Temps de lecture :5 minutes
In both polar regions, there is strong evidence of the ongoing impacts of climate change on terrestrial and freshwater species, communities and ecosystems (very high confidence).
Recent studies project that such changes will continue (high confidence), with implications for biological resources and globally important feedbacks to climate (mediumconfidence). […]
The polar regions are increasingly recognised as being:
• geopolitically and economically important,
• extremely vulnerable to current and projected climate change,
• the regions with the greatest potential to affect global climate and thus human populations and biodiversity.
Key regional projections highlighted in the TAR (Third Assessment Report, Anisimov et al., 2001)
• Increased melting of Arctic glaciers and the Greenland ice sheet, but thickening of the Antarctic ice sheet due to increased precipitation, were projected.
• Substantial loss of sea ice at both poles was projected.
• Reduction of permafrost area and extensive thickening of the active layer in the Arctic was expected to lead to altered landscapes and damage to infrastructure.
• Climate change combined with other stresses was projected to affect human Arctic communities, with particularly disruptive impacts on indigenous peoples following traditional and subsistence lifestyles.
• Economic costs and benefits were expected to vary among regions and communities.
• Changes in albedo due to reduced sea-ice and snow extent were expected to cause additional heating of the surface and further reductions in ice/snow cover.
For several decades, surface air temperatures in the Arctic have warmed at approximately twice the global rate (McBean et al., 2005). The areally averaged warming north of 60°N has been 1-2°C since a temperature minimum in the 1960s and 1970s. In the marineArctic, the 20th-century temperature record is marked by strong low-frequency (multi-decadal) variations
(Polyakov et al., 2002). […]
The most recent (1980 to present) warming of much of the Arctic is strongest (about 1°C/decade) in winter and spring, and smallest in autumn; it is strongest over the interior portions of northern Asia and north-western NorthAmerica (McBean et al., 2005). The latter regions, together with the Antarctic Peninsula, have been the most rapidly warming areas of the globe over the past several decades (Turner et al., 2007). The North Atlantic sub-polar seas show little warming during the same time period, probably because of their intimate connection with the cold, deep waters. Temperatures in the upper troposphere and stratosphere of the Arctic have cooled in recent decades, consistent with increases in greenhouse gases and with decreases in stratospheric ozone since 1979 (Weatherhead et al., 2005).
Precipitation in theArctic shows signs of an increase over the past century, although the trends are small (about 1% per decade), highly variable in space, and highly uncertain because of deficiencies in the precipitation measurement network (McBean et al., 2005) and the difficulty in obtaining accurate measurements of rain and snow in windy polar regions. There is no evidence of systematic increases in intense storms in the Arctic (Atkinson, 2005) although coastal vulnerability to storms is increasing with the retreat of sea ice.
[…] Changes in vegetation, particularly a transition from grasses to shrubs, have been reported in the NorthAmericanArctic (Sturmet al., 2001) and elsewhere (Tape et al., 2006), and satellite imagery has indicated an increase in the Normalised Difference Vegetation Index (NDVI, a measure of photosynthetically active biomass) over much of the Arctic (Slayback et al., 2003). This is consistent with a longer growing season and with documented changes in the seasonal variation in atmospheric CO2 concentrations as reported in the TAR. […]
The Arctic is now home to approximately 4 million residents (Bogoyavlenskiy and Siggner, 2004). Migration into the Arctic during the 20th century has resulted in a change of demographics such that indigenous peoples now represent 10% of the entire population. This influx has brought various forms of social, cultural and economic change (Huntington, 1992; Nuttall, 2000b). For most Arctic countries, only a small proportion of their total population lives in the Arctic, and settlement remains generally sparse (Bogoyavlenskiy and Siggner, 2004) and nomadic peoples are still significant in some countries. On average, however, two thirds of the Arctic population live in settlements with more than 5,000 inhabitants. Indigenous residents have, in most regions, been encouraged to become permanent residents in fixed locations, which has had a predominantly negative effect on subsistence activities and some aspects of community health. At the same time, Arctic residents have experienced an increase in access to treated water supplies, sewage disposal, health care facilities and services, and improved transportation infrastructure which has increased access to such things as outside market food items (Hild and Stordhal, 2004). In general, the Arctic has a young, rapidly growing population with higher birth rates than their national averages, and rising but lower than national average lifeexpectancy. This is particularly true for indigenous populations, although some exceptions exist, such as in the Russian north, where population and life-expectancy has decreased since 1990 (Einarsson et al., 2004).
Political and administrative regimes in Arctic regions vary between countries. In particular, indigenous groups have different levels of self-determination and autonomy. Some regions (e.g., northern Canada and Greenland) now have formalised land-claim settlements, while in Eurasia indigenous claims have only recently begun to be addressed (Freeman, 2000). Wildlife management regimes and indigenous/non-indigenous roles in resource management also vary between regions. Nowadays, large-scale resource extraction initiatives and/or forms of social support play significant roles in the economies of many communities. Despite these changes, aspects of subsistence and pastoral livelihoods remain important.
Regardless of its small and dispersed population, the Arctic has become increasingly important in global politics and economies. For example, the deleterious effect on the health of Arctic residents of contaminants produced in other parts of the world has led to international agreements such as the Stockholm Convention on Persistent Organic Pollutants (Downey and Fenge, 2003). Furthermore, significant oil, gas and mineral resources (e.g., diamonds) are still to be developed in circum-Arctic regions that will further increase the importance of this region in the world (e.g., U.S. Geological SurveyWorld Energy Assessment Team, 2000; Laherre, 2001).
In Arctic ecosystems, adaptive capacity varies across species groups from plants that reproduce by cloning, which have relatively low adaptive potential, through some insects (e.g., Strathdee et al., 1993) that can adapt their life cycles, to micro-organisms that have great adaptive potential because of rapid turnover and universal dispersal. The adaptive capacity of current Arctic ecosystems is small because their extent is likely to be reduced substantially by compression between the general northwards expansion of forest, the current coastline and longerterm flooding of northern coastal wetlands as the sea level rises, and also as habitat is lost to land use. General vulnerability to warming and lack of adaptive capacity ofArctic species and ecosystems are likely, as in the past, to lead to relocation rather than rapid adaptation to new climates.
[…] A change from Arctic to sub-Arctic conditions is happening with a northward movement of the pelagic-dominated marine ecosystem that was previously confined to the south-eastern Bering Sea. Thus communities that consist of organisms such as bottom-feeding birds and marine mammals are being replaced by communities dominated by pelagic fish. Changes in sea ice conditions have also affected subsistence and commercial harvests (Grebmeier et al., 2006).
Many Arctic and sub-Arctic seas (e.g., parts of the Bering and Barents Seas) are among the most productive in the world (Sakshaug, 2003), and yield about 7Mt of fish per year, provide about US$15 billion in earnings (Vilhjálmsson et al., 2005), and employ 0.6 to 1 million people (Agnarsson and Arnason, 2003).
In addition, Arctic marine ecosystems are important to indigenous peoples and rural communities following traditional and subsistence lifestyles (Vilhjálmsson et al., 2005).
Recent studies reveal that sea surface warming in the northeast Atlantic is accompanied by increasing abundance of the largest phytoplankton in cooler regions and their decreasing abundance in warmer regions (Richardson and Schoeman, 2004). In addition, the seasonal cycles of activities of marine micro-organisms and invertebrates and differences in the way components of pelagic communities respond to change, are leading to the activities of prey species and their predators becoming out of step. Continued warming is therefore likely to impact on the community composition and the numbers of primary and secondary producers, with consequential stresses on higher trophic levels. This will impact economically important species, primarily fish, and dependent predators such as marine mammals and sea birds (Edwards and Richardson, 2004).