Global warming due to climate change is a direct threat to biodiversity in all corners of the world. Its impacts are already visible and clearly affecting many ecosystems and human beings in many regions, although differently and at a different pace. Nowhere are its effects more visible than in the Arctic, hitting earlier and with greater intensity than anywhere else. The Arctic is warming at twice the rate of the global average, increasing the likelihood of severe impacts in the region. Effects on snow and ice were already felt in coastal circumpolar communities by the mid-2000s.

The overall impacts are very difficult to predict anywhere, and particularly in the Arctic because climate change will have both direct (for example warmer sea temperature, loss of sea ice) and indirect effects (increased human activities in areas not accessible until now) and will interplay with many other factors. The loss of Arctic sea ice is one of the most directly visible aspects of climate change.

Outline of the ice cap extent in 1979 (red line) and in 2016 © NASA

Marine mammals, as any other components of the Arctic ecosystem, will be strongly affected. The impact will vary according to the species’ specific ecology, from likely severe negative impacts on ice-dependent species (polar bears and ringed seals, for example) to likely positive impacts on seasonally migrating sub-arctic species (such as fin and minke whales). The geographical expansion of sub-arctic species to the Arctic, potentially beneficial to these species, will increase competition in the Arctic, modify food webs and potentially bring unknown pathogens.

Some consequences of climate change on marine mammals can already be seen from the decreasing blubber thickness of harp seals and minke whales in the Barents Sea and the changes in geographical distribution of minke and fin whales off Iceland and Greenland.

Environmental change is not restricted to global warming alone; the build-up of marine contaminants exacerbated by the build-up of microplastics are two of the many environmental changes that are currently taking place. Both can potentially severely affect Northern, and eventually worldwide, marine ecosystems as a whole, including marine mammals and humans (see more under Pollution).

Some observed and expected impacts of climate change

Melting ice flows off Kulusuk, East Greenland © Flickr / Mariusz Kluzniak

• Increasing ocean temperatures
• Reductions in sea ice
• Changes in ocean currents’ circulation, both globally and locally
• Rise in sea level
• Shifting and unpredictable weather effects

Other indirect impacts increasing potential effects

• Ocean acidification due to carbon pollution of the atmosphere (carbon dioxide reacts with sea water to produce carbonic acid, which increases the acidity of the water and changes the balance of minerals in the water)
• Building up of contaminants and micro-plastics (see more under Pollution)
• Increases in industrial development and human activities (see more under Disturbance)
• Increases in Arctic and trans-Arctic shipping with the possible introduction of invasive species and alien pathogens, and increased probability for disturbances, pollution and oil spills

Three examples of already observed effects affecting marine mammals

• Polar cod are declining in the Barents Sea, at least partly due to predation from Atlantic cod and competition with capelin, two sub-arctic species that are expanding their range
• Killer whales are appearing further north in areas where they were not present until now, increasing predation pressure on their prey, including belugas and narwhals
• The decrease in ice-cover quality and snow fall render the roof of the breeding lairs (burrow) of ringed seals less solid and protective, making it easier for polar bears and foxes to gain access to the pups, increasing pup mortality

You can read more on the consequences of the loss of Arctic sea ice for marine mammals here.