The threat to the polar bears is the kind of tangible consequence of global warming that could galvanize public opinion and help force federal action to curb emissions of heat-trapping pollution. Indeed the Fish and Wildlife Service was flooded with over 500,000 comments urging them to list polar bears as threatened under the Endangered Species Act. But if denial turns to despair without ever pausing at determination then the pressure to act will be diffused. This is where Mark Meyers, the head of USGS muddied the waters and the press went along for the ride. Meyers told reports that “Despite any mitigation of greenhouse gases, we’re going to see the same amount of energy in the system for 20, 30 or 40 years. We would not expect to see any significant change in polar conditions regardless of mitigation.”

Fortunately, Meyers’ assertion is not supported by the scientific reports released by the Survey. While it’s true that the climate system has a lot of inertia, meaning that some additional warming and sea ice retreat is inevitable, the likelihood of an ice-free Arctic—and polar bear extinction—depends heavily on how much more heat-trapping pollution is put in to the atmosphere. The climate models cited by USGS in fact show that if heat-trapping pollution concentrations could be stabilized at current levels (not a practical possibility) then no further loss of Arctic ice would be expected. USGS also examined model results for a range of emission scenarios developed by the Intergovernmental Panel on Climate Change (IPCC) and found that ice loss was indeed significantly less for the scenarios with lower emissions starting in about 2030. In a paper published last year, Marika Holland of the National Center for Atmospheric Research and colleagues found that periods of rapid decline in arctic sea ice are likely during this century if emissions are high, but that the risk of such abrupt ice loss is reduced for lower emission scenarios. 

Importantly, these findings are just based on the differences among “business-as-usual” scenarios developed by the IPCC. These scenarios were designed to explore alternative “non-intervention” cases, with variations in assumptions about economic and social developments, but without specific policies to limit global warming. The USGS report misconstrue this—asserting that the lowest of the IPCC non-intervention scenarios represents the best that can be hoped for with climate mitigation policies. But all of these scenarios would allow the concentration of carbon dioxide in the atmosphere to more than double compared with preindustrial levels.

The correct conclusion from the science is that all of the non-intervention scenarios threaten the survival of polar bears, but that lower emissions means lower risk. Polar bears still have a fighting chance if we take decisive action to cut global warming pollution in time to prevent carbon dioxide from reaching the levels considered by USGS.

The short story is that the Yellowstone population of Grizzly bears (which is isolated from Grizzlies in Glacier, Alaska, and Canada) depends heavily on White Bark Pine nuts to fatten up for winter. Unfortunately for the bears, White Bark Pines are being ravaged by unprecedented outbreaks of mountain pine beetles. While the beetles are endemic to Lodge Pole Pines, infestations in higher elevation White Bark Pines were rare until the last few years. Jesse Logan, a scientist who recently retired from the Forest Service, explained that the outbreaks in White Bark Pine are linked to warming temperatures, which allow the beetles to reproduce in one year, instead of two, at the elevation of 8-10 thousand feet where White Bark Pines are found. Diana Six, a scientist at the University of Montana, explained that drought also plays a role by weakening the trees' ability to defend themselves against beetle attacks.

I had read about this interaction last year when working on NRDC's report Losing Ground: Western National Parks Endangered by Climate Disruption, which includes it as an example, But reading about an ecosystem is nothing like seeing it. Friday afternoon we hiked up a steep slope in the National Forest Northeast of Yellowstone Park in search of beetles. At first glance the stand of White Bark Pines looked to be in good shape. While there were a few dead trees which had been killed by beetles in previous years, most of the White Barks appeared to be thriving. The area had never been logged (unlike Lodgepole Pine, White Bark Pine is not a commercial species) and we saw a number of trees that were more than 500 years old according to Jesse. The positive assessment didn't last too long. Louisa noticed a tree showing signs of an active beetle infestation. The tree was still green and I would have walked by it without noticing anything wrong, but Diana Six immediately pronounced it effectively dead. The telltale sign was tiny holes in the bark sprinkled with dry saw dust. With a few swipes of her hatchet Diana uncovered live beetles hollowing out the critical living tissue of the tree. From the air the next day we could easily see the red stains on the landscape indicating that entire stands of White Barks were being consumed by the beetles.

It's hard not to be depressed by this ecological tragedy, but I also saw some reasons for hope. In 1988, wildfires swept through Yellowstone, burning over one million acres. Today small White Bark Pines are regenerating the forest, finding toeholds next to boulders or fallen trees that provide a bit of protection from the desiccating heat of summer and killing cold of winter that prevails on the high alpine slopes where they find their niche. I can't help but think that these hardy organisms will find a way to survive if we just give them a chance by slowing the pace of global warming to improve the odds in their epic battle with the beetles.

Some pictures from the weekend: