16 Polar Regions (Arctic and Antarctic) OLEG ANISIMOV (RUSSIA) AND BLAIR FITZHARRIS (NEW ZEALAND) Lead Authors: J.O. Hagen (Norway), R. Jefferies (Canada), H. Marchant (Australia), F. Nelson (USA), T. Prowse (Canada), D.G. Vaughan (UK) Contributing Authors: I. Borzenkova (Russia), D. Forbes (Canada), K.M. Hinkel (USA), K. Kobak (Russia), H. Loeng (Norway), T. Root (USA), N. Shiklomanov (Russia), B. Sinclair (New Zealand), P. Skvarca (Argentina) Review Editors: Qin Dahe (China) and B. Maxwell (Canada) CONTENTS Executive Summary 80 3 16 . 2 . 6 . Arctic Hydrology 82 1 16 . 2 . 6 . 1 . Changes in Precipitation, Snow 16 . 1 . Po l a r Re g i o n s 80 7 Accumulation, and Spring Melt 82 3 16 . 1 . 1 . Previous Work—Summary of Special Report 16 . 2 . 6 . 2 . Surface Water Budgets on Regional Impacts of Climate Change 80 7 and Wet l a n d s 82 3 16 . 1 . 2 . Distinctive Characteristics of Polar Regions 80 9 16 . 2 . 6 . 3 . Ecological Impact of 16 . 1 . 3 . Climate Change in the 20th Century 81 0 Changing Runoff Regimes 82 3 16 . 1 . 3 . 1 . The Arctic 81 0 16 . 2 . 6 . 4 . Sensitivity of Arctic Ocean 16 . 1 . 3 . 2 . The An t a r c t i c 81 2 to River Flow 82 4 16 . 1 . 4 . Scenarios of Future Change 81 3 16 . 2 . 7 . Changes in Arctic Biota 82 4 16 . 2 . 7 . 1 . Impacts of Climate Change on 16 . 2 . Key Regional Concerns 81 4 Arctic Terrestrial Environments 82 4 16 . 2 . 1 . Changes in Ice Sheets and Glaciers 81 4 16 . 2 . 7 . 2 . Response of Ar c t i c 16 . 2 . 2 . Changes around the Antarctic Peninsula 81 5 Plant Communities 82 5 16 . 2 . 3 . Changes in the Southern Ocean 16 . 2 . 7 . 3 . Changes in Arctic An i m a l s 82 6 and Impacts on its Life 81 5 16 . 2 . 8 . Impact on Human Communities in the Ar c t i c 82 6 1 6 . 2 . 3 . 1 .O v e r v i e w 81 5 16 . 2 . 8 . 1 . Impacts on Indigenous Peoples 82 6 16 . 2 . 3 . 2 . Role of Ocean Changes 81 5 16 . 2 . 8 . 2 . Impacts on Economic Ac t i v i t y 82 7 16 . 2 . 3 . 3 . Role of Ice Shelves 81 6 16 . 2 . 3 . 4 . Impacts on Biology 16 . 3 . Sy n t h e s i s 82 9 of the Southern Ocean 81 7 16 . 3 . 1 . Feedbacks and Interactions—Polar Drivers 82 9 16 . 2 . 4 . Changes in Sea Ice 81 9 16 . 3 . 2 . Adaptation Potential and Vul n e r a b i l i t y 83 1 16 . 2 . 4 . 1 . Sea Ice in the Arctic Ocean 81 9 16 . 3 . 3 . Development, Sustainability, and Equity 83 1 16 . 2 . 4 . 2 . Sea Ice in the Southern Ocean 82 0 16 . 3 . 4 . Uncertainties and Risks 83 1 16 . 2 . 5 . Pe r m a f r o s t 82 0 16 . 2 . 5 . 1 . Temperature Ar c h i v e 82 0 Re f e re n c e s 83 2 16 . 2 . 5 . 2 . Predicted Changes in Permafrost 82 1 16 . 2 . 5 . 3 . Environmental Impacts 82 1 EXECUTIVE SUMMARY In this summary we indicate our uncertainty in observations, Impacts mechanisms, and scenarios by using a five-point scale, from “very high confidence” (*****) to “very low confidence” (*). Substantial warming and increases in precipitation are projected for polar regions over the 21st century by almost all climate models. There are eight key concerns related to the impact of Climate Changes in the 20th Century this climate change in the Arctic and Antarctic. Associated with these concerns will be changes to the atmosphere and the Although there are some regional anomalies, there is strong oceans that will propagate to other regions of the world: evidence that climate change has had an impact in the Arctic and the Antarctic. Many documented changes already parallel 1) Changes in ice sheets and polar glaciers: Increased those forecast to result from climate change: melting is expected on Arctic glaciers and the Greenland ice sheet, and they will retreat and thin close • In the Arctic, extensive land areas show a 20th-century to their margins. Most of the Antarctic ice sheet is likely warming trend in air temperature of as much as 5°C. to thicken as a result of increased precipitation. There is Over sea ice, there has been slight warming in the a small risk, however, that the West Antarctic and 1961–1990 period.***** Precipitation has increased.** Greenland ice sheets will retreat in coming centuries. • Arctic sea-ice extent has decreased by 2.9% per decade To g e t h e r, these cryospheric changes may make a over the 1978–1996 period; sea ice has thinned, and s i gnificant contribution to sea-level rise.**** there are now more melt days per summer. Sea-ice 2) Changes around the Antarctic Peninsula: This region extent in the Nordic seas has decreased by 30% over has experienced spectacular retreat and collapse of ice the past 130 years.***** It is not yet clear whether shelves, which has been related to a southerly migration changes in sea ice of the past few decades are linked to of the January 0°C isotherm resulting from regional a natural cycle in climate variability or have resulted warming. The loss of these ice shelves has few direct explicitly from global warming. impacts. Projected warming is likely, however, to break • Atlantic water flowing into the Arctic Ocean has warmed, up ice shelves further south on the Antarctic Peninsula, and the surface layer has become thinner. The mixed expose more bare ground, and cause changes in layer in the Beaufort Sea has become less saline.**** t e r r e strial biology, such as introduction of exotic • Regions underlain by permafrost have been reduced in plants and animals.**** extent, and a general warming of ground temperatures 3) Changes in the Southern Ocean and impacts on its life: has been observed in many areas.***** Climate change is likely to produce long-term—perhaps • There has been a statistically significant decrease in irreversible—changes in the physical oceanography and spring snow extent over Eurasia since 1915.**** ecology of the Southern Ocean. Projected reductions in • In summary, many observations of environmental sea-ice extent will alter under-ice biota and spring bloom change in the Arctic show a trend that is consistent in the sea-ice marginal zone and will cause profound with warming and similar to that predicted by general impacts at all levels in the food chain, from algae to circulation models (GCMs). krill to the great whales. Marine mammals and birds, • In the Antarctic, over the past half-century there has which have life histories that tie them to specific breeding been a marked warming trend in the A n t a r c t i c sites, will be severely affected by shifts in their foraging Peninsula.**** Elsewhere there is a general but not habitats and migration of prey species. Warmer water unambiguous warming trend.** will potentially intensify biological activity and growth • Precipitation in the Antarctic has increased.* rates of fish. Ultimately, this should lead to an increase • Satellite observations show no significant change in in the catch of marketable fish, and retreat of sea ice Antarctic sea-ice extent over the 1973–1996 period.***** will provide easier access to southern fisheries.*** Analysis of whaling records and modeling studies 4) Changes in sea ice:There will be substantial loss of sea i n d icate that Antarctic sea ice retreated south by 2.8 ice in the Arctic Ocean. Predictions for summer ice degrees of latitude between the mid-1950s and the early indicate that its extent could shrink by 60% for a doubling 1970s.*** of carbon dioxide (CO2), opening new sea routes. This will • Surface waters of the Southern Ocean have warmed have major trading and strategic implications. With more and become less saline.*** open water, there will be a moderation of temperatures 804 Polar Regions (Arctic and Antarctic) and an increase in precipitation in Arctic lands. food species will affect hunting and gathering practices Antarctic sea-ice volume is predicted to decrease by and could threaten longstanding traditions and ways of 25% or more for a doubling of CO2, with sea ice life. On the other hand, communities that practice these retreating about 2 degrees of latitude.**** lifestyles may be sufficiently resilient to cope with 5) Changes in permafros t : Thickening of the seasonally these changes. Increased economic costs are expected thawed layer above permafrost (active layer) is expected. to affect infrastructure, in response to thawing of Modeling studies indicate that large areas of permafrost p e rmafrost and reduced transportation capabilities terrain will begin to thaw, leading to changes in across frozen ground and water. However, there will be drainage, increased mass movements, thermal erosion, and economic benefits—including new opportunities for altered landscapes in much of the Arctic and subarctic. trade and shipping across the Arctic Ocean, lower Warming of permafrost, thawing of ground ice, and o p e rational costs for the oil and gas industry, lower development of thermokarst terrain have been documented heating costs, and easier access for ship-based over the past several decades. In developed areas of the tourism.***** Arctic, continuation of such changes may lead to costly damage to human infrastructure.**** 6) Changes in Ar ctic hydrol o g y : The hydrology of the Feedbacks and Interactions Arctic is particularly susceptible to warming because small rises in temperature will result in increased melting Climate change and global warming will affect key polar drivers of snow and ice, with consequent impacts on the water of further climate change.