May 2, 2007

Arctic Ice and Polar Bears

A new study looking at observed and projected rates of Arctic sea ice loss concludes that the Arctic oceans are losing ice faster than expected considering anthropogenic greenhouse effect changes alone (or, alternatively, our expectations are in error). But before anyone goes off and starts pointing to the imminent demise to polar bears… oops, too late…

Even though neither the write-up of the new study by author Julienne Stroeve and colleagues, nor the press release accompanying it (put out by the National Snow and Ice Data Center), mentioned polar bears, the press was quick to make a connection. To wit:

CNN: “Declining ice levels also poses a threat to Arctic wildlife including polar bears, walruses and ringed seals.”

The Independent: “Researchers have found that the sea ice, which is essential for polar bears to hunt seals, is melting far more quickly than the IPCC has predicted, largely because of accelerated warming caused by man-made emissions of greenhouse gases.”

Environmental New Service: “The loss of Arctic sea ice is most often tied to negative effects on wildlife like polar bears and increasing erosion of coastlines in Alaska and Siberia.”

And this excerpt from a May 1, 2007, editorial in the Salt Lake Tribune :

Polar plight: Bears are endangered, should be protected

It shouldn’t be too difficult. The decision whether or not to list a plant or an animal as endangered should be based on science, as indeed it is in the Endangered Species Act. Trouble is, the act itself appears endangered by politicians for whom science is an obstacle.

The act specifies the conditions under which the survival of an animal can be considered in jeopardy. Scientists decide whether those conditions exist for any threatened species

Take the polar bear, for example. Scientists know that the bears are in trouble, and they know it is because the sea ice on which they live is melting. Summer ice decreased 8.59 percent per decade between 1979 and 2006. At this rate, the Arctic Ocean sea ice will disappear by 2060, sooner if the rate escalates.

Since polar bears depend on sea ice to hunt, breed and travel, the loss of it seems an obvious threat to their survival. The Center for Biological Diversity makes this point in its 154-page petition for listing polar bears as endangered. The National Fish and Wildlife Service concurs.

But Alaska’s new governor and a majority of its legislators oppose the listing, and it’s easy to see why. They are concerned about the survival of the state’s royalties and taxes coming from the oil industry - 85 percent of the state’s general fund - and a proposal to build a gas pipeline to the lower 48 states. A polar bear recovery plan might hinder Alaska’s oil and gas development, so Alaska officials claim the petition to list the bear as endangered is nothing more than a ploy by conservationists. They say the bear is being used as a poster animal by climatologists trying to drum up concern about climate change caused by burning of fossil fuels, which is probably true, as far as it goes…

Apparently all of the newspapermen are more concerned with spreading hype than with reporting on what we actually know.

The just-released full version of the Intergovernmental Panel on Climate Change’s Fourth Assessment Report (AR4) includes this graphic (Figure 1) from the paleoclimate chapter (Chapter 6). It depicts the extent and magnitude (in a somewhat crude sense) of the temperatures since the end of the last ice age. The y-axis of the chart is latitude (north in upwards) and the x-axis is time before present (in thousands of years, going backwards to the left). The colored lines and rectangles indicate spatial and temporal extent of temperature anomalies, yellows and reds are periods that were warmer than the pre-industrial period (which itself was about 0.5ºC-0.8ºC cooler than present), and blue shading represents periods cooler than the pre-industrial. Notice that north of about 30N, that there were many places and periods lasting many thousands of years, that were likely as warm or warmer than present—including vast areas of the far north (Arctic), including Greenland, the Nordic Seas and North Eurasia.

Figure 1. Timing and intensity of temperature deviation from pre-industrial levels. (source: IPCC, AR4, Chapter 6, p. 462)

The North Eurasia data comes from a paper by UCLA’s Glen MacDonald published back in 2000. Here is how the abstract of that paper reads:

Radiocarbon-dated macrofossils are used to document Holocene treeline history across northern Russia (including Siberia). Boreal forest development in this region commenced by 10,000 yr B.P. Over most of Russia, forest advanced to or near the current arctic coastline between 9000 and 7000 yr B.P. and retreated to its present position by between 4000 and 3000 yr B.P. Forest establishment and retreat was roughly synchronous across most of northern Russia. Treeline advance on the Kola Peninsula, however, appears to have occurred later than in other regions. During the period of maximum forest extension, the mean July temperatures along the northern coastline of Russia may have been 2.5° to 7.0°C warmer than modern. The development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions, including heightened summer insolation, the demise of Eurasian ice sheets, reduced sea-ice cover, greater continentality with eustatically lower sea level, and extreme Arctic penetration of warm North Atlantic waters. The late Holocene retreat of Eurasian treeline coincides with declining summer insolation, cooling arctic waters, and neoglaciation.

To summarize, for somewhere around 5,000 years, the summer temperatures along the northern coastline of Russia may have been 2.5 to 7.0C warmer than present, and such a warming was associated with reduced sea ice, among other things.

If today’s level of Arctic warming is pushing sea ice to shrink rapidly, then it would seem reasonable to think that yesteryear’s warming did the same—and probably more so, given that the climate was warmer for much longer back then.

And what effect did this multi-millennial warming have on the polar bears? Well, one thing is for sure, their existence today proves that they didn’t go extinct!

The most likely explanation is that they modified their behavior to adapt to the changing conditions, probably by spending more time on land foraging, hunting, denning than they would during cooler, icier periods. There is evidence that these are precisely the kinds of adaptations that the bears are making to best cope with today’s warming climate. So instead of perishing, the polar bears will adapt as best they can, as they always have.

Environmental activist Laurie David described polar bears in her recent series of pre-concert global warming lectures given during her ‘Stop Global Warming College Tour’ as being “cute and fuzzy” and then played a childish video clip taken from Gore’s “Inconvenient Truth” depicting, through animation, a presumably tired-of-swimming polar bear struggling to pull himself out the water onto a small chuck of ice, which subsequently breaks apart beneath him. The scene then widens to show the poor bear in the middle of a vast iceless sea, with no land in sight, left to swim on or drown trying. As we watched, we couldn’t help but wonder whether Ms. David would have altered her sympathetic “cute and fuzzy” description had a cute, fuzzy polar bear been unleashed to share the stage with her. And she thought the drunken frat boys had given her something to cry about.


MacDonald, G.M., et al., 2000. Holocene treeline history and climate change across northern Eurasia. Quaternary Research, 53, 302-311.

Stroeve, J., et al., 2007. Arctic sea ice decline: Faster than forecast. Geophysical Research Letters, 34, L09501, doi:10.1029/2007GL029703.

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