North American Cordillera

The North American Cordillera forms the “backbone” of North America. It is originates in the US state of Alaska, running through western Canada and the western United States, and continuing into Mexico. Although commonly associated with the Rocky Mountains, the North American Cordillera in fact encompasses a number of essentially continuous mountain ranges across western North America.

Together with the Andes, glaciers in the North American Cordillera show perhaps the most rapid rates of disappearance anywhere. Glacier National Park in the U.S. for example has become notorious for the disappearance of the very glaciers that gave the park its name – the last of which will almost certainly disappear by 2030. When Glacier National Park in the U.S. was created in 1910, it had around 150 glaciers; today, less than 30 remain, and those have shrunk by about two-thirds. In Western Canada, inventories by the University of Northern British Columbia indicates that ice cover has decreased between 11-25%, with rates of decrease from 2000-2005 double those of 1985-2000.

Severe losses will continue at a steep rate over the next several decades just due to current rates of warming. Even the median IPCC projections see the disappearance of virtually all North American glaciers outside the Arctic Circle by 2100. Any emissions higher than this will eventually result in essentially complete loss of all glaciers in the North American Cordillera. With high emissions (a global mean temperature rise exceeding 4°C by 2100), any substantial seasonal snowpack also will become a rarity in North America outside the Arctic. With very low emissions, however, glacier losses will slow and eventually stabilize, with at least remnants remaining, and snowpack will gradually return.

Photographic comparisons illustrate the loss of Grinnell Glacier, Montana, US, between 1910-2016. As a result of rising temperatures, Grinnell Glacier retreated leaving Upper Grinnell Lake to form; Gem Glacier (in the saddle at the top of the photo) lost height; and Salamander Glacier (right side of the photo) became a distinct glacier after fragmenting from Grinnell Glacier. (Source: US Geological Survey).

Societal impacts of cryosphere change in the North American Cordillera

As climate change impacts the cryosphere, more snow will fall as rain. Combined with rapid shrinking of glaciers, this affects the ability of the North American Cordillera to serve as a “water tower” for western North America, reducing its capacity to store freshwater year-round. Rising temperatures therefore will diminish the supply of freshwater downstream, threatening the availability of drinking water and carrying economic harm for farming. This will particularly impact the southwestern US, where rising temperatures have already paired with snowpack loss, leading to ever more severe drought conditions.Cryosphere change also is increasing the risk and unpredictability of natural hazards in the North American Cordillera. Retreating glaciers lead to increased risk of hazards such as landslides and floods, and decreasing snowpack increases the risk of wildfires, as well as catastrophic events such as mudslides in the wake of such wildfires. This causes loss of life and costly damage to infrastructure.Additionally, decreases in snow cover negatively impact snow tourism in North America – an important factor in many local economies.

What we can save

With 2°C sustained warming, glaciers in the North American Cordillera will lose the vast majority of their volume by the end of this century, impacting our children and grandchildren (orange line, figure below). In the high-emissions scenario for which we are currently on track (< 4°C of warming), no glacial ice will remain in this region in 2300 (red line, figure below). This has serious implications for future generations.However, if global temperatures remain at or below 1.5°C, we can still preserve small but significant amounts of North America’s glaciers. Glaciers would begin to stabilize in the twenty-second century (blue line, figure below). Snowpack also is projected to recover as temperatures drop toward pre-industrial levels. This has important implications for freshwater availability, security and hazard reduction, and North American economies.To keep temperatures as close to 1.5° Celsius as possible means 50% emissions reductions by 2030. The need for our children and grandchildren is urgent. Let’s get to work.

Figure based on Marzeion et al. 2012.