The polar regions will play a substantial role in driving global climate change through positive feedbacks to global warming. They also provide us with unparalleled records of that change. The most important uncertainties, risks, and thus targets for research are as follows:

• Ocean thermohaline circulation: Will downwelling in the North Atlantic and the Southern Ocean cease, causing a shutdown of the circulation of the global ocean? Or will this downwelling simply reduce and eventually recover with stabilization of GHGs? What is the role of changing input of freshwater from Arctic rivers?
• Antarctic ice sheet: What will be the contribution of the Antarctic ice sheets to global sea-level rise over the coming centuries? Although it is likely that the Antarctic ice sheet will provide some degree of mitigation of predicted sea-level rise, there is a small risk that the West Antarctic ice sheet (or portions of it) may retreat rapidly, causing a greater than predicted rise.
• Marine biology: What will be the response to predicted climate change of the structure of marine communities and the overall productivity of polar oceans? Uncertainty arises because existing biological models are not yet sufficiently developed to provide authoritative and quantitative estimates. There is some risk of unforeseen collapse of parts of the marine biological system, with consequent global effects—particularly on fisheries.
• Arctic ice sheets, glaciers, and ice caps: What is the current and future magnitude of freshwater input to the oceans from ice masses? What is the impact on global sea level and the thermohaline circulation on decadal to century time scales, and how can uncertainties in estimates be reduced?
• Permafrost: As ice-rich permafrost degrades, what will be the magnitude, spatial extent, and variability of its impacts? Will increases in the thickness of the active layer in currently cold, continuous permafrost be sufficient to cause widespread damage to human infrastructure? How important is soil organic carbon sequestered in the upper layer of permafrost in the context of the world carbon balance?
• Arctic hydrology: Will the balance between increased precipitation and evapotranspiration lead to a drier or wetter Arctic landscape? What will be the water balances of the large river basins that generate freshwater inflow to the Arctic Ocean?
• Arctic sea ice: Is it possible that with increased open water in the Arctic Ocean, summer sea ice in the Arctic eventually could disappear completely? The risk is that substantially more open water could generate large changes in regional climate for countries on the Arctic rim.
• Fluxes of greenhouse gases: What are the current and future fluxes of GHGs from polar oceans and landscapes? In particular, what is the likely future role of gas hydrates?
• Stresses on human communities in the Arctic: Can Arctic communities survive the combined stresses of globalization and marked changes in their local environments that may result from climate change? Traditional lifestyles will be threatened, but the communities that practice these lifestyles may be sufficiently resilient to cope with these changes, as they have in the recent and distant past.
  

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