Climate of the polar realms - The Global Climate System: Patterns, Processes, and Teleconnections - page 166

chlorine chemistry processes if the temperatures fall below 200 K. As a result,
''pockets'' of ozone depletion occur for relatively short periods of time, due to
chlorine chemistry. These are highly variable in location. Pockets can occur
outside the vortex on occasion (Bobylev et al. 2003 ), but these are created by a
decrease in single oxygen production, and not chlorine chemistry. Since people
live in the higher latitudes of the Northern Hemisphere, such pockets are of
concern to human health, due to risks from increased ultraviolet radiation.
5.13 Concerns about future warming
The Arctic atmosphere is far less isolated from the interactions with the rest of
the atmosphere than the Antarctic. While there is evidence of recent warming in
both locations, sometimes attributed to the greenhouse effect, the potential
impacts in the Arctic are currently of greater concern (Whitfield et al. 2004
and others). Bobylev et al.( 2003 ) review the summaries from IPCC ( 2001 )
regarding near-future climate change in the Arctic, associated with greenhouse
warming. Results from combined model scenarios indicate that, by the end of the
twenty-first century, warming in the Arctic will be 40% greater than the global
average. The Arctic Ocean is likely to become nearly ice-free, creating large
reductions in albedo and major changes in the structure of the energy budget.
Open water rather than ice will result in increased carbon dioxide absorption and
changes in the marine ecosystem. Further changes include ocean circulation,
meltwater pathways, reductions in deepwater formation and so forth. The inter-
action between the all-ocean surface and the atmosphere will create a different
feedback system than that occurring now with the ice pack, resulting in changes
in precipitation distribution, surface temperatures, and atmospheric circulation.
The complexities of what is likely to occur are not well understood.
5.14 Chapter summary
Table 5.4 summarizes the major geographical and climate characteristics of the
Arctic and Antarctic regions. Although the mid-troposphere and lower strato-
sphere circulation over both areas is broadly similar (meridional heat and
moisture transport toward the poles; subsidence of cold air from the stratosphere
especially in winter), the surface environments create major differences in wind
flows, cyclogenesis, distribution of extra-tropical lows, temperature, and pre-
cipitation. At both locations, the geographical distribution of land, water, and ice
has a critical role in the seasonal and spatial climate pattern. Models suggest that
both regions will warm in greenhouse scenarios. The main consequences for the
Antarctic may be more precipitation and thinning of the surrounding ice shelf.
For the Arctic, open water may replace the ice pack by the end of the twenty-first
century, creating major changes in radiation budgets, circulation, precipitation,
and temperature.