5. Sumary and conclusions
The overall assumption of the most recent IPCC climate change report (Houghton et al. 1996) is that the on-going increase in atmospheric CO2 leads to atmospheric warming, most drastic at high latitudes. Arctic and sub-Arctic regions are predicted to experience greater warming than the global average, but Greenland may be an exception as a result of changes in thermohaline circulation in the North Atlantic sea and its generally more maritime climate than other High Arctic regions.
5.1 Climate change in Greenland
Climate change in Greenland is predicted to cause an increase in the mean yearly temperature of between 1.8-3.6°C by the end of the next century. The greatest increase is expected at mid- and high latitudes in West Greenland. The increase will primarily be an increase in winter temperatures. A slight diminution of the north-south temperature gradient is expected. The predicted maximum increase in July temperature is about +2°C for Ilulissat (Jakobshavn). The frequency of extreme low temperatures is expected to decrease. Warm extremes may occur more frequently both winter and summer.
The ice sheet will respond to warming through increased melt rates at the margins and accumulation rates in the interior. Melt rates will probably dominate. However, precipitation and melt rate predictions are not as reliable as temperature predictions.
Precipitation is predicted to increase by 2-24 mm/month, with most of the increase in the summer on the south and west coast, but in the winter or all year on the east coast and at high latitudes. Half the change will occur within the next 40-50 years. Other consequences of climate change include: lengthening of the snow-free season by a month or more, a slight increase in the length of the growing season by 1-2 weeks, a deepening of the soil active layer, and a shorter northward movement of the permafrost boundary.
There is considerable uncertainty regarding predictions for Southern Greenland, which has experienced a cooling of 1° -1.6°C in the past 60 years. Ocean models predict a cold centre SW of Greenland. The cooling effect around this centre will counteract and may even neutralize greenhouse warming in SE-Greenland. This cooling may be related to the 80% reduction in deep water formation observed in the Greenland Sea during the 1980s. Hence, less warm Atlantic water is streaming north. The max. temperature increase in South Greenland may, therefore, be a return to the mean summer temperatures of 60 years ago and the possibility of a temperature fall must be considered.
Depletion of the stratospheric ozone layer will continue in the first half of the next century, causing increased UV-B radiation, particularly towards the north, where the effect is increased by snow and ice albedo.
At sea, a decrease in the north-south gradient of sea surface temperatures is expected. Changes in sea level are still unclear, but in Greenland a world-wide increase in sea level will most likely be counterbalanced by a land raise. Reductions in sea ice thickness, surface area and duration are also expected.
5.1.1 Ecological implications
Long-term predictions of Arctic plant performance require a knowledge of the natural variation and dynamics in Greenland ecosystems, as well as a not yet available understanding of feedback mechanisms on e.g. element cycling and microclimate. Near future changes (10-20 years) are expected to be modest, particularly in the south, but later on, the following changes may occur where warming is expected.
188.8.131.52 Changes in patterns of terrestrial ecosystems
Initial changes at the population level in existing communities and ecosystems are expected to be followed by major changes in community structure, resulting in new types of dominant ecosystems. Disintegration of plant communities in the Arctic results in drastic changes for animal populations as well.
Lichens and mosses may become less frequent in heath and wetland ecosystems, and dwarf shrub and shrub vegetation may be favoured at the expense of grasses and herbs. Consequently, graminoid-dominated wetland may become restricted, causing a decline in plant species diversity and the abundance of grazing animals and their predators. Certain dwarf shrubs possess chemical defence against herbivores.
Evergreen perennial plants respond slowly or not at all with increased biomass and suffer a competitive disadvantage in communities with aggressive deciduous species, such as dwarf birch (Betula nana).
As the summer-winter temperature difference tends to decrease, coastal heath types, dominated by crowberry (Empetrum nigrum ssp. hermaphroditum), may expand in coastal regions.
Increased length of the growing season will cause present distribution boundaries for a number of plant species and vegetation types to move northward and to higher altitudes. A direct result of such a migration could be competitive exclusion of northern species by southern species. Animals will experience extended feeding areas and season in more productive high latitudes.
Where seed plants play a minor role in the High Arctic, lichens and mosses are expected to be the first to benefit from higher temperatures, as the existence of a dormant propagule bank is predicted. More dramatic changes are expected where colonizable bare ground exists, unless water supply is a limiting factor.
Arctic deserts, semi-deserts, and fellfields may be colonized by invading plants and animals, improving living conditions for man. Fast invasion of both barren and occupied areas may occur from existing, milder microhabitats. Species from outside such protected habitats are expected to move much more slowly.
Due to strong physical barriers, it is unlikely that Arctic plants can migrate fast enough to keep up with the speed of climate change. Eventually, however, immigration may lead to increased species diversity (decades, centuries).
If South Greenland becomes warmer, there may be a potential for small scale forestry and farming with highland cattle as the tree-line moves north and the risk of frost damage decreases in South Greenland. The northward migration of forest may be very slow, slower than in most other Arctic areas, because only a few copses exist in the southernmost, sub-Arctic Greenland. Migration rates for species of alder (Alnus) and birch (Betula) are about 130-1000 m per year.
A loss of species and biodiversity is predicted for the first many decades. Extreme changes in soil moisture and species competition may be direct causes, the latter influenced by nutrient availability, temperature, CO2, and UV-B.
Only a few High Arctic plants are in danger of being exterminated as a direct consequence of temperature increase. Ranunculus sabinei, which is today limited to the narrow outer coastal zone of North Greenland, has nowhere to go to avoid a warmer and drier climate. For individual species, plant or animal, temperature responses will be greatest closest to their climatic distributional limit.
Fossil evidence from the relatively warm Pleistocene shows, first, that High Arctic lowland fens can be restored from openings in boreal forest. Second, the occurrence of arctic species in Pleistocene remains indicates that although the tree-line and forest-tundra will move northward as warming proceeds, High Arctic ecosystems will not disappear from high latitudes with short growing seasons. In undisturbed fens, establishment of new plants is extremely slow.
Lichens, like Cladonia mitis, and some arctic mosses and higher plants are sensitive to UV-B radiation. The long-term changes, given an increasing UV-B irradiance trend in the Arctic, may be a reduction in cover and frequency. Interactions between increased CO2 and UV-B radiation may reduce the nutritional value of plants to herbivores. Data are lacking on UV-B as a threat to skin, vision and immune systems.
Arctic animals depend on stable winter climate with unbroken frost. Increasing snow depth and changed species composition of plant communities in the north may result in mass mortality of musk-ox and caribou. Rising winter temperatures could also be harmful to large herbivores, Arctic hares, and small rodents, such as lemmings, living beneath the snow cover. Repeated freezing and thawing results in ice-crust formation making it difficult to reach vegetation in winter. Herbivores may therefore experience periods of severe starvation. A decrease in herbivore populations will affect predators (fox and wolf) as well.
Increased snow cover, ice-crust formation and a prolonged thawing period will have a great impact on migratory birds, depending on the availability of insects or plants when they arrive in spring. If these food sources are not available in time, the birds will starve.
The size of insect populations are strongly controlled by temperature. The expected rise in winter temperature, therefore, may increase egg survival. Aphid populations, for example, may increase considerably.
Four of Greenland's five butterfly species are confined to the High Arctic or become more rare towards the south. They are expected to move north when warming occurs. Beetles depend on higher temperatures and may benefit from a warming and extend their range. Since insects are very sensitive to temperature changes, they could be useful as indicators of such changes.
184.108.40.206 Change in processes of terrestrial ecosystems
A drastic impact on vegetation is expected from permafrost melt, resulting in waterlogging or drought, depending on precipitation. As permafrost melts, there will be land subsidence (thermokarst erosion). This in turn leads to the formation of ponds and lakes. The changes in landscape, sea ice distribution, lake and river ice may not only have significant biological impacts, such as changes in caribou and polar bear migration routes, but would impact indigenous peoples as well.
An improved drainage effect may result due to thickening of the unfrozen zone between the seasonal frost and permafrost layers. A general drying-out of the soils will greatly affect wetland areas.
In areas subject to soil drying, herbivore productivity will be reduced. The absence of herbivores favours mosses, which act as an insulating layer over the soil, preserving water and slowing decomposition and nutrient cycling.
Where soils become wetter, lichens and mosses will play a more important role in ecosystem carbon fixation and control of water loss from the soil to the atmosphere. The largest effect may be seen where drying accompanies warming, since replacement of mosses by deciduous species will result in increased rates of carbon and nutrient cycling.
N2-fixation rates (primarily by cyanobacteria) are predicted to increase by a factor of 1.5-2 as a result of temperature, moisture, and CO2 changes. This will produce a 25-50% increase in nitrogen input to arctic ecosystems, thus affecting the abundant N-deficient ecosystems in Greenland.
Increased nutrient availability, combined with higher temperatures, may result in a shift towards an ecosystem composition and structure having higher annual nutrient requirements, litter quality and tissue turnover rates.
As the area of Greenland wetland soils is small relative to the area of global tundra soils, an enhanced release of CO2 and CH4 from increasing peat decomposition is believed to have a relatively modest impact on global climate. It is unclear whether enhanced net primary production will offset increased decomposition rates, and thus whether the Arctic will continue to serve as a carbon sink.
Mineralization and Decomposition and soil mineralization rates are expected to increase
nutrient availability due to higher fluxes of oxygen to the soil organic matter, higher soil temperatures and higher nitrogen fixation rates. This will improve conditions for plant growth and soil nutrient mineralization.
High Arctic ecosystems are presently more limited by temperature than by nutrient availability, while the opposite characterizes Low Arctic ecosystems. Low Arctic plants show a greater response to nutritional increases than High Arctic plants, whereas plant response to temperature elevation is greatest in the High Arctic, stimulating development, reproduction and seed germination.
Generally, arctic vegetation is nutrient limited and almost all the nitrogen and phosphorous in the soil-vegetation system is bound in plants and soil microorganisms. Nutrients released by increased decomposition and mineralization would not necessarily be available to plants, since they are rather efficiently immobilized by soil microorganisms. It is uncertain, whether shrubs having mycorrhiza may circumvent microbial nutrient immobilization.
In polar deserts, herb barrens, and heaths in Northern Greenland, plant productivity and long-term differentiation of vegetation types are strongly correlated with increases in precipitation. In such areas, less moisture may lead to greater mortality, decreased seed germination and seedling survival.
Food quality of plants If CO2-fixation increases without a matching increase in nutrient uptake, the quality of plant tissue as a food resource is likely to decrease, due to a greater C/N ratio. This may reduce the growth and abundance of invertebrates and retard decomposition rates in soil microorganisms, both involved in litter breakdown. It may also affect herbivory, as herbivores would have to increase consumption in order to compensate for poor food quality and avoid malnutrition.
220.127.116.11 Marine ecosystems
The influx of freshwater from melting ice and river runoff may cause a shift in the structure of biological communities in the upper ocean layers (e.g. coccolithophorids to diatoms).
Increased UV-B radiation may induce a change in species composition of both zoo- and phytoplankton towards dominance of poisonous species and species of low food value. This could cause major changes in food chains. An increased nitrogen demand may reduce productivity. Inhibition of photosynthesis occurs in some species, while bacteria may be stimulated because of an increase in substance availability
A rise in sea surface temperatures at high latitudes will result in a longer growing season and higher productivity. It may also result in the extinction of some species while others proliferate. In southern waters temperature may not rise and the return of the cod may fail.
Reduced supply of relatively warm Atlantic water to upwelling sites will cause decreased ice-edge primary production, a general nutrient loss, and a decrease in bioproductivity. A potential risk is that the polynyas of North Greenland may freeze resulting in drastic changes for marine life including sea mammals and birds overwintering here.
Reduced sea ice will improve access by ships to harbours all over Greenland, but will cause problems for polar bears and seals. The polar bear (Ursus maritimus) migrates all around Greenland, but resident populations occur primarily in NW- and NE-Greenland. The breeding areas have stable winter climates, permanent snow cover, ice-covered inlets, and drift ice with abundant ringed seals (Phoca hispida), which depend on sea ice for breeding, resting, and as diving platforms.
It is expected that the southern limit for resident polar bear populations moves northward, since a decrease or periodic disappearance of sea ice reduce the abundance of the ringed seal. During a prolonged ice free period, polar bears would have less time to build up fat reserves. This may result in declining body condition, thereby lowering survival rate through the ice free period, reduce reproductive rates and reduce cub survival.
More rain in late winter and early spring is another threat to both polar bears and ringed seals. The rain may cause the birth lairs of seals and the maternity dens of bears to collapse. The dens are situated so deep in the snow that the weight of the snow above may crush females and cubs. Collapse of seal birth lairs in the upper snow layers can cause increased exposure of pups to predation by polar bears and arctic foxes. Thaw and melt events in a milder winter may also damage the dens and birth lairs.
Other mammals which are more dependent on open water and less well adapted to the extreme arctic climate than the ringed seal may benefit from a prolonged ice free period as long as their food chains are intact. Such animals are the walrus (Odobenus rosmarus), harbour seal (Phoca vitulina), harp seal (Phoca groenlandica) and bearded seal (Erignathus barbatus). However, some of the seals may be forced to seek areas for breeding and shedding hairs further north. Fewer incidents of ice entrapments of whales are expected.
The danger of seal plagues and other diseases may increase. High temperatures combined with large densities of seals may be responsible for the seal plagues caused by viruses earlier this century.
5.2 Climate change in the Faroe Islands
The North Atlantic region, including South Greenland and the Faroe Islands, is expected to warm less or at a slower rate than elsewhere in the Northern hemisphere. All atmospheric circulation models seem to agree that the North Atlantic region, including the Faroe Islands, will experience the slowest rate of temperature increase. Adding the cooling effect of the reduced North Atlantic Current, it is unlikely that the annual mean air temperature increase will exceed 1-2°C within the next century. The rise in winter temperature may be twice the rise in summer temperature. The risk of frost in the high mountains may be reduced. An increase in yearly precipitation is expected to be less than 4%. Gale frequencies are expected to increase.
Sea surface temperature may drop due to reduced thermohaline circulation. The sea-level may rise at a similar rate of 5 cm per decade as predicted for the British Isles. Sea-level rise is not expected to be compensated for by land rise. Estimates of sea-level rise vary from two to five times the rate of 10-25 cm observed over the past century.
5.2.1 Ecological implications
Only minor changes in terrestrial ecosystems are expected. The isolation of the Faroe Islands in the Atlantic Ocean may have the consequence that climate-induced changes in plant and animal life will be unbalanced. Thus, the rate of possible species loss from terrestrial ecosystems may not be counterbalanced by a similar immigration rate, resulting in reduced species diversity.
The greatest changes are expected at sea, although the uncertainty is also the greatest here as long as it is unsettled what happens to the North Atlantic Current. Warmer deep water could result in a redistribution of pelagic and benthic communities.
Impacts on plankton are similar to those mentioned for Greenland. Fish species that settle in shallow waters in the early spring like flatfish, lumpfish, and species with pelagic drifting eggs and larvae have a high risk of UV-B induced damages.
Effects on marine mammals and seabirds are expected mainly to concern spatial shifts in areas of food production and primary productivity (changes in upwelling sights), nesting and rearing sites, and increases in diseases and oceanic biotoxin production (both from temperature increase and current changes).
The reappearance of the cod seems highly dependent on what happens to sea currents. 3-4 times as many storms as normal in recent years have contributed to the disappearance of the cod by blowing the fry towards waters too cold for their survival. A reduction in water arriving from the south will worsen the already occurring lack of the fry's favourite food.