Requiem for the polar bear

Well, for what it's worth, the U.S. Geological Survey has confirmed what just about every independent observer of the polar bear has been saying for years: time's running out. According to the executive summary of the service's initial findings as part of its investigation into whether to add Ursus maritimus to the Endangered Species list, the Alaskan population has as little as 45 years left until extirpation. The other North American populations could stick around a bit longer, but when the habitat is on the way out, things are pretty grim all over. To wit (emphasis mine):

Projected changes in future sea ice conditions, if realized, will result in loss of approximately 2/3 of the world's current polar bear population by the mid 21st century. Because the observed trajectory of Arctic sea ice decline appears to be underestimated by currently available models, this assessment of future polar bear status may be conservative.


12. Ultimately, we projected a 42% loss of optimal polar bear habitat during summer in the polar basin by mid century.

14. Using a simple deterministic model of future carrying capacity for polar bears, we forecasted that polar bears could be extirpated in the divergent ice ecoregion [north coast of Alaska and the Western Arctic coast in Canada] within 75 years, assuming that sea ice decline follows the mean trajectory predicted by the 10 models we used. If sea ice decline follows the minimum trajectory predicted, extirpation in this ecoregion could occur by year 45.

15. Using the carrying capacity model, we projected populations of polar bears in all other ecoregions to decline at all time steps, with severity of decline dependent upon whether minimum, maximum or mean ice projections were used. The only exception was a slight, temporary, increase in the polar basin convergent ice [Baffin Bay, I think] ecoregion for the 45 year timestep and the maximum ice scenario.

16. Based on a first-generation Bayesian Network model* incorporating a range of factors affecting polar bears, we forecasted extirpation of polar bear populations in the seasonal sea ice [Hudson Bay] and the polar basin divergent ecoregions by 45 years from present.

17. We forecasted extirpation of polar bear populations in the polar basin convergent ecoregion by 75 years from present. In the archipelagic ecoregion [Canadian islands], polar bears could occur through the end of the century, but in smaller numbers than now.

Of course, all of this is pretty much moot. Even if the polar bear is listed on the ESA list, all that means is the USF&WS would then be required to come up with a recovery plan. And since the cause of the problem is disappearing habitat due to climate change, it seems unlikely that even the service's best scientists will be able to find a politically viable solution to a problem that has flummoxed everyone else.

Note that the projections are based on a "business as usual" emissions scenario. In other cases that might be too pessimistic. After all, it is conceivable we will begin to reduce emissions at least somewhat in the next few decades. But unfortunately for the polar bear, the polar ice cap will almost certainly continue to melt regardless of what we do with our factories and automobiles, at least in the time frames involved.

Note also that while the 45-year extirpation prediction depends on a minimum ice coverage, the report concludes that their estimates may be conservative, because the current models do not take into account recent data showing record summer ice reduction. Predictions as to when we'll see an ice-free summer in the Arctic range from 13 to 40 years.


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