Polar bear-sea ice relationships: what biologists knew in ’72

1972 – a bit over 40 years ago. Seven years before we had reliable sea ice extent data from satellites and the year before the international agreement was signed by Arctic nations to protect polar bears from overhunting.

In 1972, a bear biologist by the name of Jack Lentfer was working for the Alaska Department of Fish and Game, stationed at the Naval Arctic Research Lab in Barrow. Lentfer was one of the founding delegates of the Polar Bear Specialist Group, where he represented US interests until 1981.

In the proceedings of the 1972 PBSG meeting (Lentfer 1972a), Lentfer stated the following in his report to the group:

“Long term warming and cooling trends occur in the Arctic and probably affect polar bear distribution and numbers. Climatic trends should be considered when assessing bear distributions and population data on a long term basis.” [my bold]

Warming and cooling, not just warming.

He also had a paper published that year (Lentfer 1972b), entitled “Polar bear: Sea ice relationships.” Forty years on, I thought it was worth having a look at what Lentfer told his fellow polar bear biologist colleagues back then.

Below is Lentfer’s introduction to his 1972 paper (there was no abstract):

Introduction to Lentfer 1972b

There is a discussion of different ice types, currents and ice movements, with the figure below included. This is of interest in giving us an idea of the minimum and maximum extent that was usual in 1972. It’s also interesting in that the map aspect is from the Pacific (US) perspective, with the Bering Sea at the bottom, while modern NSIDC maps have the Atlantic on the bottom. So I’m including it spun around, so it can be viewed as we are used to seeing sea ice maps today.

Figure 1. The top image appears to be the average sea ice extent maximum and minimum for the years around 1972, provided in Lentfer 1972. The bottom image is the same one, turned around to better compare with modern sea ice maps.

Figure 1. The top image appears to be the average sea ice extent maximum and minimum for the years around 1972, provided in Lentfer 1972. The bottom image is the same one, turned around to better compare with modern sea ice maps.

A bit further on, there is an interesting discussion about changing climate and changing sea ice cover.

Changes in ocean currents and climate affect sea ice. Vibe (1967)…distinguishes three different climatic periods, each about 50 years long, between 1810 and 1960, reflecting three stages of penetration of East Greenland ice into Davis Strait. He believes that conditions of 1810-1860 are now repeating themselves. He designates this as a drift ice stagnation stage where…Greenland ice does not penetrate far north into Davis Strait. The climate is cold, dry, and stable.

Several authors have presented data indicating that sections of the Arctic have experienced warming trends prior to about 1950 and have experienced cooling trends since that time. Zubov’s (1943) data show a warming of the Arctic for approximately 100 years prior to publication in 1943. He shows that Arctic glaciers have receded and the southern boundary of Siberian permafrost has moved northward. Zubov also present[sic] comparative data obtained during the drift of the “FRAM’ [1894] and the drift of the ‘SEDOV’[1937], 43 years later, over similar tracks in the Eurasian sector of the Arctic Ocean. The mean ice thickness was one-third less and the mean air temperature 40C higher in 1937-40 than in 1893-96. Dorf (1960) quotes Willett (1950) who states that in Spitsbergen mean winter temperatures have risen ~8[sic] between 1910 and 1950. …Mitchell (1965) states that world climate during the past century has been characterized by a warming trend from the 1880’s to the 1940’s. Thereafter, the warming trend appears to have given way to a cooling trend that has continued to at least 1960 with some evidence that it was continuing to 1965. [my bold]

As to the effect of this on polar bears, Lentfer had this to say:

A general warming of the Arctic could adversely affect denning. Change ice conditions because of a warming climate could result in fewer bears reaching some of the more favorable denning areas [on land]….Periods of cooling trends, during which the ice cover increased, should make more land areas, especially further south, accessible for denning.” [my bold]

From both of these examples, it is clear that back in 1972, Jack Lentfer realized that both warming and cooling trends should be expected in the future because both occurred in the past – and he made it a point to inform his polar bear biologist colleagues of the historical basis of that conclusion.

In 2012, Jack Lentfer (at the age of 80) was presented with a Lifetime Achievement Award by the Alaska Conservation Foundation.


Lentfer, J.W. 1972a. Alaska polar bear research and management, 1970-1971. Pg. 21-33, in Anonymous (eds.) Polar Bears: Proceedings of the 3rd Working Meeting of the Polar Bear Specialists Group, IUCN/SSC, 7-10 February 1972, Morges, Switzerland. IUCN Publications New Series, Supplementary paper No. 35. Gland, Switzerland and Cambridge UK, IUCN. http://pbsg.npolar.no/en/meetings/

Lentfer, J.W. 1972b. Polar Bear: Sea Ice Relationships. Bears: Their Biology and Management 2: 165-171.

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