Late Friday afternoon the US Geological Survey (USGS) released a series of reports on the fate of polar bears in a warming world which Andrew Wetzler described in his post yesterday. The timing of the release may have been designed to minimize coverage but the reports themselves come through loud and clear: Arctic sea ice is shrinking due to global warming and as goes the sea ice so goes the polar bear. The New York Times picked up the story with the headline “Warming is Seen as Wiping Out Most Polar Bears.”

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.