Gore's assertion that polar bears will become extinct due to global warming is an alarmist exaggeration

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An Inconvenient Truth claims that a study showed that polar bears had drowned due to disappearing arctic ice. It turned out that Mr Gore had misread the study: in fact four polar bears drowned and this was because of a particularly violent storm.

The thrust of the argument that echoes around the internet and appears over and over again in the popular press is the following sequence: 1. Anthropogenic CO2 causes the planet to heat. 2. This causes more summer ice melt. 3. The longer duration of open water in the summer and fall hampers the bear’s seal hunting and breeding. 4. Bear population diminishes.

Do a Google search on “polar bear,” “summer,” “ice” and “seals” and you will find an endless chorus singing this tune. A typical refrain of this song was recently sung in this Salt Lake Tribune editorial:

“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.”

There are three major arguments against the claim that disappearing ice, due to anthropogenic global warming, has severely impacted polar bear populations in recent decades:

1. All indications are that as temperatures have risen over the last several decades, polar bear populations have also risen.

2. It is quite clear the polar bears have survived periods of less Arctic ice than exists today.

3. Claims that current polar bear populations are being stressed by shrinking ice are greatly exaggerated.

Polar bear populations have risen as temperatures have risen.

It is clear that polar bear populations on the average have increased since the 1970s, about the same time temperatures started increasing in North America after several decades of no change or decline. There is strong agreement that the world population of polar bears is about 25,000 today. There is more controversy over what the population was in the 1970s. Reports range from 5,000 to 10,000.

There are some fringe arguments that the population in the 1970s was significantly higher than reported (and therefore subsequent reported increases smaller), but this flies in the face of the bulk of expert opinion and the experience of natives living and hunting in the effected regions. Those that argue the population was under counted in the 70s would be loath to say that the international hunting restrictions based on those low counts were therefore unnecessary.

But didn’t those same international hunting regulations negotiated and implemented in the 70s result in the increasing populations. Yes, they must be a contributing factor. To compare the impact of hunting to other causes of death, the other causes must also be quantified. But there is little accurate mortality information. The USGS’ Arctic Refuge Coastal Plain Terrestrial Wildlife Research Summaries states “Natural mortalities were not commonly observed among prime age animals, and we still know little about the proximate causes of natural deaths among polar bears.”

The world polar bear population is divided up into nineteen subpopulations. The IUCN World Conservation Union’s most recent polar bear population status reviews lists the “observed or predicted trend” for only five of these nineteen subpopulations as “declining.” These five subpopulations will be considered here one at a time:

Southern Beaufort Sea population. According to the IUCN’s analysis, early estimates (1986, 1988, and 1995) of this group put the population at about 1,800 bears. More recent data, collected between 2001 and 2006 put the number at 1,526. A definite decline, right? Not so fast, the IUCN puts the 95% confidence range for this number at 1,211 to 1841 bears. That is more than ± 20%. Oddly, no 95% confidence levels are mentioned for the earlier, higher estimates. But it is a pretty safe bet that those earlier estimates have an even higher uncertainty. Therefore, the old and new estimates are statistically not much different, which is acknowledged in the IUCN’s report.

Norwegian Bay population. Declines in this population can hardly be caused by reduced sea ice due to global warming (anthropogenic or otherwise). Why? Because, according to the IUCN “The preponderance of heavy multi-year ice through most of the central and western areas has resulted in low densities of ringed seals (Kingsley et al. 1985) and, consequently, low densities of polar bears.” (emphasis added)

Baffin Bay population. The IUCN says that the initial estimate (1984-1989) for this subpopulation was 300 to 600 bears. A second survey (1993 to 1997) estimated this declining population to be 2,074 bears. Please note that the previous two sentences are not the result of some bizarre typo. The extremely low initial numbers were presumably due to a flawed methodology (“…data collected in the spring in which the capture effort was restricted to shore-fast ice and the floe edge off northeast Baffin Island…” while “…recent work has shown that an unknown proportion of the subpopulation is typically offshore during the spring…”) How can the IUCN confidently conclude that this subpopulation is decreasing? Because the current (2004) estimate “based on simulations” is that the population is 1,600 bears. The reason for the decline is that the “subpopulation appears to be substantially over-harvested.” One of the reasons that it is over-harvested is that in 2004 Nunavut increased its hunting quota from 64 to 105 bears per year because “reports from Inuit hunters that polar bear numbers in BB had grown substantially.” Note that nowhere in this Orwellian story is the “decrease” in the Baffin Bay polar bear population blamed on receding summer ice due to global warming.

Kane Basin population. The only estimate of the Kane Basin population provided by the IUCN is 164, with a standard error of 35, and is undated. This represents about 0.65% of the world population of polar bears. The IUCN says that on the Greenland side of Kane Basin “the best estimate of the Greenland kill is 10 bears per year during 1999–2003.” The Canadian side has a hunting quota of 5 bears per year. If these numbers are at all accurate, with 10% of the bears being harvested each year, then this population is unsustainable and will clearly decline. However, no mention is made about decreasing summer ice being at all responsible for a decline. In fact, the IUCN says “the habitat appears suitable for polar bears on both the Greenland and Canadian sides of Kane Basin… and could be managed for subpopulation increase.”
Western Hudson population. There is a genuine decline in this population. According to the IUCN “Between 1987 and 2004” this population has gone “from 1,194 (95% CI = 1020, 1368) to 935 (95% CI = 794, 1076), a reduction of about 22%.” If the 95% confidence levels are ignored , this is a drop of about 10 bears per year over the 17 year period from 1987 to 2004. It is interesting to note that the government of Nunavut (which covers the northern portion of the western Hudson bear population) increased its hunting quota from 55 to 64 bears for the western Hudson subpopulation in 2004. At that rate, the number of bears harvested from this subpopulation every three years in the northern region alone is about equal to the entire 17 year decline for the entire region.

Polar bears have survived periods of less artic ice than exists today.

Polar bears have been around for a long time. According to the USGS “Polar bear genetics indicate that the species branched off from brown bears (Ursus arctos) and invaded an open niche on the surface of the sea ice during maximal extent of the continental ice sheets in the very late Pleistocene. Molecular genetic techniques suggest this could have occurred as long ago as 250,000 years.”

We live in the Holocene epoch, the time since the end of the last ice age. This relatively warm period, or interglacial, is about 11,000 years old. The Holocene epoch is one of two epochs contained in the Quaternary period, which is about 1.8 million years old. The other epoch in the Quaternary period is called Pleistocene. The thing that distinguishes the Quaternary period from the previous 65 million year old Tertiary period is that the Quaternary period is a “glacial age,” that is, on the average the planet has been colder than it previously was in the Tertiary period. The Quaternary Research Association describes the Quaternary as “…characterised by long periods (c.100,000 years) of cold climates interspersed with shorter periods (c.10-15,000 years) of warmer conditions.” Figure 1, below, shows a temperature proxy for the entire 1.8 million year Quaternary. Our current epoch, the Holocene, is one of those warmer periods, or interglacials.

Figure 1. 2.6 million years of climate as represented by and oxygen isotope temperature proxy. Peaks represent a warm earth, troughs a cold earth. The present is on the left side of the graph. The Quaternary is the last 1.8 million years. The narrow peaks in the Quaternary are the interglacials. Graph is from the Quaternary Research Association.

The previous 20, or so, interglacials in the Quaternary do not have the privilege of having their own epoch names simply because they did not occur during the era of modern civilization, and are therefore not as important to us today. But they were just as real as the Holocene. You can see these warm interglacials throughout the Quaternary in the oxygen isotope record, which serves as a temperature proxy, shown in figure 1 above. You can also see the last few interglacials from Gore’s “An Inconvenient Truth” temperature graph (also from proxy data) on pages 66 and 67 of his book, reproduced in figure 2, below. One thing jumps out: some of the previous interglacials were warmer than our current interglacial, the Holocene. This can clearly be seen to be the case for the interglacial previous to the one we are living in now (known as the Eemian interglacial).

Figure 2. Gore's "famous" temperature plot from pages 66 and 67 of "An Inconvenient Truth." I've blown up the plot and labeled the Holocene (the current interglacial) and the Eemian (the previous interglacial). Even Gore's data makes it plain that polar bears have survived much warmer periods than they are dealing with now.

Francis, et.al. (2006) used sediment cores at two lakes on Baffin Island, in the northern Canadian Arctic Archipelago to clearly show that the temperatures were considerably warmer during the previous interglacial (the Eemian), 120,000 years ago, than during the present interglacial (the Holocene). The authors conclude:

“During the last interglacial, summer water temperature estimates are warmer than at any time during the Holocene period at both sites. At Fog Lake, water temperature estimates for the interglacial are approximately 9 to 12 °C, compared with 5 °C at present. At Brother of Fog Lake, water temperature estimates for the last interglacial range as high as 16 °C, and throughout the peak of the interglacial average between 14 and 15 °C, whereas present temperatures are estimated to be only 6 °C … Our reconstructions illustrate that the previous interglacial in this region of the Canadian Arctic was warmer than at any time during the Holocene period.”

The 49 authors from 16 institutions in North America, Europe and Asia, collectively known as members of the North Greenland Ice Core Project (NGRIP), analyzed two ice cores from central Greenland. They reported in High-resolution record of Northern Hemisphere climate extending into the last interglacial period, in Nature in 2004 that “The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 °C warmer than today.”

But what about the Holocene itself? A plethora a data from multiple sources make it plain that in the arctic the early Holocene was warmer than it is today in the late Holocene, and that areas that are permanently covered with ice today were ice free earlier in this epoch.

The paper by Francis, et. al., mentioned above says, when referring to the Holocene, that all proxies indicate “…a warm period in the first half of the
Holocene followed by gradual cooling up to the present”

The following four papers confirm high temperatures in the arctic in the early Holocene:

1. A very interesting paper by Fisher, et. al. (2006) shows that the Bering Sea stock of bowhead whales and the Davis Strait stock of bowhead whales, which today are separated from each other by permanent sea ice were able to intermingle from about 10,700 years ago to about 8,900 years ago. Therefore the passage must have been ice-free at that time.

2. Koerner (1990) showed, based on the melt layers of High arctic ice cores, that in the Arctic “The warmest summers occurred 8-10 kyr ago and the coldest only 150 years ago.” So, not only was it the coldest early in the Holocene, but today’s warming seems to be a recovery from the coldest time in the Holocene.

3. In “Centennial-to-millennial-scale periodicities of Holocene climate and sediment injections off the western Barents shelf, 75°N”, Sarnthein, et. al., Boreas, Vol 32, 2003. Sediments “reveal a very early Holocene thermal optimum 10.7–7.7 kyr BP, with summer sea surface temperatures (SST) of 8°C.”

4. “Regional signatures of changing landscape and climate of northern central Siberia in the Holocene”, V.L. Koshkarova and A.D. Koshkarov, Russian Geology and Geophysics, Vol 45 No.6, 2004. In this paper “25 sections of Holocene deposits and soils of northern Central Siberia were studied” and demonstrated that “The main peaks of climatic changes of the postglacial history have been detected in the ranges 8.5-8.0 ka (thermal maximum) and 2.5-2.0 ka (thermal minimum),” where “the thermal maximum is characterized by warming up by 3- 9 °C in the winter, and by 2- 6 °C, in the summer.”

The mid-Holocene also appears to be warmer than the present as demonstrated in the following sources, which are graphically summarized in figure 3, below:

1. Solovieva and Jones(2002) studied a multi-proxy record of the Kola Peninsula in northern Russia concluded that for the period from 8000 years ago to 5400 years ago “A maximum of forest cover and the high Pinus abundance during this period indicate the Holocene climate optimum. The multiproxy data from Chuna Lake generally agree with the temperature reconstructions based on the evidence from the Greenland ice-cores (Stuiver et al., 1995) and summer temperatures were likely to have been 2°–3 °C higher than at present.”

2. Stewart and England (1983) examined more than 70 samples or Holocene driftwood on Ellesmere at 82° N Latitude. The time distribution of the driftwood indicates “prolonged climatic amelioration at the highest terrestrial latitudes of the northern hemisphere” from 4200 to 6000 years before the present.

3. MacDonald, et. al., (2000) dated Scots Pine wood (Pinus sylvestris L.) in Russia’s Kola Peninsula and found “the density of trees north of the modern tree-line was greatest between 7000 and 5000 BP.

4. Sarnthein, et. al.,(2003) studied sediments on the Barents shelf and found “disappearing sea ice from 6.4–5.2” thousand years before the present, and again “3.0–1.6 kyr BP.”

5. Matul, et. al., (2007) from the Russian Academy of Science studied microfossils from the Laptev Sea, which is north of Siberia and well within the Artic circle. They found that “Judging from the increased diversity and abundance of the benthic foraminifers, the appearance of moderately thermophilic diatom species, and the presence of forest tundra (instead of tundra) pollen, the Medieval warming exceeded the recent “industrial” one and is reflected in the near-delta sediments.” But they indicate that it was warmer even earlier by saying “..the warming in the Laptev Sea during the period of ~5100–6200 years B.P. corresponding to the Holocene climatic optimum could be even more significant as compared with the Medieval Warm Period.”

6. Koshkarova and Koshkarov (2004) draw their conclusions based on “25 sections of Holocene deposits and soils of northern Central Siberia [that] were studied by paleocarpological methods. Special attention was given to the reconstruction of the dynamics of speciation of forest cover in time and space.” These 25 sections are all above the arctic circle and range in longitude from 86 to 190°E. They conclude “The main peaks of climatic changes of the postglacial history have been detected in the ranges 8.5-8.0 ka (thermal maximum) and 2.5-2.0 ka (thermal minimum). Importantly, the thermal maximum is characterized by warming up by 3 - 9 °C in the winter, and by 2 - 6 °C, in the summer.”

7. Lawson, et. al., (2007) looked at glacial advances and retreats in Glacier Bay, Alaska. Glacier Bay is well south of the Arctic circle, but yields a rich history of northern latitude temperatures. They found a glacial retreat starting 6800 ago followed by a new glacial advance starting 5000 years ago. The retreat “was long enough to develop a mature forest.”

8. Francis, et. al., (2006) judged surface water temperatures on Baffin Island in the Canadian Arctic by analyzing midge remains in sediment cores. They report “a warm period in the first half of the Holocene followed by gradual cooling up to the present.”

9. In their study of Holocene temperatures in Iceland, Caseldine, et. al., (2006), analyzed chironomids and pollens from lake sediment cores and tree-line data. They show “that optimal summer warmth did not occur in Iceland until 8 kcal. yr BP at the earliest, possibly lasting until 6.7 kcal. yr BP. The amount of warming for July was therefore at least 1.5 °C, but possibly up to 2–3 °C higher than the 1961–1990 average.”

10. “Pollen, stomata, and macrofossils in a lake core with a basal date of 9700 14C BP were used to reconstruct past changes in climate and vegetation in the arctic tree line area, northeast European Russia” by Kultti, et. al. (2004a) They state in their abstact “We interpret summer temperatures to have been ca. 3–4 °C higher between ca. 8900 and 5500 BP than at present, and the lowest temperature regime of the Holocene to have occurred between 2700 and 2100 BP.”

11. In a very comprehensive study of the western Arctic Kaufman and coauthors from the US, UK, Canada, Norway, Iceland, and Russia (2004), studied proxies from over 140 sites in the western hemisphere part of the arctic. Their abstract notes “Paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer-than-present conditions at 120 of these sites. At the 16 terrestrial sites where quantitative estimates have been obtained, local HTM[Holocene Thermal Maximum] temperatures (primarily summer estimates) were on average 1.6 ± 0.8 ° C higher than present...” They found the timing for the thermal maximum to be a function of the longitude. The thermal maximum started earliest in the farthest west region, referred to as Beringia (Alaska and far eastern Siberia), perhaps as early as 11,000 years ago. Then, “HTM conditions in the Canadian Arctic Islands and the Greenland–Iceland regions, were reached 8.6±1.6 ka, with all but two sites reporting clear evidence of an HTM.” Once started, the thermal maximum lasted a long time: “On average, it lasted 2200±1300 yr in central and eastern Beringia, compared with 3100±1700 yr in northern continental Canada, and 3400±1400 in the Canadian Arctic Islands and Greenland–Iceland.”

12. In another paper, Kultti, et. al., (2004b) looked at tree lines in Finnish Lapland and found “Results indicate that pine reached its maximum distribution between 8300 and 4000 cal. yr BP. The inferred minimum shift in mean July temperature was at that time c. +2.5.”

Figure 3. It is commonly accepted among paleontologists that the Arctic was warmer in the early and mid-Holocene than at the presen. This graph shows a summary of the papers mentioned above as evidence for higher temperatures in the mid-Holocene. The left side of the graph shows the journal titles and authors. The right side shows a quote from the paper and period when the author provides evidence that it was warrmer than the present. These papers are representative of arctic areas over a wide range of longitutes in both the east and west hemispheres. Click on the image to see a larger version.

Stress on polar bear populations is greatly exagerated.

I have made a concerted effort to trace the stories about the drowning deaths of polar bears, as expressed in dozens of popular press articles and by many special interest groups, back to their roots. It appears that all such stories that can be traced at all go back to the same incident. This incident was reported by Monnett and Gleason (2006). Even they state “To our knowledge, we report here the first observations of polar bears floating dead offshore and presumed drowned while making apparent long-distance movements in open water.” (Emphasis added.) The circumstances of the drowning were extreme, as the authors explain: “Our observations suggest that polar bears swimming in open water near Kaktovik drowned during a period of high winds and correspondingly rough sea conditions between 10 and 13 September 2004” Somehow this single incident has been extrapolated to the impending extinction of polar bears due to anthropogenic global warming.

Caseldine, C., Langdona, P., and Holmes, N., Early Holocene climate variability and the timing and extent of the Holocene thermal maximum (HTM) in northern Iceland, Quaternary Science Reviews, Volume 25, Issues 17-18, September 2006. Get copy here

Fisher, D., et. al., Natural Variability of Arctic Sea Ice Over the Holocene, EOS Transactions American Geophysical Union, Vol 87, No 28, 2006. Get copy here

Francis, et.al. Interglacial and Holocene temperature reconstructions based on midge remains in sediments of two lakes from Baffin Island, Nunavut, Arctic Canada, Palaeogeography, Palaeoclimatology, Palaeoecology, 2006. Get copy here

Kaufman, D. S., et. al., Holocene thermal maximum in the western Arctic (0–180°W), Quaternary Science Reviews, Vol 23, 2004. Get copy here

Koshkarova, V.L., and Koshkarov, A.D., Regional Signatures of changing Landscape and Climate of Northern Central Siberia in the Holocene, Russian Geology and Geophysics, Vol. 45, № 6, 2004. Get copy here

Koerner, et. al., A record of Holocene summer climate from a Canadian high-Arctic ice core, Nature, Vol 343, 1990. Get copy here

Kultti, S., Oksanen, P., and Väliranta, M., Holocene tree line, permafrost, and climate dynamics in the Nenets Region, East European Arctic, Canadian Journal of Earth Science, Vol 41, 2004a. Get copy here

Kultti, S., et. al., Past changes in the Scots pine forest line and climate in Finnish Lapland: a study based on megafossils, lake sediments, and GIS-based vegetation and climate data,” The Holocene, Vol 16 No3, 2004b. Get copy here

Lawson, D.E.,et. al., 2007, Early to mid-Holocene glacier fluctuations in Glacier Bay, Alaska, in Piatt, J.F., and Gende, S.M., eds., Proceedings of the Fourth Glacier Bay Science Symposium, October 26–28, 2004: U.S. Geological Survey Scientific Investigations Report 2007-5047, p. 54-55. Get copy here

MacDonald, G., et. al., Radiocarbon dated Pinus sylvestris L. wood from beyond tree-line on the Kola Peninsula, Russia, The Holocene, Vol. 10, No.1, 2000. Get copy here

Matul, A. G., et. al., Recent and Late Holocene Environments on the Southeastern Shelf of the Laptev Sea As Inferred from Microfossil Data, Oceanology, Vol. 47, No. 1, 2007. Get copy here

Sarnthein, et. al., Centennial-to-millennial-scale periodicities of Holocene climate and sediment injections off the western Barents shelf, 75°N, Boreas, Vol. 32, 2003. Get copy here

Solovieva, N., and Jones, V., A multiproxy record of Holocene environmental
changes in the central Kola Peninsula, northwest Russia, Journal of Quaternary Science, 17(4), 2002. Get copy here

Stewart, T. and England, J., Holocene Sea-Ice Variations and Paleoenvironmental Change, Northernmost Ellesmere Island, NWT., Canada, Arctic and Alpine Research, Vol 15, No. 1, 1983. Get copy here

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A Semi-Empirical Approach to Projecting Future Sea-Level Rise," Rahmstorf, Science, Vol 315, 2007

Rahmstorf's sea level rise rate vs.T does not fit a line
Time for sea level to reach equilibrium is not millennia
Rahmstorf extrapolates out more than five times the measured temperature domain