Summary of Arctic Climate Impact Assessment conclusions
This article has been reviewed by the following Topic Editor: Sidney Draggan Ph.D.
This is Section 18.2 of the Arctic Climate Impact Assessment. Lead Author: Gunter Weller; Contributing Authors: Elizabeth Bush,Terry V. Callaghan, Robert Corell, Shari Fox, Christopher Furgal, Alf Håkon Hoel, Henry Huntington, Erland Källén, Vladimir M. Kattsov, David R. Klein, Harald Loeng, Marybeth Long Martello, Michael MacCracken, Mark Nuttall,Terry D. Prowse, Lars-Otto Reiersen, James D. Reist, Aapo Tanskanen, John E.Walsh, Betsy Weatherhead, Frederick J.Wrona
The climate of the Arctic has undergone rapid and dramatic shifts in the past and there is no reason that it could not experience similar changes in the future. Past changes show climatic cycles that have occurred regularly on time scales from decades to centuries and longer and are most likely to have been caused by oceanic and atmospheric variability and variations in solar intensity. Examples of long-term cooler and warmer climates were the Little Ice Age and the Medieval Warm Period, respectively, while short-term decadal cycles like the North Atlantic Oscillation and Pacific Decadal Oscillation, among others, have also been found to affect the arctic climate. Since the industrial revolution in the 19th century, anthropogenic greenhouse gas (GHG) emissions have added another major climate driver. In the 1940s, the Arctic experienced a warm period, like the rest of the planet, although it did not reach the level of the warming experienced in the 1990s. The IPCC stated that most of the global warming observed over the last 50 years is attributable to human activities[1], and there is new and strong evidence that in the Arctic much of the observed warming over this period is also due to human activities.
Chapter 2 discusses the arctic climate system and observed changes in arctic climate over recent decades. Many types of observations indicate that the climate of the Arctic is changing. For example, air temperatures are generally warmer, the extent and duration of snow and sea ice are diminishing, and permafrost is thawing. However, there are also some regions where cooling has occurred, and some areas where precipitation has increased. Reconstruction of the history of arctic climate over thousands to millions of years indicates that there have been very large changes in the past. Based on these indications that the arctic climate is sensitive to changes in natural forcing factors, it is very likely that human-induced factors, for example the rise in GHG concentrations and consequent enhancement of the global greenhouse effect, will lead to very large changes in climate, indeed, changes that will be much greater in the Arctic than at middle and lower latitudes.
Fig.
18.1. Present and projected boundaries of summer sea-ice extent,
permafrost, and the treeline. The changes are projected to occur over
different time periods. Changes in summer sea-ice extent will occur by
the end of the century, as projected by the five model composite used by
the ACIA (section 6.3, Figs. 6.3b and 6.9c). The projected changes in
the treeline by the end of the century are from a vegetation model
driven by output from the Hadley Centre model (section 7.1.1, Fig. 7.2
and section 7.5.3.2, Fig. 7.32). The change in the permafrost boundary
assumes that the present areas of discontinuous permafrost (section
6.6.1, Fig. 6.21, although published sources differ) will be free of any
permafrost in the future; this is likely to occur beyond the 21st
century but it is not certain how long it will take.
The observed temperature changes in the Arctic over the five-decade period from 1954 to 2003 are shown in Fig. 18.2. Owing to natural variations and the complex interactions of the climate system, the observed trends show variations within each region. Mean annual atmospheric surface temperature changes range from a 2 to 3 ºC warming in Alaska and Siberia to a cooling of up to 1 ºC in southern Greenland.Winter temperatures are up to 4 ºC warmer in Siberia and in the western Canadian Arctic.
Although some regions have cooled slightly the overall trend for the Arctic is a substantial warming over the last few decades. For the Arctic as a whole, the 20th century can be divided into two warming periods, bracketing a 20-year cooling period (approximately 1945 to 1966) in the middle of the century. This pattern is less evident in northern Canada than in some other areas of the Arctic.
Fig.
18.2. Change in observed surface air temperature between 1954 and 2003:
(a) annual mean; (b) winter (Chapman and Walsh, 2003, using data from
the Climatic Research Unit, University of East Anglia,
www.cru.uea.ac.uk/temperature).
The Canadian Archipelago and West Greenland did experience some cooling mid-century, although even then, there was substantial winter warming. The warming has been significant over the past few decades (1966 to 2003), particularly in the Northwest Territories – continuing the band of substantial warming across northwest North America that also covers Alaska and the Yukon – reaching an increase of 2 ºC per decade. This warming is most evident in winter and spring.A more detailed description of observed climate change is given in Chapter 2. The climate change for each of the four ACIA regions is summarized in section 18.3.
Observations of arctic precipitation are restricted to a limited network of stations and are often unreliable since winter snowfall is not accurately measured by existing gauges, due to drifting snow.Available records indicate 20thcentury increases in precipitation at high latitudes on the North American continent but little if any change in precipitation in the watersheds of the large Siberian rivers.
Rapid changes in regional climates (so-called regime shifts) are also evident in the climatic record. For example, in 1976 in the Bering Sea region there was a relatively sudden shift in prevailing climatic patterns, which included rapid warming and reduction in sea-ice extent. Such shifts have led to numerous, nearly instantaneous impacts on biota and ecosystems, as well as impacts on human communities and their interactions with the environment. Although such fluctuations are not fully understood and are therefore difficult to predict, regime shifts can be expected to continue to occur in the future, even as the baseline climate is also changing as a result of global warming (see section 18.4.3).
Indigenous observations of climate change, as discussed in Chapters 3 and 12, contribute to understanding of climate change and associated changes in the behavior and movement of animals. Through their various activities, which are closely linked to their surroundings, the indigenous peoples of the Arctic experience the climate in a very personal way. Over many generations and based on direct, everyday experience of living in the Arctic, they have developed specific ways of observing, interpreting, and adjusting to weather and climate changes. Based on careful observations, on which they often base life and death decisions and set priorities, indigenous peoples have come to possess a rich body of knowledge about their surroundings. Researchers are now working with indigenous peoples to learn from their observations and perspectives about the influences of climate change and weather events on the arctic environment and on their own lives and cultures. These studies are finding that the climate variations observed by indigenous people and by scientific observation are, for the most part, in good accord and often provide mutually reinforcing information.
The presently observed climate change is increasingly beyond the range experienced by the indigenous peoples in the past. These new conditions pose new risks to the lifestyles of the indigenous populations, as described in section 18.2.2. The magnitude of these threats is critically dependent on the rate at which change occurs. If change is slow, adaptation may be possible; if however, change is rapid, adaptation is very likely to be considerably more difficult, if possible at all in response to some types of impacts.
Recent observations by the indigenous peoples of the Arctic of major changes in the climate and associated impacts are summarized in Table 18.1. Taken together, the body of observations from people residing across the Arctic presents a compelling account of changes that are increasingly beyond what their experience tells them about the past.
Indigenous observations of climate and related environmental changes include many other effects on plants and animals that are important to them (Chapter 7). These observations provide evidence of nutritional stresses on many animals that are indicative of a changing environment and changes in food availability. New species, never before recorded in the Arctic, have also been observed. The distribution ranges of some species of birds, fish, and mammals now extend further to the north than in the past. These observations are significant for indigenous communities since changes likely to occur in traditional food resources will have both negative and positive impacts on the culture and economy of arctic peoples.
Table 18.1. Examples of indigenous observations of environmental change in the Arctic.This table is mainly based on Chapters 3 and 12.
| European Arctic | Canada and Greenland | Alaska | |
| Atmosphere/ weather/winds | Weather patterns are changing so fast that traditional methods of prediction are no longer applicable.Winters are warmer. Seasonal patterns have changed. | Weather patterns are changing so fast that traditional methods of prediction are no longer applicable.Winters are warmer.There has been cooling in Hudson Strait/Baffin Island area, but greater variability. | Weather patterns are changing so fast that traditional methods of prediction are no longer applicable.There are more storms and fewer calm days.Winters are shorter and warmer, summers longer and hotter. |
| Rain/snow | Rain is more frequent in winter than before.There are more freeze–thaw cycles, thus more trouble for reindeer grazing in winter. | Snow is melting earlier and some permanent snow patches disappear. There is less snow and more wind, producing snow conditions that do not allow igloo building. | There is less snow. |
| Ocean/sea ice | Later freeze-up and earlier breakup of sea ice. Shore-fast ice is melting faster, creating large areas of open water earlier in summer. | Sea ice is thinner and is forming later. | There is increased coastal erosion due to storms and lack of ice to protect the shoreline from waves. |
| Lakes/rivers/ permafrost | Ice on lakes and rivers is thinner. | Water levels in lakes and rivers are falling on the Canadian mainland.Thinner river ice affects caribou on migration (they fall through). Permafrost is thawing, slumping soil into rivers and draining lakes. | Lakes and wetlands are drying out. Permafrost thawing is affecting village water supply, sewage systems, and infrastructure. |
| Plants and animals | New species are moving into the region. | Caribou suffer from more insects; body condition has declined. Caribou migration routes have changed. | Trees and shrubs are advancing into tundra.There are die-offs of seabirds and marine mammals due to poor body condition. New species of insects are observed. |
In projections of future climate, uncertainties of many types can arise, especially for as complex a challenge as projecting ahead 100 years. The ACIA adopted a lexicon of terms (section 1.3.3) describing the likelihood of expected change (Fig. 18.3). These terms are used throughout this chapter, and in all ACIA documents.
Fig. 18.3. Five-tier lexicon describing the likelihood of expected change.
Chapter 4 presents the ACIA projections of future changes in arctic climate. These projections extend the IPCC assessment[2] by presenting regional (north of 60º N) climate parameters, derived from global model outputs. The ACIA used five different global climate models (CGCM2, Canadian Centre for Climate Modelling and Analysis; CSM_1.4, National Center for Atmospheric Research, United States; ECHAM4/ OPYC3, Max Planck Institute for Meteorology, Germany; GFDL-R30_c, Geophysical Fluid Dynamics Laboratory, United States; and HadCM3, Hadley Centre for Climate Prediction and Research, United Kingdom) forced with two different emissions (GHG and aerosol) scenarios. The emissions scenarios are the B2 and A2 scenarios drawn from the IPCC Special Report on Emissions Scenarios[3]. The A2 emissions scenario assumes global emphasis on sustained economic development while the B2 emissions scenario reflects a world that promotes environmental sustainability. Neither scenario is considered an upper or lower bound on possible levels of future emissions. The climatic and environmental changes in the Arctic projected using the two scenarios are similar through about 2040, but diverge thereafter, with projections forced with the A2 emissions scenario showing greater warming.
These projections are not intended to capture a large range of possible futures for the Arctic under scenarios of continuing emissions of GHGs and other pollutants. For practical reasons, only a limited number of future change scenarios could be developed for this assessment. Nonetheless, while the ACIA used only two different emissions scenarios, five global climate models were used to project change under the two emissions scenarios, capturing a good range of the uncertainty associated with how different models represent climate system processes.
Fig.
18.4. Changes in surface air temperature north of 60º N between the
1981–2000 baseline and 2100 as projected by the five ACIA-designated
models forced with the A2 and B2 emissions scenarios.
Under the A2 and B2 emissions scenarios, the models projected that mean annual arctic surface temperatures north of 60º N will be 2 to 4 ºC higher by mid-century and 4 to 7 ºC higher toward the end of the 21st century (Fig. 18.4), compared to the present. Precipitation is projected to increase by about 8% by mid-century and by about 20% toward the end of the 21st century. There are differences among the projections from the different models, however. Although the projected trends are similar for the next few decades, the scatter of results for either the A2 or B2 emissions scenarios is about 2 to 3 ºC toward the end of the 21st century. The reasons for this scatter are differences in the representation of physical processes and feedbacks that are particularly important in the Arctic (e.g., changes in albedo due to reduced snow and ice cover, clouds, atmosphere– ocean interactions, ocean circulation), and natural variations that remain significant compared with the induced changes for at least the next few decades.While observations seem to indicate some increase in the frequency and severity of extreme events, these are very difficult to project.
Composite five-model projections for annual and winter mean surface air temperature changes in the Arctic between 1981–2000 and 2071–2090 using the B2 emissions scenario are shown in Fig. 18.5a (annual) and Fig. 18.5b (winter). Projected annual temperatures show a fairly uniform warming of 2 to 4 ºC throughout the Arctic by the end of the century, with a slightly higher warming of up to 5 ºC in the East Siberian Sea. Summer temperatures are projected to increase by 1 to 2 ºC over land, with little change in the central Arctic Ocean, where sea ice melts each summer, keeping the ocean temperature close to 0 ºC.Winter temperatures show the greatest warming: about 5 ºC over land, and up to 8 to 9 ºC in the central Arctic Ocean, where the feedback due to reduced sea-ice extent is largest. Regional and seasonal differences between the individual model results can be large, however, for the reasons previously discussed.
Fig.
18.5. (a) Projected annual surface air temperature change from the
1990s to the 2090s, based on the average change projected by the five
ACIA-designated climate models using the B2 emissions scenario. (b)
Projected surface air temperature change in winter from the 1990s to the
2090s, based on the average change projected by the five
ACIA-designated climate models using the B2 emissions scenario.
Changes in the Arctic affect the global system in several ways. Global climate change is influenced by feedback processes operating in the Arctic; these also amplify climate change in the Arctic itself. Apart from the well known and often quoted ice- and snow-albedo feedback, another important arctic feedback is the thawing of permafrost, which is likely to lead to additional GHG releases. Arctic cloud feedbacks are also important but are still poorly understood. Some of these arctic feedbacks are adequately represented in general circulation models while others are not. Changes in the Arctic also affect the global system in other ways. Climate change is likely to increase precipitation throughout the Arctic and increase runoff to the Arctic Ocean; such a freshening is likely to slow the global thermohaline circulation with consequences for global climate. The melting of arctic glaciers and ice sheets is another effect of climate change that contributes to global sea-level rise with all its inherent problems. The global implications of these feedbacks are discussed in greater detail in section 18.2.2.
Atmospheric ozone is vital to life on earth. The stratosphere contains the majority of atmospheric ozone, which shields the biosphere by absorbing UV radiation from the sun. Anthropogenic chlorofluorocarbons are primarily responsible for the depletion of ozone in the stratosphere, particularly over the poles. Atmospheric dynamics and circulation strongly influence ozone amounts over the poles, which in normal conditions tend to be higher than over other regions on earth. During conditions of ozone depletion, however, ozone over the polar regions can be substantially reduced. This depletion is most severe in the late winter and early spring, when unperturbed ozone amounts are typically high. Ozone losses over the Arctic are also strongly influenced by meteorological variability and large-scale dynamical processes.Winter temperatures in the polar stratosphere tend to be near the threshold temperature for forming polar stratospheric clouds, which can accelerate ozone destruction, leading to significant and long-lasting depletion events. Because climate changes due to increasing GHGs are likely to lead to a cooling of the stratosphere, polar stratospheric cloud formation is likely to become more frequent in future years, causing episodes of severe ozone depletion to continue to occur over the Arctic.
Decreases in stratospheric ozone concentrations are very likely to lead to increased UV radiation levels at the surface of the earth. Clouds, aerosols, surface albedo, altitude, and other factors also influence the amount of UV radiation reaching the surface. Achieving an accurate picture of UV radiation doses in the Arctic is complicated by low solar elevations and by reflectance off snow and ice. Ultraviolet radiation has long been a concern in the Arctic, as indicated by protective goggles found in the archaeological remains of indigenous peoples. Depletion of ozone over the Arctic, as has been observed in several years since the early 1980s, can lead to increased amounts of UV radiation, particularly UV-B radiation, reaching the surface of the earth, exposing humans and ecosystems to higher doses than have historically been observed. These higher doses are most likely to occur during spring, which is also the time of year when many organisms produce their young and when plants experience new growth. Because ecosystems are particularly vulnerable to UV radiation effects during these stages, increased UV radiation doses during spring could have serious implications throughout the Arctic.
Chapter 5 discusses observed and projected changes in atmospheric ozone and surface UV radiation levels. Satellite and ground-based observations since the early 1980s indicate substantial reductions in ozone over the Arctic during the late winter and early spring. Between 1979 and 2000, mean spring and annual atmospheric ozone levels over the Arctic declined by 11 and 7%, respectively. During the most severe depletion events, arctic ozone losses of up to 45% have occurred. Although international adherence to the Montreal Protocol and its amendments is starting to lead to a decline in the atmospheric concentrations of ozone depleting substances, ozone levels over the Arctic are likely to remain depleted for the next several decades. For the Arctic, most models project little recovery over the next two decades. Episodes of very low spring ozone levels are likely to continue to occur, perhaps with increasing frequency and severity because of the stratospheric cooling projected to result from increasing concentrations of GHGs. These episodes of very low ozone can allow more UV radiation to reach the earth’s surface, suggesting that people and ecosystems in the Arctic are likely to be exposed to higher-than-normal UV radiation doses for perhaps the next 50 years.
Table 18.2 summarizes some of the major aspects of changes in ozone and UV radiation levels.
Table 18.2. Observed and projected trends in ozone and ultraviolet radiation levels and factors affecting levels of ultraviolet radiation in the Arctic. This table is mainly based on Chapter 5.
| Observed | Projected | |
| Ozone and UV radiation trends | Combined satellite and ground-based observations indicate that mean spring and annual atmospheric ozone levels over the Arctic declined by 11 and 7%, respectively, between 1979 and 2000.These losses allowed more UV radiation to reach the surface of the earth. Individual measurements suggest localized increases in surface UV radiation levels, although high natural variability makes it difficult to identify a trend conclusively. | Future ozone levels over the Arctic are difficult to project, partly owing to the link with climate change. Current projections suggest that ozone over the Arctic is likely to remain depleted for several decades.This depletion would allow UV radiation levels to remain elevated for several decades.The elevated levels are likely to be most pronounced in spring, when many ecosystems are most sensitive to UV radiation exposure. |
| Low ozone episodes | Multi-week episodes of very low ozone concentration (depletion of 25 to 45%) have been observed in several springs since the early 1990s. | Decreasing stratospheric temperatures resulting from climate change may cause low ozone episodes to become more frequent. |
| Seasonal variations in ozone and UV radiation levels | There is high seasonal and interannual variability in arctic ozone levels, due to atmospheric processes that influence ozone production and distribution. Over the Arctic, stratospheric ozone levels are typically highest in late winter and early spring, when ozone depletion is most likely to occur. Surface UV radiation amounts vary with solar angle and day length throughout the year. In general, UV radiation doses are highest in summer, but can also be significant in spring due to ozone depletion combined with UV radiation enhancements from reflection off snow. | |
| Cloud effects | Cloud cover typically attenuates the amount of UV radiation reaching the surface of the earth. When the ground is snow-covered, this attenuation is diminished and UV radiation levels reaching the surface may increase due to multiple scattering between the surface and cloud base. | Future changes in cloud cover are currently difficult to project, but are likely to be highly regional. |
| Albedo effects | Changes in snow and ice extent affect the amount of UV radiation reflected by the surface. Reflection off snow can increase biologically effective UV irradiance by over 50%. In addition, high surface albedo affects UV radiation amounts incident on vertical surfaces more strongly than amounts incident on horizontal surfaces. Snow-covered terrain can substantially enhance UV radiation exposure to the face or eyes, increasing cases of snow blindness and causing potential long-term skin or eye damage. | Climate changes are likely to alter snow cover and extent in the Arctic. Reduced snow and ice cover means less reflection of UV radiation, decreasing the UV radiation levels affecting organisms above the snow. |
| Snow and ice cover | Snow and ice cover shields many arctic ecosystems from UV radiation for much of the year. | Climate changes are likely to alter snow cover and extent in the Arctic. Reduced snow and ice cover will increase the UV radiation levels experienced by organisms that would otherwise be shielded by snow or ice cover. |
| Impacts of increased UV radiation levels | Ultraviolet radiation effects on organisms in human health and on terrestrial and aquatic ecosystems include skin cancer, corneal damage, immune suppression, sunburn, snow blindness. Ultraviolet radiation also damages wood, plastics, and other materials widely used in arctic infrastructure. | All the impacts noted in the “Observed” column are likely to worsen. |
Changes in snow, ice, and permafrost
Recent observational data, discussed in detail in Chapter 6, present a generally consistent picture of cryospheric variations that are shaped by patterns of recent warming and variations in atmospheric circulation. Consistent with the overall increase in global temperatures, arctic snow and ice features have diminished in extent and volume. While the various cryospheric and atmospheric changes are consistent in an aggregate sense and are quite large in some cases, it is possible that natural, low frequency variations in the atmosphere and ocean have played at least some role in forcing the cryospheric and hydrological trends of the past few decades.
Model projections of anthropogenic climate change indicate a continuation of the recent trends through the 21st century, although the rates of the projected changes vary widely due to differences in model representations of feedback processes. Models project a 21stcentury decrease in sea-ice extent of up to 100% in summer; a widespread decrease in snow-cover extent, particularly in spring and autumn; and permafrost degradation over 10 to 20% of the present permafrost
area and a movement of the permafrost boundary northward by several hundred kilometers. The models also project river discharge increases of 5 to 25%; earlier breakup and later freeze-up of rivers and lakes; and a sea-level rise of several tens of centimeters resulting from glacier melting and thermal expansion, which is amplified or reduced in some areas due to long-term land subsidence or uplift.
Table 18.3 summarizes observed and projected trends in the snow and ice features of the Arctic, including snow cover, glaciers, permafrost, sea ice, and sea-level rise. Because the snow and ice features of the Arctic are not only sensitive indicators of climate change but also play a crucial role in shaping the arctic environment, any changes in these features are very likely to have profound effects on the environment, biota, ecosystems, and humans.
Changes on land
Climate change is also likely to have profound effects on the tundra and boreal forest ecosystems of the Arctic. Arctic plants, animals, and microorganisms adapted to climate change in the past primarily by relocation, and their main response to future climate change is also likely to be relocation. In many areas of the Arctic, however, relocation possibilities are likely to be limited by regional and geographical barriers. Nevertheless, changes are already occurring in response to recent warming. Chapters 7, 8, and 14 provide details of the major conclusions presented here.
Some arctic species, especially those that are adapted to the cold arctic environment (e.g., mosses, lichens, and some herbivores and their predators) are especially at risk of loss in general, or displacement from their present locations. Present species diversity is more at risk in some ACIA regions than others; for example, Beringia (Region 3) has a higher number of threatened plant and animal species than any other ACIA region.While there will be some losses in many arctic areas, movement of species into the Arctic is likely to cause the overall number of species and their productivity to increase, thus overall biodiversity measured as species richness is likely to increase along with major changes at the ecosystem level.
Table 18.3. Observed and projected trends for the arctic cryosphere. This table is mainly based on Chapter 6.
| Observed | Projected for the 21st century | |
| Snow cover | Snow-cover extent in the Northern Hemisphere has decreased by 5 to 10% since 1972; trends of such magnitude are rare in GCM simulations. | Snow-cover extent is projected to decrease by about 13% by 2071–2090 under the projected increase in mean annual temperature of about 4 ºC. The projected reduction is greater in spring. Owing to warmer conditions, some winter precipitation in the form of rain is likely to increase the probability of ice layers over terrestrial vegetation. |
| Glaciers | Glaciers throughout the Northern Hemisphere have shrunk dramatically over the past few decades, contributing about 0.15 to 0.30 mm/yr to the average rate of sea-level rise in the 1990s. | The loss of glacial mass through melting is very likely to accelerate throughout the Arctic, with the Greenland Ice Sheet also starting to melt. These changes will tend to increase the rate of sea-level rise. |
| Permafrost | Permafrost temperatures in most of the Arctic and subarctic have increased by several tenths of a degree to as much as 2 to 3 ºC (depending on location) since the early 1970s. Permafrost thawing has accompanied the warming. | Over the 21st century, permafrost degradation is likely to occur over 10 to 20% of the present permafrost area, and the southern limit of permafrost is likely to move northward by several hundred kilometers. |
| Sea ice | Summer sea-ice extent decreased by about 7% per decade between 1972 and 2002, and by 9% per decade between 1979 and 2002, reaching record low levels in 2002.The extent of multi-year sea ice has also decreased, and ice thickness in the Arctic Basin has decreased by up to 40% since the 1950s and 1960s due to climate-related and other factors | Sea-ice extent is very likely to continue to decrease, particularly in summer. Model projections of summer sea-ice extent range from a loss of several percent to complete loss.As a result, the navigation season is projected to be extended by several months. |
| River discharge | River discharge has increased over much of the Arctic during the past few decades and the spring discharge pulse is occurring earlier. | Models project that total river discharge is likely to increase by an additional 5 to 25% by the late 21st century. |
| Breakup and freeze-up | Earlier breakup and later freeze-up of rivers and lakes across much of the Arctic have lengthened the ice-free season by 1 to 3 weeks. |
The trend toward earlier breakup and later freeze-up of rivers and lakes is very likely to continue, consistent with increasing temperature. Breakup flooding is likely to be less severe. |
| Sea-level rise | Global average sea level rose between 10 and 20 cm during the 20th century.This change was amplified or moderated in particular regions by tectonic motion or isostatic rebound. | Models project that glacier contributions to sealevel rise will accelerate in the 21st century. Combined with the effects of thermal expansion, sea level is likely to rise by 20 to 70 cm (an average of 2 to 7 mm/year) by the end of the 21st century. |
Freshwater systems in the Arctic will also be affected due to changes in river runoff, including the timing of runoff from thawing permafrost, and changes in river-and lake-ice regimes. Changes in water flows as permafrost thaws are very likely to alter the biogeochemistry of many areas and create new wetlands and ponds, connected by new drainage networks. More water will alter the winter habitats in freshwater systems and increase survival of freshwater and sea-run fish. On hill slopes and higher ground, permafrost thawing is likely to drain and dry existing soils and wetlands. The productivity of these systems is likely to increase, as well as species diversity.
Changes in animal and plant populations are often triggered by extreme events, particularly winter processes. Weather extremes in winter are likely to have greater effects on the mammals and birds that remain active in winter, than on plants, insects, and other invertebrates that are dormant in winter.While some projections indicate a likely increase in the frequency and severity of extreme events (storms, floods, icing of snow layers, drought) the distribution of these events is very difficult to project. Rapid changes present additional stresses if they exceed the ability of species to adapt or relocate since they are likely to lead to increased incidence of fires, disease, and insect outbreaks, as well as to restricted forage availability.
The impact of changes in climate and UV radiation levels on species and ecosystems is likely to make the current use of many protected areas as a conservation practice almost obsolete. Although local measures to reduce hunting quotas might moderate impacts of climate change on wildlife species, habitat protection requires a new, more flexible paradigm. Comparison of areas in the Arctic in which vegetation is likely to dramatically change with the location of current protected areas shows that many habitats will be altered so that they will no longer serve to support the intended species or communities. These impacts will be reduced if simple measures are incorporated into the design of protected areas, for example, designating flexible boundaries that encompass extended latitudinal tracts of land and protect corridors for species movement.
As warming allows trees to grow, forests are projected to replace a significant proportion of the tundra.
This process is very likely to be slowed locally by natural barriers to movement, human activities, fires, insect attacks, browsing by vertebrate herbivores, and drying or water logging of soils, but the long-term effect on species composition will be significant. Displacement of tundra by forest will also lead to a decrease in albedo, which will increase the positive (warming) feedback to the climate system, especially during spring when snow melts, and amplify changes in the local climate.Warming and drying of tundra soils are likely to lead to an increased release of carbon, at least in the short term. However, current models suggest that the Arctic may become a net sink for carbon (although the uncertainties associated with the projections are high). There are also uncertainties about changes in methane (CH4) fluxes (although current CH4 emissions from arctic ecosystems are already forcing climate) from wetlands, permafrost, and CH4 hydrates, so it is not known if the circumpolar tundra will become a carbon sink or carbon source in the long term.
Tables 18.4 and 18.5 summarize the most important impacts projected for terrestrial and freshwater ecosystems, respectively.
Table 18.4. Projected impacts on terrestrial ecosystems. This table is mainly based on Chapter 7.
| Projected impact | |
| Ecotone transition | Warming is very likely to lead to slow northward displacement of tundra by forests, while tundra will in turn displace high-arctic polar desert.Tundra is projected to decrease to its smallest extent in the last 21000 years. In dry areas where thawing permafrost leads to drainage of the active layer, forests are likely to be replaced by tundra– steppe communities.Where thawing permafrost leads to waterlogging, forest will be displaced by bogs and wetlands. |
| Forest changes | Forests are likely to expand and in some areas, where present-day tundra occupies a narrow zone, are likely to reach the northern coastline.The expansion will be slowed by increased fire frequency, insect outbreaks, and vertebrate herbivory, as has already been observed in some parts of the Arctic. |
| Species diversity | Climate warming is very likely to lead to northward extension of the distribution ranges of species currently present in the Arctic and to an increase in the total number of species. Individual species will move at different rates and new communities of associated species are likely to form. Climate warming is also likely to lead to a decline or extirpation of populations of arctic species at their southern range margins.As additional species move in from warmer regions, the number of species in the Arctic and their productivity are very likely to increase. |
| Species at risk | Specialist species adapted to the cold arctic climate, ranging from mosses, lichens, vascular plants, some herbivores (lemmings and voles) and their predators, to ungulates (caribou and reindeer), are at risk of marked population decline or extirpation locally.This will be largely as a consequence of their inability to compete with species invading from the south.The biodiversity in Beringia is at risk as climate warms since it presently has a higher number of threatened plant and animal species than any other arctic region. |
| UV radiation effects |
Increased UV radiation levels resulting from ozone depletion are likely to have both short- and long-term impacts on some ecosystem processes, including reduced nutrient cycling and decreased overall productivity. Many arctic plant species are assumed to be adaptable to high levels of UV-B radiation.Adaptation involves structural and chemical changes that can affect herbivores, decomposition, nutrient cycling, and productivity. |
| Carbon storage and fluxes | Over the long term, replacement of arctic vegetation with more productive southern vegetation is likely to increase net carbon storage in ecosystems, particularly in regions that are now tundra or high-arctic polar desert. Methane fluxes are likely to increase as vegetation grows in tundra ponds, and as wetlands become warmer (until they dry out). Methane fluxes are also likely to increase when permafrost thaws. |
| Albedo feedback | The positive feedback of albedo change (due to forest expansion) on climate is likely to dominate over the negative (cooling) feedback from an increase in carbon storage.The albedo reduction due to reduced terrestrial snow cover will be a major additional feedback. |
Table 18.5. Projected impacts on freshwater ecosystems. This table is mainly based on Chapter 8.
| Projected impact | |
| Lakes | Reduced ice cover and a longer open-water season are very likely to affect thermal regimes, particularly lake stratification. Permafrost thaw in ice-rich environments is very likely to lead to catastrophic lake drainage; increased groundwater flux will drain other lakes.A probable decrease in summer water levels of lakes and rivers is very likely to affect the quality and quantity of, and access to, aquatic habitats. |
| Rivers | A likely shift to less intense ice breakup will reduce the ability of flow systems to replenish riparian ecosystems, particularly in river deltas. Reduced climatic gradients along large northern rivers are likely to alter ice-flooding regimes and related ecological processes.A very likely increase in winter flows and reduced ice-cover growth will increase the availability of under-ice habitats. |
| Water quality | Enhanced permafrost thawing is very likely to increase nutrient, sediment, and carbon loadings to aquatic systems, with a mixture of positive and negative effects on freshwater chemistry.An earlier phase of enhanced sediment supply will probably be detrimental to benthic fauna but the balance will be ecosystem- or site-specific. Freshwater biogeochemistry is very likely to alter following changes in water budgets. |
| Wetlands | Changes in climate are very likely to lead to an increased extent of wetlands, ponds, and drainage networks in low-lying permafrost-dominated areas, but also to losses of wetlands on hill slopes and higher ground. Coastal erosion and inundation will generate new wetlands in some coastal areas. Conversely, increased evapotranspiration is likely to dry peatlands, particularly during the warm season. |
| Species diversity | Changes in the timing of freshwater habitat availability, quality, and suitability are very likely to alter the reproductive success of species. Correspondingly, the rate and magnitude of climate change and its effects on aquatic systems are likely to outstrip the capacity of many aquatic biota to adapt or acclimate. Climate change is very likely to act cumulatively and/or synergistically with other stressors to affect the overall biodiversity of aquatic ecosystems. |
| UV radiation effects | Reduced ice cover in freshwater ecosystems is likely to have a greater effect on underwater UV radiation exposure than projected levels of stratospheric ozone depletion. Little is known about the adaptive responses of aquatic organisms to changing UV radiation levels. |
Changes in the ocean
Through its influence on the Atlantic thermohaline circulation, the Arctic plays a critical part in driving the global thermohaline circulation. It is possible that increased precipitation and runoff of fresh water and the melting of glaciers and ice sheets, and thawing of the extensive permafrost underlying northern Siberia, could freshen arctic waters, causing a reduction in the overturning circulation of the global ocean and thus affecting the global climate system and marine ecosystems. The IPCC 2001 assessment considers a future reduction of the Atlantic thermohaline circulation as likely, while a complete shutdown is considered as less likely, but not impossible. If half the oceanic heat flux were to disappear with a weakened Atlantic inflow, then the associated cooling would more than offset the projected heating in the 21st century. Thus, there is the possibility that some areas in the Atlantic Arctic will experience significant regional cooling rather than warming, but the present models can assess neither its probability, nor its extent and magnitude.
The most important projected trends for the marine systems of the Arctic are summarized in Table 18.6.
Table 18.6. Projected impacts in the Arctic Ocean and subarctic seas. This table is mainly based on Chapters 9 and 13.
| Projected impact | |
| Ocean regime | Increased runoff from major arctic rivers and increased precipitation over the Arctic Ocean are very likely to decrease its salinity. |
| Thermohaline circulation |
A slow-down of the global thermohaline circulation is likely as a result of increased freshwater input from melting glaciers and precipitation.This is likely to delay warming for several decades in the Atlantic sector of the Arctic as a result of reduced ocean heat transport. |
| Sea-ice regime | All the ACIA-designated models project substantial reductions in sea-ice extent and likely opening of the Northern Sea Route to shipping during summer. Some of the models project an entirely ice-free Arctic Ocean in summer by the end of the 21st century. Greater expanses of open water will also increase the positive feedback of albedo change to climate. |
| Marine ecosystems |
Reduced sea-ice extent and more open water are very likely to change the distribution of marine mammals (particularly polar bears, walrus, ice-inhabiting seals, and narwhals) and some seabirds (particularly ivory gulls), reducing their populations to vulnerable low levels. It is likely that more open water will be favorable for some whale species and that the distribution range of these species is very likely to spread northward. |
| UV radiation effects |
Ultraviolet radiation can act in combination with other stressors, including pollutants, habitat destruction, and changing predator populations, to adversely affect a number of aquatic species. In optically clear ocean waters, organisms living near the surface are likely to receive harmful doses of UV radiation. Sustained, increased UV radiation exposure could also have negative impacts on fisheries. |
| Fisheries | Changes in the distribution and migration patterns of fish stocks are likely. It is possible that higher primary productivity, increases in feeding areas, and higher growth rates could lead to more productive fisheries in some regions of the Arctic. New species are moving into the Arctic and competing with native species.The extinction of existing arctic fish species is unlikely. |
| Coastal regions | Serious coastal erosion problems are already evident in some low-lying coastal areas, especially in the Russian Far East, Alaska, and northwestern Canada, resulting from permafrost thawing and increased wave action and storm surges due to reduced sea-ice extent and sea-level rise. Ongoing or accelerated coastal-erosion trends are likely to lead to further relocations of coastal communities in the Arctic. |
Several chapters address the impacts of climate change on people, including Chapters 10, 11, 12, 14, 15, and 16. The Arctic is home to a large number of distinct groups of indigenous peoples and the populations of eight nations. Between two and four million indigenous and non-indigenous people live in the Arctic, depending on how the Arctic is defined. Most live in cities; in Russia large urban centers include Vorkuta and Norilsk with populations listed as exceeding 100000, and Murmansk with about 500000 people, although the population of these cities has decreased in recent years. Arctic towns in Scandinavia and North America are smaller; Reykjavik has around 110000 inhabitants and Rovaniemi about 65000. In total there are probably around 30 towns in the Arctic with more than 10 000 inhabitants.
Table 18.7 summarizes the projected social impacts of climate change and UV radiation on the people of the Arctic. Climate change is only one, and perhaps not the most important, factor currently affecting people’s lives and livelihood in the Arctic. For example, the people living in Russia’s Far North have experienced dramatic political, social, and economic changes since the collapse of the former Soviet Union; and Europeans, Canadians, and Alaskans have experienced major changes resulting from the discovery of minerals, oil and gas reserves, and the declines or increases of some of the northern fisheries.
Table 18.7. Projected social impacts on arctic residents.This table is mainly based on Chapters 12, 15, and 16.
| Projected impact | |
| Impacts on arctic residents | |
| Infrastructure | Permafrost thawing is very likely to threaten buildings, roads, and other infrastructure.This includes increases in the settling and breaking of underground pipes and other installations used for water supply, heating systems, and waste disposal, and threats to the integrity of containment structures such as tailing ponds and sewage lagoons. |
| Water | While increased river runoff is projected to occur mainly in winter and spring, lower water tables in rivers and lakes in summer will reduce available water and impede river travel in some areas (e.g., the Mackenzie River watershed). |
| Health | Circumpolar health problems such as those associated with changes in diet and UV radiation levels are likely to become more prominent. Increases in zoonotic diseases and injury rates are likely, due to environmental changes and climate variability. |
| Income | Impacts on the economy are expected as a consequence of climate change in the Arctic and will affect work opportunities and income of arctic residents. Expected increases in productivity and greater opportunity for settlement are also likely to benefit people within and beyond the region. |
| Impacts specific to indigenous communities | |
| Food security | Obtaining and sharing traditional foods, both cultural traditions, are very likely to become more difficult as the climate changes, because access to some food species will be reduced.The consequences of shifting to a moreWestern diet are likely to include increased incidence of diabetes, obesity, and cardiovascular diseases. Food from other sources may also be more costly. |
| Hunting | Hunter mobility and safety and the ability to move with changing distribution of resources, particularly on sea ice, are likely to decrease, leading to less hunting success. Similarly, access to caribou by hunters following changed snow and river-ice conditions is likely to become more difficult. Harvesting the threatened remaining populations of some marine mammals could accelerate their demise. |
| Herding | Changing snow conditions are very likely to adversely affect reindeer and caribou herding (e.g., ice layers and premature thawing will make grazing and migration difficult and increase herd die-offs). Shorter duration of snow cover and a longer plant growth season, on the other hand, are likely to increase forage production and herd productivity if range lands and stocking levels are adequately managed. |
| Cultural loss | For many Inuit, climate change is very likely to disrupt or even destroy their hunting culture because sea-ice extent is very likely to be reduced and the animals they now hunt are likely to decline in numbers, making them less accessible, or they may even disappear from some regions. Cultural adaptation to make use of newly introduced species may occur in some areas. |
For the indigenous population, and particularly for those people who depend on hunting, herding, and fishing for a living, climate change is likely to be a matter of cultural survival, however. Their uniqueness as people with cultures based on harvesting marine mammals, hunting, herding caribou and reindeer, or fishing, is at risk because climate change is likely to deprive them of access to their traditional food sources, although new species, as they move north, may become available in some regions. Indigenous peoples have adapted to changes in the past through careful observations and skillful adjustments of their traditional activities and lifestyles, but the addition of climate and UV radiation changes and impacts on existing social, political, and other environmental stresses is already posing serious challenges. Today, the indigenous peoples live in greatly circumscribed social and economic situations and their hunting and herding activities are determined to a large extent by resource management regimes and local, regional, and global economic market situations that reduce their ability to adapt and cope with climate variability and change.While they experience stress from other sources that threatens their lifestyles and cultures, climate change magnifies these threats.
Improvements in human health are very likely to continue through advances in technology, but the potential for emerging diseases (via the introduction of new insect and animal vectors) in northern communities makes it difficult to project how climate change is likely to affect the overall health of arctic residents. Several types of impacts seem likely. Because it will be more difficult to access marine animals when hunting, and because there is greater danger to the hunters when traveling over thinner sea ice, and in open water in less predictable weather conditions, direct health effects through a changing diet and increased accident rates are likely. Increased UV radiation levels are also likely to directly affect health, increasing incidences of skin cancer, cataracts, and viral infections, owing to effects on the immune system. Studies by the World Health Organization estimate that a person receives the majority of their lifetime UV radiation exposure before 18 years of age. An entire generation of people in the Arctic is likely to continue to be exposed to above normal UV radiation levels, and a new generation will grow to adulthood under increased UV radiation levels. Although behavioral adaptations can reduce the expected impacts, adequate information and education about these effects must be available.
Table 18.8. Projected impacts on important economic activities in the Arctic. This table is mainly based on Chapters 13, 14, and 16, but also draws information from other chapters.
| Projected impact | |
| Non-renewable resources | |
| Oil and gas | |
| Exploration | Reduced sea ice is likely to facilitate some offshore operations but hamper winter seismic work on shore-fast ice. Later freeze-up and earlier melting are likely to limit the use of ice and snow roads. |
| Production | Reduced extent and thinner sea ice are likely to allow construction and operation of more economical offshore platforms. Storm surges and sea-level rise are likely to increase coastal erosion of shore facilities and artificial islands.The costs of maintaining infrastructure and minimizing environmental impacts are likely to increase as a result of thawing permafrost, storm surges, and erosion. |
| Transportation | Reduced extent and duration of sea and river ice are likely to lengthen the shipping season and shorten routes (including trans-polar routes). Permafrost thawing is likely to increase pipeline maintenance costs. |
| Coal and minerals | |
| Production | The costs of maintaining infrastructure and minimizing environmental impacts are likely to increase as a result of thawing permafrost, storm surges, and erosion. |
| Transportation | Reduced extent and duration of sea ice are likely to lengthen the shipping season.Thawing permafrost is likely to affect roads and infrastructure. |
| Renewable resources | |
| Fish, shellfish, freshwater fish | |
| Fish stock | Temperature, currents, and salinity changes are likely to lead to changes in species availability (positive in some areas, negative in others). |
| Harvests | Changes in migration patterns are likely to lead to changes in distances to fishing grounds, and possible relocation of processing plants. Increased storms, and icing of ship superstructure are likely to increase risks and reduce catches. |
| Timber | Productivity is likely to increase if there is adequate soil moisture but decrease if there are summer droughts. Fire and insect outbreaks are likely to decrease productivity. |
| Agricultural products | A warmer climate is likely to lengthen the growing season and extend the northern range of agriculture. Increased insect problems are likely to decrease productivity. |
| Energy | |
| Hydropower | Precipitation changes are likely to affect the water supply. Melting glaciers are likely to reduce future seasonal water supply. |
| Power lines | Icing events, storms, and ground thaw are likely to affect power lines. |
| Wildlife | |
| Harvests | Changes in distribution and migration patterns are likely to affect access to wildlife and change harvests. Invasive species are likely to compete with existing populations. |
| Conservation | Habitat loss, longer seasons, and boat access are likely to lead to over-harvesting in protected areas and affect conservation. |
The three most important sectors of the commercial economy of the Arctic are oil and gas, fish, and minerals, each of which will be influenced by changes in the climate. There are also other economic sectors that will be affected by climate change, including forestry, agriculture, and tourism. Impacts on industry and commerce are described in greater detail in Chapters 13, 14, and 16. The use of local resources for traditional purposes, including fish, wildlife, plants, and wood for fuel and home construction, are also part of the arctic economy and have been addressed in Chapters 11, 12, and 17.
Oil and gas
The Arctic has large oil and gas reserves. Most are located in Russia: oil in the Pechora Basin, gas in the Lower Ob Basin, and other potential oil and gas fields along the Siberian coast. In Siberia, oil and gas development has expanded dramatically over the past few decades, and this region produces 78% of Russia’s oil and 84% of its natural gas. Canadian oil and gas fields are concentrated in two main basins in the Mackenzie Delta/Beaufort Sea region and in the high Arctic. Oil and gas fields also occur in other arctic waters, for example the Barents Sea. The oil fields at Prudhoe Bay, Alaska, are the largest in North America, and by 2002, around 14 billion barrels had been produced at this site. There are also substantial reserves of natural gas and coal along the North Slope of Alaska. The Arctic is an important supplier of oil and gas to the global economy. Climate change impacts on the exploration, production, and transportation activities of this industry could have both positive and negative market and financial effects. These are summarized in Table 18.8.
Fish
The arctic seas contain some of the world’s oldest and most productive commercial fishing grounds. In the Northeast Atlantic and the Bering Sea and Aleutian region, annual fish harvests in the past have exceeded two million tonnes in each of the two regions. In the Bering Sea, overall harvests have remained stable at about two million tonnes, but while some species like pollock (Theragra chalcogramma) are doing well, others like snow crab (Chionoecetes opilio) have declined. Important fisheries also exist around Iceland, Greenland, the Faroe Islands, and Canada. Fisheries are important to many arctic countries, as well as to the world as a whole. For example, Norway is one of the world’s biggest fish exporters with exports worth US$ 4 billion in 2001. In some arctic regions aquaculture is a growing industry, providing local communities with jobs and income. Freshwater fisheries are also important in some areas. Changes in climatic conditions are likely to have both positive and negative financial impacts (see Table 18.8).
Minerals
The Arctic has large mineral reserves, ranging from gemstones to fertilizers. Russia extracts the greatest quantities of these minerals, including nickel, copper, platinum, apatite, tin, diamonds, and gold, mostly on the Kola Peninsula but also in the northern Ural Mountains, the Taymir region of Siberia, and the Far East. Canadian mining in the Yukon and Northwest Territories and Nunavut is for lead, zinc, copper, gold, and diamonds. In Alaska, lead and zinc are extracted at the Red Dog Mine, which sits atop two-thirds of US zinc resources, and gold mining continues in several areas. Coal mining occurs in several areas of the Arctic. Mining activities in the Arctic are an important contributor of raw materials to the global economy and are likely to expand with improving transportation conditions to bring products to market, due to a longer ice-free shipping season (Table 18.8).
Transportation industry
The cost of transporting products and goods into and out of the Arctic is a major theme of the potential impacts of climate change on many of the economic sectors described above.While climate change will affect many different modes of transport in the Arctic, the likelihood of reduced extent and duration of sea ice in the future will have a major impact. The projected opening of the Northern Sea Route (the opening of the Northwest Passage is less certain) to longer shipping seasons (Chapter 16) will provide faster and therefore cheaper access to the Arctic, as well as the possibility of trans-arctic shipping. This will provide new economic opportunities, as well as increased risks of oil and other pollution along these routes. Other regions of the Arctic will also benefit from easier shipping access due to less sea ice.
Projected climate-related impacts on the major economic sectors in the Arctic are listed in Table 18.8. This is a qualitative assessment only, since detailed financial estimates of economic impacts are not available at present, except in very few instances. Over the 21st century, new types of activities could arise (for example trans-arctic shipping) but there are likely to be others. This analysis focuses on how future climate change could affect the present economy, and is not based on projections of economic and demographic development in the Arctic over the 21st century.
Forestry, agriculture, and tourism
Forestry is an important economic activity in six of the eight arctic countries, and agriculture in its various forms also contributes to local economies in all eight countries. The basis for agricultural activities varies throughout the Arctic. In North America, the limited agriculture helps to meet the need for local fresh produce during the short summer. In northern Europe and across the Russian North, crop production along with reindeer husbandry and some other domestic livestock production serve traditional cultural needs and provide opportunities for income. Tourism is also becoming an increasingly important economic factor in many arctic regions. Impacts on these economic sectors in monetary terms are difficult to project and quantify since factors other than climate, including future regional economic development, play a major role.
Wildlife
Arctic wildlife resources support communities throughout the Arctic, through whaling, fishing, and hunting, and wildlife contributes to both the monetary and traditional economies of the Arctic. Climate change threatens the culture and traditional lifestyles of indigenous communities but is not discussed here. Likely economic impacts due to climate change are relevant here but are not easily quantified at present.
Chapter 18: Summary and Synthesis of the ACIA
18.1. Introduction
18.2. A summary of ACIA conclusions
18.3. A synthesis of projected impacts in the four regions
18.4. Cross-cutting issues in the Arctic
18.5. Improving future assessments
18.6. Conclusions
References
NOTE:This chapter is a summary based on the seventeen preceding chapters of the Arctic Climate Impact Assessment and a full list of references is provided in those chapters. Only references to major publications and data sources, including integrative regional assessments, and some papers reporting the most recent developments, are listed.
- ^IPCC, 2001. Climate Change 2001: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, 1032p.
- ^Ibid
- ^ Nakisenovis, N. and R. Swart (eds.), 2000. Intergovernmental Panel on Climate Change, Special Report on Emissions Scenarios. Cambridge University Press, 599p.
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