We’ve seen the USGS predict that two-thirds of the polar bear population will be wiped out by 2050. But that analysis assumes the Arctic will still have summer ice then. The USGS acknowledges (PDF) their projection is “conservative” since it is based upon an average of existing climate models and “the observed trajectory of Arctic sea ice decline appears to be underestimated by currently available models.”

In fact, the Arctic now is poised to lose all its ice by 2030 — and possibly by 2020, as I discuss below. What will happen to the polar bears?

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“The survival of polar bears as a species is difficult to envisage under conditions of zero summer sea-ice cover,” concludes the 2004 Arctic Climate Impact Assessment (PDF) by leading scientists from the eight Arctic nations, including the United States. Another 2004 study by Canadian scientists agreed:

[G]iven the rapid pace of ecological change in the Arctic, the long generation time, and the highly specialised nature of polar bears, it is unlikely that polar bears will survive as a species if the sea ice disappears completely.

Why does the loss of sea ice threaten polar bears? The Canadian study “Polar Bears in a Warming Climate,” in Integrative and Comparative Biology, explains:

Spatial and temporal sea ice changes will lead to shifts in trophic interactions involving polar bears through reduced availability and abundance of their main prey: seals…. A cascade of impacts beginning with reduced sea ice will be manifested in reduced adipose stores leading to lowered reproductive rates because females will have less fat to invest in cubs during the winter fast. Non-pregnant bears may have to fast on land or offshore on the remaining multiyear ice through progressively longer periods of open water while they await freeze-up and a return to hunting seals. As sea ice thins, and becomes more fractured and labile, it is likely to move more in response to winds and currents so that polar bears will need to walk or swim more and thus use greater amounts of energy to maintain contact with the remaining preferred habitats.

Research by Claire Parkinson of NASA and Canadian scientist Ian Stirling “suggests that progressively earlier breakup of the Arctic sea ice, stimulated by climate warming, shortens the spring hunting season for female polar bears in Western Hudson Bay and is likely responsible for the continuing fall in the average weight of these bears.” The reality is quite grim:

“In 1980 the average weight of adult females in western Hudson Bay was 650 pounds. Their average weight in 2004 was just 507 pounds — a 143-pound reduction,” said Stirling. A 1992 study in the Canadian Journal of Zoology indicated that no females weighing less than 416 pounds gave birth the following spring.

When the ice goes, the polar bears will go. How soon could the ice go? New research suggests that the summer Arctic could be ice-free far sooner than anyone ever imagined.

Simply looking at the shrinking area of the Arctic ice misses an even more alarming decline in its thickness, and hence its volume. At a May 2006 seminar sponsored by the American Meteorological Society, Dr. Wieslaw Maslowski of the Oceanography Department at the Naval Postgraduate School reported that models suggest the Arctic lost one-third of its ice volume from 1997 to 2002. He made an alarming forecast (PDF):

If this trend persists for another 10 years — and it has through 2005 — we could be ice-free in the summer.

With stunning ice loss in 2007, this trend has not just continued, it has accelerated. The polar bear may be gone by 2020.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.