Changes in climate are often cited as major threats to the future of Arctic caribou. Some change has already been observed, such as an increase in wildfires, earlier snowmelt and later onset of winter, changes in the formation of ice, and warmer temperatures. Future changes are not projected to be the same across the range of Arctic caribou in Canada, but all parts of the range are expected to see at least some further changes in the coming decades. The ways in which climate change is expected to affect caribou vary, and are listed below.
Changes to food
Some studies suggest that earlier springs might be good for caribou as it will give them access to higher quality food earlier, making them more healthy at a time when they are giving birth and feeding their calves. However, this advantage might ultimately be balanced by changes in the kinds of food available to them. As the tundra warms, there is evidence that the kinds of plants that grow there are changing. More woody plants are beginning to replace grasses and flowering plants, and the woody plants are less nutritious for caribou.
While food may be more available to caribou in the summer, it may become less available in the winter. Ice is a particular problem when it forms on, in, or beneath the snow. There is predicted to be an increase in freeze-thaw events where caribou live. This is when temperatures hover around the freezing point, and some snow melts, then it freezes again. This creates layers of ice in the snow pack, layers that caribou must dig through to get at the food beneath. These sort of events can lead to worse body condition for caribou, leading in turn to fewer calves being born. In extreme cases, icing has been blamed for starving caribou to death.
Predicted increases in forest fires will likely also become important for the migratory caribou that move to the treeline for the winter. It has been shown that caribou mostly tend to avoid burnt-out areas. This is likely due in large part to the damage that forest fires do to lichens, a primary winter food source for the caribou. Lichens can take decades to recover to the point that there are enough mature clumps to attract caribou.
Parasites and diseases
Warmer weather is anticipated to lead to caribou being more bothered by two types of flies that lay their eggs in the caribou, warble flies and nose botflies. When the caribou are bothered by these sorts of flies, they will often try to escape by running around, or by finding a more windy spot or a patch of snow where the conditions reduce the numbers of flies. Longer summers are expected to lead to more opportunities for the flies to lay their eggs in the caribou. The caribou can be affected by either losing opportunities to feed and wasting energy while they try to escape the flies, or by the effects of having the eggs of the flies hatch, and the parasitic larvae of the flies weakening the caribou.
Apart from existing parasites, there are concerns that warmer weather will lead to new parasites and diseases in the caribou range, possibly brought in by other animals such as moose and white tailed deer moving further north. A parasite called Besnoitia tarandi started to be noticed in eastern migratory caribou around 2005 and is cited in the COSEWIC report on the caribou as a possible limitation to productivity. In 2010, caribou lungworm, a parasite previously limited to the mainland was reported in caribou on Victoria Island. Climate change has been suggested as the likely cause of this northward movement of the lungworm. Chronic wasting disease, a disease that is hitting populations of wild deer in southern canada could potentially move north and infect caribou.
Changes to water and ice
The condition of ice is important to caribou as they use it for crossings during their migrations. caribou also cross open water when they must. The barren-ground caribou cross lakes and rivers. If the ice is not thick enough, or if water flows are too fast, caribou can drown. In one notable event in 1984, an estimated 10,000 caribou from the George River herd died after being swept over a waterfall in Nunavik (Northern Quebec).
The Dolphin and Union herd and Peary caribou cross sea ice. The Dolphin and Union herd is particularly vulnerable to changes in sea ice as it migrates across the ice twice a year, from Victoria Island to the mainland and back again. There have been several reports of caribou from this herd drowning, or freezing to death after falling through the ice or crossing open water.