Geoscience Reference
In-Depth Information
the year 2015, the Panama Canal is slated to have a new set of locks and other
improvements that will allow it to handle to more traffic and larger ships.
11.5
Concluding Remarks
The broad picture of Arctic change through the twenty-first century seems clear.
Building on the introduction to this chapter, the Arctic will become warmer than
today, and the rate of warming will be larger than that for the globe as a whole,
especially in autumn and early winter. Sea ice will continue to decline in extent and
thickness, helping, along with other processes, to fuel the outsized warming of the
Arctic. Like air temperature, the change will not be steady, but will instead appear
as an overall trend with strong imprints of natural variability. The Arctic Ocean is
likely to become essentially free of sea ice in late summer by sometime in the mid-
dle or later part of the century but perhaps earlier. Over land, there will be a gradual
replacement of tundra with shrub vegetation, and a shorter snow-covered season. It
appears that total precipitation will increase, which will likely be seen as increased
river discharge to the Arctic Ocean. The Greenland Ice Sheet will continue to lose
mass, likely at an accelerating rate.
However, as we have learned, not just in this chapter, but throughout this
topic, the future holds many uncertainties. Reducing these uncertainties repre-
sents a major challenge. Although coupled global climate models represent one
of our most important tools for understanding how the climate system will evolve
through the twenty-first century, they still have many shortcomings, particularly
with respect to projections on the regional scale. As just one example, although
many of the CMIP3 models produce patterns of atmospheric variability that
resemble the NAO, AO, PNA, PDO, and ENSO, there are significant biases in the
temporal and spatial characteristics of the patterns - many models either under
or over represent the strength of the patterns or incorrectly place the location of
the teleconnection “centers of action” (Stoner et al., 2009 ). This is a fundamental
problem in the Artic, where such modes of variability are known to have strong
imprints on climate and are likely to strongly shape the evolution of the system.
Also at issue are deficiencies in model representations of the surface energy bud-
get, ocean-sea ice-climate interactions, and associated feedbacks. The future of
the Greenland Ice Sheet and its contribution to sea level rise is especially difficult
to project because changes in climate and oceanic conditions may then lead to
changes in ice sheet dynamics involving backpressure effects, basal lubrication,
and other factors ( Chapter 8 ).
Better understanding the future course of the Arctic climate system certainly
requires improved models, but it is also increasingly necessary to break down tra-
ditional disciplinary barriers and develop a more system oriented approach. The
Arctic is the home of myriad climate interactions and feedbacks involving the atmo-
sphere, land, ocean, and cryosphere, which are in turn tightly coupled to the global
climate system. But it seems that the more we understand how the Arctic functions,
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