A managed future could save polar bears from extinction

POLAR BEARS face a bleak future due to the polar ice loss caused by climate warming. Yet some hope remains if we can exert even limited control over greenhouse gas emissions, according to new research.

The iconic bears that so often feature in Christmas-time advertising and greeting cards were listed in 2008 as a threatened species.

This came after a study by the US Geological Survey that said a full two-thirds of the bears could disappear by 2050 if global warming was not brought under control. The polar bear (Ursus maritimus) is already under severe pressure due to habitat loss. The animals spend winter and summer on the sea ice watching near breathing holes for ringed and bearded seals as they come up for air. The problem is there is now less summer sea ice.

They eat very little while on land in the autumn as they wait for the sea ice to reform and can lose almost a kilo of body weight a day if deprived of their primary food source.

The research however was based on the “business as usual” model, a worst-case scenario for climate change. This assumes we will do little or nothing to control greenhouse gas emissions, something that would wipe out summertime Arctic sea ice by the middle of this century.

The new study, led by Dr Steven Amstrup, also of the survey, and colleagues from the University of Washington, carried out fresh calculations, but this time assuming that we manage to achieve at least some progress on greenhouse gas emissions.

The key issue was whether ice loss rose in step with rising air temperatures, or there was some hidden threshold, a “tipping point” temperature at which sea ice irreversibly collapses and disappears. “Such a tipping point would mean future greenhouse gas mitigation would confer no conservation benefits to polar bears,” they write this morning in the journal Nature.

In fact they found that there was no irreversible tipping point, just a direct relationship between rising temperatures and sea ice loss. They used a “general circulation model” that allowed them to test for different levels of mitigation. They found clear indications “that substantially more sea ice habitat would be retained if greenhouse gas rise is mitigated”.

They also showed that habitat retention “means that polar bears could persist throughout the century in greater numbers and more areas than in the business as usual case”.

The bottom line for the 22,000 polar bears estimated to exist in the wild is that their decline is “not unavoidable”, the authors say.

They describe the animals as “sentinels of the Arctic marine ecosystem”. So efforts at mitigation to help them “would have conservation benefits throughout and beyond the Arctic”, the authors believe.

Dr Amstrup does not underestimate the challenge however, particularly given our apparent inability to set meaningful mitigation targets.

The research showed that the bears would disappear from many areas. “But with mitigation and aggressive management of hunting and other direct bear-human interactions, the probability of extinction would now be lower than the probability that polar bear numbers will simply be reduced,” he said.