cover and Snowpack
Current trends in snow cover over the Northern Hemisphere suggest
that the snow cover season has shortened and spring melt is occurring
earlier compared to the past 50-100 years. Modelled changes in Northern
Hemisphere snow cover are similar to the observations. Future decreases
are consistent across the models and may reach -18% by 2090 (or a global
warming of about 2-3°C). Snowpack has decreased over much of western
North America since
1925, and this decrease has been linked to increas-
ing temperatures over the West.
While regional responses to the warmer
surface temperatures may vary, the overall response suggests a significantly
shorter snow season, smaller areal coverage, an earlier start to the melt
season, a later start to the accumulation season, and decreased snowpack
as the climate warms. The regions that show the most sensitivity to warm-
ing conditions are in maritime areas (both at low elevation and mountain-
ous) while the continental interiors respond more slowly. The percentage
change is largest in summer, but the greatest areal reductions are expected
in spring. {4.7}
Permafrost
Northern Hemisphere permafrost is expected to degrade under global
warming.
Permafrost extent is expected to shrink, the region to retreat pole-
ward, and the active layer to deepen as its temperature increases. These
