Arctic animals on land include small plant-eaters like ground squirrels, hares, lemmings, and voles; large plant-eaters like moose, caribou/reindeer, and musk ox; and meat-eaters like weasels, wolverine, wolf, fox, bear, and birds of prey. Climate-related changes are likely to cause cascading impacts involving many species of plants and animals. Compared to ecosystems in warmer regions, arctic systems generally have fewer species filling similar roles. Thus when arctic species are displaced, there can be important implications for species that depend upon them. For example, mosses and lichens are particularly vulnerable to warming. Because these plants form the base of important food chains, providing primary winter food sources for reindeer/caribou and other species, their decline will have far-reaching impacts throughout the ecosystem. A decline in reindeer and caribou populations will affect species that hunt them (including wolves, wolverines, and people) as well as species that scavenge on them (such as arctic foxes and various birds). Because some local communities are particularly dependent on reindeer/caribou, their well-being will also be affected.
Ice crust formation resulting from freeze-thaw events affects most arctic land animals by encapsulating their food plants in ice, severely limiting forage availability and sometimes killing the plants. Lemmings, musk ox, and reindeer/caribou are all affected, and dramatic population crashes resulting from ice crusting due to freeze-thaw events have been reported and their frequency appears to have increased over recent decades. The projected winter temperature increase of over 6°C by late this century (average of the five ACIA model projections) could result in an increase in alternating periods of melting and freezing. Inuit of Nunavut, Canada report that caribou numbers decrease in years when there are many freeze-thaw cycles. Swedish Saami note that over the last decade, autumn snow lies on unfrozen ground rather than on frozen ground in summer grazing areas and this results in rotten and poor quality spring vegetation.
Warming leads to other cascading impacts on arctic land animals. In winter, lemmings and voles live and forage in the space between the frozen ground of the tundra and the snow, almost never appearing on the surface. The snow provides critical insulation. Mild weather and wet snow lead to the collapse of these under-snow spaces, destroying the burrows of voles and lemmings, while ice crust formation reduces the insulating properties of the snow pack vital to their survival. Well-established population cycles of lemmings and voles are no longer seen in some areas. Declines in populations of these animals can lead to declines in the populations of their predators, particularly those predators that specialize in preying on lemmings, such as snowy owls, skuas, weasels, and ermine. A decline in lemming populations would be very likely to result in an even stronger decline in populations of these specialist predators. More generalist predators, such as the arctic fox, switch to other prey species when lemming populations are low. Thus, a decline in lemmings can also indirectly result in a decline in populations of other prey species such as waders and other birds.
Caribou (North American forms of Rangifer tarandus) and reindeer (Eurasian forms of the same species) are of primary importance to people throughout the Arctic for food, shelter, fuel, tools, and other cultural items. Caribou and reindeer herds depend on the availability of abundant tundra vegetation and good foraging conditions, especially during the calving season. Climate-induced changes to arctic tundra are projected to cause vegetation zones to shift significantly northward, reducing the area of tundra and the traditional forage for these herds. Freeze-thaw cycles and freezing rain are also projected to increase. These changes will have significant implications for the ability of caribou and reindeer populations to find food and raise calves. Future climate change could thus mean a potential decline in caribou and reindeer populations, threatening human nutrition for many indigenous households and a whole way of life for some arctic communities.
The present reduced state of Peary caribou (a small, white sub-species found only in West Greenland and Canada's arctic islands) is serious enough that a number of communities have limited and even banned their subsistence harvests of the species. The number of Peary caribou on Canada's arctic islands dropped from 26 000 in 1961 to 1000 by 1997, causing the sub-species to be classified as endangered in 1991. The decline of Peary caribou appears to have been caused by autumn rains that iced the winter food supply and crusted the snow cover, limiting access to forage. Also, annual snowfall in the western Canadian Arctic increased during the 1990s and the three heaviest snowfall winters coincided with Peary caribou numbers on Bathurst Island dropping from 3000 to an estimated 75 between 1994 and 1997.
The Porcupine Caribou Herd
The Porcupine Caribou Herd is one of approximately 184 wild herds of caribou globally, the eighth largest herd in North America, and the largest migratory herd of mammals shared between the United States and Canada. The Porcupine Herd has been monitored periodically since the early 1970s. The population grew at about 4% per year from the initial censuses to a high of 178 000 animals in 1989. During the same period, the populations of all major herds increased throughout North America, suggesting that they were responding to continental-scale events, presumably climate-related. Since 1989, the herd has declined at 3.5% per year to a low of 123 000 animals in 2001. The Porcupine Caribou Herd appears to be more sensitive to the effects of climate change than other large herds.
The ecosystem defined by the range of the Porcupine Herd includes human communities, most of which depend on harvesting caribou for subsistence. Among these are the Gwich'in, Iñupiat, Inuvialuit, Han, and Northern Tuchone whose relationships with this herd have persisted over many millennia. Historically, caribou have served as a critical resource, allowing northern indigenous people to survive the hardships of the severe arctic and sub-arctic conditions. Times of caribou scarcity were often accompanied by great human hardship. Records and oral accounts suggest that periods of caribou scarcity in North America coincided with periods of climatic change.
Today, caribou remain an important component of the mixed subsistence-cash economy, while also enduring as a central feature of the mythology, spirituality, and cultural identity of Indigenous Peoples. The harvesting of the Porcupine Caribou Herd varies from year to year, depending on the distribution of animals, communities’ access to them, and community need. The total annual harvest from this herd typically ranges from approximately 3000 to 7000 caribou. Responsibility for management of the herd and protection of its critical habitat is shared in Canada between those who harvest the caribou (mostly Indigenous Peoples) and the government agencies with legal management authority.
The Gwich’in and the Porcupine Caribou Herd
The Gwich'in have been living in close relationship with the Porcupine Caribou Herd for thousands of years. Gwich'in communities are named for the rivers, lakes, and other aspects of the land with which they are associated. The Vuntut (lake) Gwich'in of Old Crow (population 300) in Canada's Yukon, are located in the center of the Porcupine Caribou Herd's range, providing opportunities to intercept caribou during both their autumn and spring migrations. Average harvest of caribou is as high as five animals per person per year. Sharing among households in the community and with neighboring communities is an important cultural tradition and is also believed to help ensure future hunting success.
Climate-related factors influence the health of the animals and the herd's seasonal and annual distribution and movement. Climate-related factors also affect hunters’ access to hunting grounds, for example, through changes in the timing of freeze-up and break-up of river ice and the depth of snow cover.
Every spring for many generations, the Porcupine Caribou Herd has crossed the frozen Porcupine River to its calving grounds in the Arctic National Wildlife Refuge in Alaska. In recent years, the herd has been delayed on its northern migration as deeper snows and increasing freeze-thaw cycles make their food less accessible, increase feeding and travel time, and generally reduce the health of the herd. At the same time, river ice is thawing earlier in the spring. Now when the herd reaches the river, the river is no longer frozen. Some cows have already calved on the south side and have to cross the rushing water with their newborn calves. Thousands of calves have been washed down the river and died, leaving their mothers to proceed without them to the calving grounds.
Freshwater ecosystems in the Arctic include rivers, lakes, ponds, and wetlands, their plant and animal inhabitants, and their surroundings. Animal life in these ecosystems includes fish such as salmon, brown and lake trout, Arctic char, cisco, whitefish, and grayling; mammals such as beavers, otters, mink, and muskrats; waterfowl like ducks and geese; and fish-eating birds such as loons, osprey, and bald eagles. Climate change will directly and indirectly affect these animals and related biodiversity. Many of the effects will result from climate-induced physical and chemical changes to freshwater habitats. Of particular importance are increasing water temperatures and precipitation, thawing of permafrost, reductions in duration and thickness of lake and river ice, changes in the timing and intensity of runoff, and increased flows of contaminants, nutrients, and sediments. Freshwater ecosystems are also important to marine systems because they act as intermediaries between land and ocean systems, transferring inputs received from the land to the marine environment. Some examples of important physical and chemical changes that will affect freshwater ecosystems include increasing water temperatures, thawing permafrost, ice cover changes on rivers and lakes, and increasing levels of contaminants.
Water Temperature Increases
Increases in water temperature are likely to make it impossible for some species to remain in parts of streams and lakes they formerly inhabited. Less than optimum thermal conditions, combined with other possible effects, such as competition from invasive species moving in from the south, may significantly shrink the ranges of some arctic freshwater species, such as the broad whitefish, Arctic char, and Arctic cisco.
As rising temperatures thaw frozen soils, drainage of water from lakes into groundwater can occur, eventually eliminating the aquatic habitat in the area. On the other hand, collapsing of the ground surface due to permafrost thawing can create depressions where new wetlands and ponds can form, adding to aquatic habitat in these locations. The balance of these changes is not known, but as freshwater habitats disappear, re-form, and are modified, major shifts in species and their use of aquatic habitats are likely.
Ice Cover Changes on Rivers and Lakes
Lake and river ecology are strongly affected by ice cover and the timing of the spring melt. Ecological impacts will result from changes in the timing of ice break-up, which strongly affects supplies of nutrients, sediments, and water that are essential to the health of delta and floodplain ecosystems. Changes in ice timing and types also affect water temperature and levels of dissolved oxygen (required by most living things in the system). Changes in species composition and diversity and food web structure are among the expected results of these climate-induced changes. Reduced ice cover will also dramatically increase the exposure and related damage of underwater life forms to ultraviolet radiation.
Later freeze-up and earlier break-up of river and lake ice have combined to reduce the ice season by one to three weeks, depending on location, over the past 100 years. This trend is strongest over the western parts of Eurasia and North America and is projected to continue over the next 100 years, causing a general reduction in ice cover on arctic rivers and lakes, with the greatest reductions projected in the northernmost lands. Freeze-up and break-up dates respond strongly to warming because as ice melts, it results in further warming of the surface, causing more melting, more warming, and so on. Longer ice-free periods are projected to increase evaporation, leading to lower water levels, though this may be countered by the increase in precipitation projected to result from the greater availability of ocean moisture (where sea ice has retreated). These changes will affect whether the northern peatlands will absorb or release the greenhouse gases carbon dioxide and methane. Low flow and flood patterns will change, as will levels of sediments carried by rivers to the Arctic Ocean.
Warming is very likely to accelerate rates of contaminant transfer to the Arctic and increased precipitation is very likely to increase the amount of persistent organic pollutants and mercury that are deposited in the region. As temperatures rise, snow and ice accumulated over years to decades will melt, and the contaminants stored within will be released in melt water. Permafrost thawing may similarly mobilize contaminants. This will increase episodes of high contaminant levels in rivers and ponds that may have toxic effects on aquatic plants and animals and also increase transfer of pollutants to marine areas. These impacts will be amplified by lower water levels as higher temperatures increase evaporation (possibly countered by increasing precipitation in some areas). Increasing contaminant levels in arctic lakes will accumulate in fish and other animals, becoming magnified as they are transferred up the food chain.
Southernmost species are projected to shift northward, competing with northern species for resources. The broad whitefish, Arctic char, and Arctic cisco are particularly vulnerable to displacement as they are wholly or mostly northern in their distribution. As water temperatures rise, spawning grounds for cold-water species will shift northward and are likely to be diminished. As southerly fish species move northward, they may introduce new parasites and diseases to which arctic fish are not adapted, increasing the risk of death for arctic species. The implications of these changes for both commercial and subsistence fishing in far northern areas are potentially devastating as the most vulnerable species are often the only fishable species present. In some southern mainland areas of the Arctic, new arrivals from the south may also bring new opportunities for fisheries, and increased productivity of some northern fish populations due to higher growth may allow for increased fishing of some species.
The Arctic char is the northernmost freshwater fish in the world and occurs throughout the Arctic. Some populations are locked in lakes where they feed on midge larvae and grow very slowly. Other populations migrate to the sea in summer where they feed on crustaceans and small fish, and char in these populations grow more quickly. Increasing water temperatures in freshwaters, estuaries, and marine near-shore areas are likely to increase growth of both types of char, especially in the mid-latitudes of their distribution, assuming that there is also a parallel general increase in food chain productivity. This is likely to increase fishing opportunities, but may be offset by the effects of competition from new fish species.
Research on Arctic char in Resolute Lake, Canada suggests that rising temperatures cause an increase in respiration, which increases the accumulation of heavy metals in the fish. In addition, other climate-related changes described on the previous page are expected to increase the levels of contaminants in lakes. Furthermore, reduced ice cover in lakes, increased mixing between water layers, and other warming-induced changes are projected to result in lakes retaining more of the contaminants that flow into them.
The Arctic grayling is a stream fish with about a 12-year lifespan. In some northern locations, it is the only species of fish that occupies local streams. In Toolik Lake (a small lake on Alaska’s tundra), 25 years of data have been collected on the grayling, tracking each individual fish in the stream. Results indicate that while young grayling do well in warmer water, adults fare poorly, actually losing weight in warm years. Projected climate warming is thus likely to cause the elimination of this population, with no opportunities for other species to naturally come into the lake.
Long-term studies project that a warmer future will severely stress lake trout, with related impacts on the food web. Impacts on lake trout will be most severe in smaller lakes in the southern part of the trout’s range in the Arctic; effects in larger, more northern lakes may be positive, at least in the short-term. Long-term studies in Toolik Lake, Alaska project that a warmer future is likely to result in the elimination of this lake trout population. Research suggests that a 3°C rise in July surface water temperature could cause first-year lake trout to need to consume eight times more food than is currently necessary just to maintain adequate body condition. This requirement greatly exceeds current food availability in the lake.
Furthermore, the projected future combination of higher temperatures, a longer openwater season, and increased phosphorus in the water (released into streams as permafrost thaws) is expected to increase production of small aquatic life forms that consume oxygen, thereby reducing oxygen concentrations in deeper water to a level below that needed by lake trout (and some other living things), thus reducing the bottomwater habitat. With surface water warming beyond the threshold required for these fish, the trout will be squeezed into a shrinking habitat between the inhospitable conditions near the surface and those at the lake bottom. The loss of the lake trout, the top predator in this system, is likely to have cascading impacts through the food web, with major impacts on both the structure and functioning of the ecosystem.
Aquatic Mammals and Waterfowl
The distributions of aquatic mammals and waterfowl are likely to expand northward as habitats change with warming. Seasonal migration is also likely to occur earlier in spring and later in autumn if temperatures are warm enough. Breeding ground suitability and access to food will be the primary drivers of changes in migration patterns. For example, wetlands are important breeding and feeding grounds for ducks and geese in spring. As permafrost thaws, more wetlands (formed when previously frozen ground collapses) are likely to appear, promoting the earlier northward migration of southerly wetland species or increasing the abundance and diversity of current high latitude species. However, a parallel earlier timing of the availability of local food must also occur for these outcomes to be realized. Mammal and bird species moving northward are likely to carry new diseases and parasites that pose new threats to arctic species. Another potential threat from the northward movement of southerly species is that they may out-compete northern species for habitat and resources. Northerly species may have diminished reproductive success as suitable habitat either shifts northward or declines in availability or access.