Amstrup grasps at straws to defend his polar-bears-are-doomed computer model

Polar bear activist Steven Amstrup made an astonishing statement in an interview earlier this week — he insisted that the current rate of warming in the Arctic is greater than anything polar bears have lived through before. He also said that optimistic comments on the future of polar bears made by geneticist Matt Cronin a few weeks ago were “incautious” and “misleading.”

Polar bear cubs in den wikipedia

Previously, I described how a new paper by Cronin and colleagues confirmed that genetic evidence indicates polar bears have been around long enough to have survived several past Interglacial periods that were warmer than today (and therefore, would have had virtually no summer ice). Cronin, not unreasonably, had some critical things to say about computer modeled predictions that polar bears could not survive in an Arctic without summer sea ice.

On Monday, the Anchorage Daily News gave Amstrup a forum to rebuke Cronin for his comments. A similar story was also carried by the Washington Post. [In the same ADN article, geneticist Charlotte Lindqvist, offered an outdated argument against future polar bear survival that I’ll deal with later]

Today, I’ll address Amstrup’s ridiculous assertion that the current rate of warming, attributed by him primarily to human activities rather than natural variation, is something polar bears have never experienced in their evolutionary history (a period of more than 400,000 years!).

Let’s start with the offending portion of the news item (published March 31, 2014):

“Fellow scientists agree that polar bears have survived past warming and glaciation periods, but sharply diverged on whether past warming trends can be compared to the present one.

Steven C. Amstrup, scientist emeritus with the U.S. Geological Survey who wrote the report recommending polar bears be federally listed as threatened, and a longtime colleague of Cronin, said Cronin’s arguments are “incautious” and “misleading.”

In an email, Amstrup, now a senior scientist at Polar Bears International, noted that the current warming period is happening much faster than past cycles of glacial and interglacial periods, and includes human effects.” [my bold]

To counter Amstrup’s contention that polar bears have never before experienced such a rapid warming as they’ve seen recentlyhere are a few points that were explored in more detail (with references) in my November post, “Eemian excuses: the warm was different then, polar bears were fine.

In the winter – at the warmest point of the Eemian – there was no ice south of Bering Strait and forests grew as far north as the eastern shoreline of the Southern Beaufort (Tuktoyaktuk) and the southern Arctic Islands.

In the summer – at the warmest point of the Eemian – the Arctic was essentially ice free (except for a band of thick, multi-year ice north of Ellesmere Island).

In other words, the Arctic was much warmer at the height of the Eemian Interglacial than it is now.

But Amstrup says it is not the ultimate amount of warming that is critical for polar bears but the rate that it warms.

The only reliable data I know of on rate of warming comes from Greenland ice core data that records Arctic warming during the transition from the last Ice Age (i.e., the beginning of the Holocene Interglacial, which began about 11,500 years ago). This warming was extremely rapid by any measure – about 5-100C of that warming took place within 30 years or less (Alley 2000).

As far as I know, this is the only good data we have on the rate of warming over any period of time, during any transition into an Interglacial period, that is short enough to compare to current global warming rates since 1950 that are blamed by some people on human emissions of carbon dioxide but that others point out is well within natural variation.

While there are many good reasons not to accept the IPCC as the final authority on climate matters (e.g., see journalist Donna Laframboise’s documented revelations), it is perhaps an authority acceptable to Dr. Amstrup. The latest IPCC draft report, released earlier this week, says the Arctic (area above 66ON) has warmed approximately 10C per decade in winter and spring since 19801, about twice the global average rate (IPCC WGII Ch 28 March 30 2014 approved: 4).

That’s 30C over 30 years — much less than the 5-100C warming over 30 years that took place at the beginning of the Holocene Interglacial less than 12,000 years ago, which we know that polar bears successfully survived.

In other words, we don’t even have to go back as far as the Eemian Interglacial to refute Amstrup’s statement that polar bears have never survived warming as rapid as current warming.

Keep in mind that the polar bear survival models concocted by Amstrup and colleagues predict near-extinction of the polar bear under Eemian-like conditions.

This means that Amstrup needs to discount the Eemian Interglacial evidence of polar bear resilience to fairly profound sea ice changes (and to early Holocene Interglacial rates of warming) because it’s concrete proof that his polar-bears-are-doomed computer models do not reflect the reality of polar bear responses to changing ice conditions.

In fact, observations over the last 10 years have shown that polar bears are adapting quite well to the moderate amount of warming that has taken place since 1980.

Footnotes
1. Regarding Arctic warming, the just-released NIPCC summary (Climate Change Reconsidered II: Biological Implications 2014:viii) says this:

Neither the rate nor the magnitude of the reported late twentieth century surface warming (1979-2000) lay outside the range of normal natural variability, nor were they in any way unusual compared to earlier episodes in Earth’s climatic history.” .

References
Alley, R.B. 2000. The Younger Dryas cold interval as viewed from central Greenland. Quaternary Science Reviews 19:213-226. http://www.sciencedirect.com/science/article/pii/S0277379199000621

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