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GLOBAL ENVIRONMENTAL CHANGE: Research Pathways for the Next Decade
Several of the major climate patterns, for example, the PNA and NAO, extend well into the polar regions (focal points of the cryosphere). Variations in the indices describing these patterns seem to be dominated by changes in the low-pressure systems in the northern extremes of these patterns. That is, changes in the Aleutian Low influence the PNA index, and the Icelandic Low influences the NAO index. These influences reflect the fact that the subpolar low appears to be less stable than the rather statically positioned, midlatitude, high-pressure ridges that control the indices' other limits. These low-pressure cells show considerable migration and variability in strength. Since they extend well into the polar regions and show some dependence on the regional SST at their lower surfaces, we might expect that they will show some dependence on the ice and snow distributions as well. The overlap also allows the patterns to bridge the high-and midlatitude zones, representing an obvious avenue through which coherent climate variations and change may be propagated between these latitudes. Also, some preliminary model studies57 suggest that the modeled anthropogenic greenhouse distribution of surface warming differs from a natural pattern associated with the COWL distribution only with the former extending farther into the polar regions.
Previously, analyses of climate patterns neglected the polar regions, owing to the paucity of data on those locations. However, recently released historical Russian and U.S. data now allow inclusion of these regions into such analyses. It is thus now possible as well as important to identify the polar contribution and signature to these patterns. It is also essential to identify the sensitivity and dependencies of the patterns on crysophere characteristics, particularly the fairly mutable and mobile sea ice cover and snow fields. Finally, because the Antarctic Circumpolar Wave and its covariation with ENSO seem to suggest a hemispherewide teleconnection between the tropics and extratropics in the poorly examined southern hemisphere, we need to refine our understanding of the extent, nature, linkages, and controls of the Antarctic Circumpolar Wave with regard to extrapolar climate patterns (and climate in general).
In addition to issues related to climate patterns, a number of issues must be addressed to understand the nature and importance of cryosphere components in the global climate. Specifically, we need to determine parameterizations and sensitivities of the processes controlling several phenomena: (1) ice-albedo feedbacks, including spatial averaging of heterogeneous conditions; (2) snow-climate feedbacks, which are much like ice-albedo issues but for vast continental areas; (3) ice-cloud feedbacks; (4) ice-ocean feedbacks, including thermohaline circulation instabilities and interactions, surface stability influences, and ocean-ice interactions; and (5) ice sheet-ocean feedback and ice sheet instabilities.
One finding of tremendous interest in the past decade was the discovery that the ocean can generate an internal mode of variability over a variety of timescales. The nature, vigor, and characteristics of this variability are sensitive to the boundary conditions in thermohaline source regions, which are in the high latitudes and