In the Antarctic, the picture is more complex, but two major ice shelf collapses over the past decade may be a sign of what’s to come.
Other warming signs
- In the Arctic, ice thickness has declined by over 40 per cent, and an area larger than the Netherlands is disappearing every year. Scientists predict Arctic sea ice could melt entirely within 70 years.
- The Greenland ice sheet — the biggest ice mass in the Northern Hemisphere — is losing mass from glacier discharge, accelerated summer melting and runoff.
- Melting permafrost is causing trees and buildings to fall down in the far North. Almost a quarter of all land in the Northern Hemisphere has permafrost under it. As it melts, carbon dioxide and methane stored in the ground is released.
- The warming in parts of Antarctica has already contributed to a decline of some Adélie and emperor penguin populations.
The consequences of warming
The Arctic marine ecosystem is tied to the presence and dynamics of sea ice. The Arctic marine food chain begins with ice algae that clings to the underside of the ice pack all winter, and creates a dense mat under the ice in spring. Some Arctic species travel halfway around the world to exploit the food sources that flourish along the edge of the melting ice. Removing this dynamic would have profound consequences for all Arctic life. If the sea ice is drastically reduced or the timing changed, we can expect the loss of many species that are reliant upon this special habitat.
Arctic animals that depend on sea ice
Walruses, which travel long distances on floating sea ice, may be particularly vulnerable. In a warmer future, sea ice will likely melt rapidly in the spring, shrinking quickly over continental shelf areas and withdrawing to the deep ocean of the central Arctic. This could be devastating to walrus, as females use sea ice as a platform from which to feed their young and teach them to feed, primarily on shellfish from the bottom of shallow continental shelf areas.
Many species of seal are ice-dependent, including the spotted seal, which in the Bering Sea breeds exclusively at the ice edge in spring; the harp seal, which lives at the ice edge all year; the ringed seal, which give birth to and nurse their pups on sea ice; the ribbon seal; and the bearded seal.
Polar bears would be threatened by any decline in ringed seal populations, their main food source. Moreover, polar bears are dependent on sea ice for hunting and transportation. The polar bears in Hudson Bay and James Bay already fast during the four ice-free summer months they are forced to spend ashore, and pregnant females fast for eight months. The extension that has already been observed in this ice-free period has resulted in decreased birth rates, and will soon lead to starvation and ultimately the extinction of local polar bear populations.
Sea ice also plays an important role in the Antarctic ecosystem, particularly as habitat for sea ice algae, the primary food supply for larval krill over winter. Krill are vital to the Antarctic food chain. Penguins, fish, sea lions, seals and many other full-time Antarctic residents rely on the ice ecosystem. Minke whales travel from half the world away to feast on the krill every spring.
Shrinking ice threatens people and communities
“What I’ve seen over the years is that there is earlier break up of the ocean, and the ice is getting much more difficult to hunt on than it used to be.” — Pete Schaeffer, Kotzebue, Alaska
People both in and outside of the Arctic Circle are at risk from climate change, but it is the indigenous people of the far North who are bearing the early brunt of it. Climate change upsets the dynamics of marine and coastal ecosystems that native cultures depend on. Because native people rely on wild fish and animals for both cultural and physical sustenance, they are directly tied to local sea ice ecosystems. They also rely on frozen ice and tundra for travel and hunting.
In addition, sea ice buffers villages against storms, and land-fast ice helps protect coastlines from erosion. Often, native villages are located on riverbanks, coastal bluffs and barrier islands that provide access to marine resources. A combination of rising sea levels, decreasing ice, increased erosion and more violent storms will wipe out villages — displacing many Arctic natives and forcing them farther from traditional hunting grounds.