Polar Bears, Pt 2: “Habitat loss and inadequate regulatory mechanisms to address sea ice recession”


In support of its December 27 announcement of a proposed rule under the Endangered Species Act to list the Polar Bear as threatened throughout its range, the Fish and Wildlife Service issued a document for public review and comment. The document uses climate science findings on observed and projected Arctic sea ice loss and its relationship to global warming.  The bottom line finding: “We have determined that the polar bear is threatened by habitat loss and inadequate regulatory mechanisms to address sea ice recession.” The proposed rule has made it through the Administration’s process so far without being blocked, bringing the link between climate change impacts and endangered species into a high-profile regulatory proceeding. 

In its petition finding and proposed rule the U.S. Fish and Wildlife Service (FWS) (an agency of the U.S. Department of the Interior) announces “a 12-month finding on a petition to list the polar bear (Ursus maritimus) as threatened with critical habitat under the Endangered Species Act of 1973, as amended (Act). After review of all available scientific and commercial information, we find that listing the polar bear as a threatened species under the Act is warranted. Accordingly, we herein propose to list the polar bear as threatened throughout its range pursuant to the Act.”

In this document, scientists at the Fish and Wildlife Service have assessed climate and ecosystem science findings in a way that is relevant to policymaking and societal management. In contrast, the U.S. Climate Change Science Program, six years and more than $10 billion in spending after the National Assessment of Climate Change was completed, has yet to produce any assessment report linking climate change to its potential consequences or policy implications. 

The scientific heart of the analysis leading to the document’s main conclusion is on pages 30-73, in a section that addresses “Factor A”—“Present or Threatened Destruction, Modification, or Curtailment of the Species’  Habitat or Range.”

Pages 30-36 discuss:
—Overview of Arctic sea ice change
—Observed and projected changes in Arctic sea ice
—Projected changes in sea ice cover

This discussion is based on key findings and conclusions in international climate change assessments by the Intergovernmental Panel on Climate Change and the Arctic Climate Impact Assessment, as well as on observations, climate modeling, and process studies supported as part of the U.S. Climate Change Science Program, including work by scientists at NASA, the National Snow and Ice Data Center (affiliated with NOAA), and the National Center for Atmospheric Research and university-based scientists (supported by NSF).

Pages 36-68 then analyze the effects of sea ice habitat change on Polar Bears, including discussion of Polar Bear movement, distribution changes, effects on Polar Bear prey, reduced prey availability, demographic effects, open water habitat, reduced feeding opportunties, open water swimming, terrestrial habitat, access to and alteration of denning areas, and oil and gas exploration, development, and production.

Pages 68-73 state the Conclusion for Factor A.
Pages 128-133 state the overall Finding of the document.

Following is the text from pages 30-36, on Overview of Arctic sea ice change; Observed and projected changes in Arctic sea ice; and Projected changes in sea ice cover.  (Boldface emphasis added. We hope we haven’t introduced glitches in re-formatting from PDF to text.) 

A. Present or Threatened Destruction, Modification, or Curtailment of the Species’  Habitat or Range

Polar bears are believed to be completely dependent upon Arctic sea ice for survival (Moore and Huntington, in press; Laidre et al. in prep.). They need sea ice as a platform for hunting, for seasonal movements, for travel to terrestrial denning areas, for resting, and for mating. Some polar bears use terrestrial habitats seasonally, such as pregnant females for denning and some bears, all sex and age classes, for resting during open water periods. While open water may not be an essential habitat for polar bears because life functions such as feeding, reproduction or resting do not occur in open water, open water is a fundamental part of the marine system that supports seal species, the principal prey of polar bears, and seasonally returns to ice in the form needed by the bears. Further, the open water interface with sea ice is an important habitat in that it is used to a great extent by polar bears. The extent of open water is important because vast areas of open water may limit a bear’s ability to access sea ice or land. Snow cover is also an important component of polar bear habitat in that it provides insulation and cover for young polar bears and ringed seals in snow dens or lairs.

Overview of Arctic Sea Ice Change

Initial syntheses of climate models and environmental change data have identified potentially significant changes to the landscapes and biota in Arctic regions as a consequence of climate change (ACIA 2005, p. 1017; IPCC 2001a, p. 920). Climate trends are not occurring evenly or in a linear fashion throughout the world; Arctic regions are being disproportionately affected by higher levels of warming (Overpeck 2006, p. 1749). Observations of Arctic changes, including diminishing sea ice, shrinking glaciers, thawing permafrost, and Arctic greening, validate earlier findings (Morison et al. 2000, p. 360; Sturm et al. 2003, pp. 63-65; Comiso and Parkinson 2004, pp. 38-43; Parkinson in press).

Additional studies indicate that previous projections regarding the rate and extent of climate change underestimated the temperature trend, reductions to annual sea ice during the summer and winter periods, reductions to multi-year pack ice, and reductions in thickness (Rothrock et al. 2003, p. 3471; Stroeve et al. 2005, p. 2). Overpeck et al. (2005, p. 309) indicated that the Arctic is moving toward a new “super interglacial” state that falls outside of natural glacial-interglacial periods that have characterized the past 800,000 years. These changes appear to be driven largely by the albedo effect (see explanation in following paragraph), and there are few, if any, processes that are capable of altering this trajectory. There is no paleoclimatic evidence for a seasonally ice-free Arctic during the past 800,000 years (Overpeck et al. 2005, p. 309).

The National Snow and Ice Data Center (NSIDC is part of the University of Colorado Cooperative Institute for Research in Environmental Sciences, and is affiliated with the National Oceanic and Atmospheric Administration National Geophysical Data Center through a cooperative agreement) reported that the amount of sea ice in 2006 was the second lowest on record (since satellites began recording sea ice extent measurements via passive microwave imagery in 1978), and the pace of melting was accelerating. The latest sea ice measurements are thought to indicate that ice melt is accelerating due to a positive feedback loop. The albedo effect involves reduction of the extent of lighter-colored sea ice or snow, which reflects solar energy back into the atmosphere, and a corresponding increase in the extent of darker-colored water or land that absorbs more of the sun’s energy. This greater absorption of energy causes faster melting, which in turn causes more warming, and thus creates a self-reinforcing cycle that becomes amplified and accelerates with time. Lindsay and Zhang (2005, p. 4892) suggest that feedback mechanisms caused a tipping point in Arctic sea ice thinning in the late 1980s, sustaining a continual decline in sea ice cover that cannot easily be reversed. Results of a new study by a team of scientists from the National Center for Atmospheric Research and two universities, using projections from a state-of-the-art community climate system model, suggest that abrupt reductions in the extent of summer ice are likely to occur over the next few decades, and that near ice-free September conditions may be reached as early as 2040 (Holland et al., 2006).

Observed and Projected Changes in Arctic Sea Ice

Sea ice is the defining characteristic of the marine Arctic and has a strong seasonal cycle (ACIA 2005, p. 30). It is typically at its maximum extent in March and minimum extent in September (Parkinson et al. 1999, p. 20, 840). There is considerable inter-annual variability both in the maximum and minimum extent of sea ice. In addition, there are decadal and inter-decadal fluctuations to sea ice extent due to changes in atmospheric pressure patterns and their associated winds, continental discharge, and influx of Atlantic and Pacific waters (Gloersen 1995, p. 505; Mysak and Manak 1989, p. 402; Kwok 2000, p. 776; Parkinson 2000b, p. 10; Polyakov et al. 2003, p. 2080; Rigor et al. 2002, p. 2660; Zakharov 1994, p. 42).

Observations have shown a decline in late summer Arctic sea ice extent of 7.7 percent per decade and in the perennial sea ice area of up to 9.8 percent per decade since 1978 (Stroeve et al. 2005, p.1; Comiso 2006, p. 75). A lesser decline of 2.7 percent per decade has been observed in yearly averaged sea ice extents (Parkinson and Cavalieri 2002, p. 441). The rate of decrease appears to be accelerating, with record low minimum extents in the sea ice cover recorded during 2002 through 2005 (Stroeve et al. in press; Comiso 2006, p. 75). Average air temperatures across most of the Arctic Ocean from January to August 2006 were about 2 to 7 degrees Fahrenheit (F) warmer than the long-term average across the region during the preceding 50 years, indicating that ice melt is accelerating due to a positive feedback loop that enhances warming through the albedo effect.

Observations have likewise shown a thinning of the Arctic sea ice of 32 percent or more from the 1960s and 1970s to the 1990s in some local areas (Rothrock et al. 1999, p. 3471; Yu et al. 2004, p. 11). The length of the melt period affects sea ice cover and ice thickness (Hakkinen and Mellor 1990; Laxon et al. 2003, cited in Comiso 2005, p. 50). Earlier melt onset and lengthening of the melt season result in decreased total ice cover at summer’s end (Stroeve et al. 2005, p. 3). For 2002 through 2005, the NSIDC reported a trend of earlier onset of melt season in all four years; in 2005 the melt season arrived the earliest, occurring approximately 17 days before the mean melt onset date (NSIDC 2005, p. 6). The result of longer melt season is that the ice season is decreasing by as much as 8 days per year in the eastern Barents Sea, and by lesser amounts throughout much of the rest of the Arctic (Parkinson 2000a, p. 351). Comiso (2003, p. 3506) calculated an increase in the sea ice melt season of 10 to 17 days per decade. Subsequently, Comiso (2005, p. 50) included additional data from recent years and ice-free periods and determined that the length of the melt season is increasing at a rate of approximately 13.1 days per decade. Comiso (2005, p. 50) stated that the increasing melt periods were likely reasons for the current rapid decline of the perennial ice cover. Belchansky et al. (2004, p. 1) found that changes in January multiyear ice volume were significantly correlated with duration of the intervening melt season.

Projected changes in sea ice cover

A number of climate models have been developed that project future conditions in the Arctic, as well as globally (ACIA 2005, p. 99; IPCC 2001b, p. 471). All models predict continued Arctic warming and continued decreases in the Arctic sea ice cover in the 20 century (Johannessen 2004, p. 328) due to increasing global temperatures, although the level of increase varies between models. Comiso (2005, p. 43) found that for each 1 degree Centigrade (C) (1.6 degree F) increase in surface temperature (global average) there is a corresponding decrease in perennial sea ice cover of about 1.48 million km2 (.57 million mi2). Further, due to increased warming in the Arctic region, accepted models project almost no sea ice cover during summer in the Arctic Ocean by the end of the 21st century (Johannessen et al. 2004, p. 335). More recently, the NSIDC cautioned that the Arctic will be ice-free by 2060 if current warming trends continue (Serreze 2006, p. 2).

The winter maximum sea ice extent in 2005 and 2006 were both about 6 percent lower than average values, indicating significant decline in the winter sea ice cover. In both cases, the observed surface temperatures were also significantly warmer and the onset of freeze-up was later than normal. In both years, onset of melt also happened early (Comiso in press). A continued decline would mean an advance to the north of the 0 degree C (32 degrees F) isotherm temperature gradient, and a warmer ocean in the peripheral seas of the Arctic Ocean. This in turn may result in a further decline in winter ice cover.

Predicted Arctic atmospheric and oceanographic changes for time periods through the year 2080 include increased air temperatures, increased precipitation and run-off, and reduced sea ice extent and duration (ACIA 2005, tables on pp. 470 and 476).

Pages 128-133 present the conclusions, the formal “Finding” of the analysis.  Excerpts follow, with boldface emphasis added:


…In making this finding, we recognize that polar bears have evolved to occur throughout the ice-covered waters of the circumpolar Arctic, and are reliant on sea ice as a platform to hunt and feed on ice-seals, to seek mates and breed, to move to feeding sites and terrestrial maternity denning area, and for long-distance movements. Under Factor A (“Present or threatened destruction, modification, or curtailment of habitat or range”), we find that the diminishing extent of sea ice in the Arctic is extensively documented. Further recession of sea ice in the future in the future is predicted and would exacerbate the effects observed to date on polar bears. It is predicted that sea ice habitat will be subjected to increased temperatures, earlier melt periods, increased rain on snow events, and positive feed back systems. Productivity, abundance and availability of ice seals, a primary prey base, would then be diminished by changes in sea ice. Energetic requirements of polar bears would increase for movement and obtaining food. Access to traditional denning areas would be affected. In turn, these factors will cause declines in the condition of polar bears from nutritional stress and productivity. As already evidenced in the Western Hudson Bay and Southern Beaufort Sea populations, polar bears would experience reductions in survival and recruitment rates. The eventual effect would be that polar bear populations will continue to decline. Populations would be affected differently in the rate, timing, and magnitude of impact, but within the foreseeable future, the species is likely to become endangered throughout all or a significant portion of its range due to changes in habitat. This determination satisfies the definition of a threatened species under the Act.

Under Factor B (“Overutilization for commercial, recreational, scientific, or educational purposes”) we note that polar bears are harvested in Canada, Alaska, Greenland, and Russia, and we acknowledge that harvest is the consumptive use of greatest importance and potential effect to polar bear….We find that overharvest and increased bear-human interaction levels as a singular factor do not threaten polar bears throughout all or a significant portion of their range. Continued overharvest or increased mortality from bear-human encounters, however, may become more significant factors in the future for polar bear populations experiencing nutritional stress or declining population levels.

Under Factor C (“Disease and predation”) we acknowledge that disease pathogen titers are present in polar bears; no epizootic outbreaks have been detected; and intraspecific stress through cannibalism may be increasing, however population level effects are not believed to have resulted. We find that disease and predation as singular factors do not threaten polar bears throughout all or a significant portion of their range. Potential for disease outbreaks or increased mortality from cannibalism may become more significant factors in the future for polar bear populations experiencing nutritional stress or declining population levels. Both stressors warrant continued monitoring.

Under Factor D (“Inadequacy of existing regulatory mechanisms”) we find that the regulatory mechanisms in place at the national and international level are effective in addressing the short-term, site-specific threats to polar bears from direct take, disturbance by humans, and incidental or harassment take. These factors are, for the most part, adequately addressed through range state laws, statutes, and other regulatory mechanisms for polar bears. The ultimate threat to the species is loss of habitat, however, is not currently addressed at the national or international level [sic]. We conclude that inadequate regulatory mechanisms to address sea ice recession are a factor that threatens the species throughout all or a significant portion of its range.

Under Factor E (“Other natural or manmade factors affecting the polar bear’s continued existence”) we reviewed contaminant concentrations and find that in most populations contaminants are not determined to have population level effects….We find that contaminants, ecotourism, and shipping, while affecting or potentially affecting polar bears, as singular factors do not threaten the existence of the species throughout all or a significant portion of its range. However, the potential for future impacts from these sources may become more significant in the future for polar bear populations experiencing nutritional stress or declining population levels and warrant continued monitoring or additional studies.

Based on our evaluation of all scientific and commercial information available regarding the past, present, and future threats faced by the polar bear, we have determined that the polar bear is threatened by habitat loss and inadequate regulatory mechanisms to address sea ice recession. Other factors, particularly overutilization, disease, and contaminants, may become more significant threats to polar bear populations, especially those experiencing nutritional stress or declining population levels, within the foreseeable future.

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