Once the tipping points are crossed, the changes induced are so substantial and often abrupt that they fundamentally alter how an ecosystem functions. Scientists refer to these changes, irreversible on a century timescale, as ‘regime shifts’, from a shift to an ice-free summer, a collapse of Arctic fisheries or the transformation of tundra to forest.
Canada is at high exposure risk for 16 of the 19 such shifts, according to the Arctic Resilience Assessment report, more than any other Arctic nation, although Russia and the state of Alaska also suffer from significant exposure. All Arctic countries are vulnerable to at least 10 regime shifts.
As Arctic sea ice declines, there is less white ice to reflect solar radiation (albedo effect) that strikes it. The darker ocean surface then absorbs most of the radiation, and the warmer waters in turn lead to further sea-ice losses. These processes in turn affect how heat flows through the atmosphere, resulting in altered circulation patterns. As University of Victoria researchers have noted, altered circulation patterns also affect sea ice decline.
This ripple effect extends far beyond the Arctic. The global movement of water from the sea surface to the depths of the ocean (i.e. thermohaline circulation) can be disrupted by the release of large amounts of fresh water from melted polar ice that reduces the seawaters’ saltiness, thus lessening the density differences between north and south Atlantic waters. These gradients help drive water from the tropics to the north Atlantic, which in turn moves large amounts of heat around the world.
A collapse of these circulation patterns would substantially alter the world’s climate, in particular a southward shift of tropical rainfall belts, which would likely precipitate declines in farming productivity. The researchers say that a collapse of thermohaline circulation is unlikely, but the report also notes that some scientists believe that models are underestimating this risk.
Other regime shifts already underway include permafrost melt, a transition from tundra to boreal forest or grassland, coniferous to deciduous forests, peatlands from bogs to ecosystems more supportive of shrubs and trees, shifts of flora and fauna on the seabed from algae and filter feeders to seaweed, and a northward drift of temperate marine species. All of these transitions involve the conversion of one type of ecosystem to another.
The report also recounts how an ice-free summer opens up shipping routes and provides new access and economic opportunities for extractive industries—but it also reduces mobility across ice by people and animals, compromising traditional livelihoods, as well as ecosystems.
The report’s release comes amid unheard-of 20C degrees higher than normal air temperatures in the Arctic for this time of year.
Hydroelectricity has long been assumed to be a cornerstone of any future low-carbon economy, but disappearing glaciers are altering the equation