Sunday, November 6, 2011

How did polar bears survive the Holocene ?

In the debate about whether or not past climates have been warmer than the present we have to distinguish between 'detection' of anthropogenic climate change and 'impacts' of climate change. That the Earth's climate 6000 years ago seemed to have been warmer than now bears no relevance for the 'detection problem' but I think it is quite important for possible impacts.

Has solar radiation any influence on the temperature of the room I am now in ? It sees obvious to every one  that it has. It is warmer when it is sunnier and cooler when it is cloudy. However, I could put forward the argument that the solar radiation has no influence because when I once set up the heating really high, it was warmer than at any other time I can think of. Surely this argument is illogical. If we want to argue whether or not solar radiation has an impact on room temperature we should compare alike with alike situations.This means situations in which the heating was set exactly at the same level.
This is, however, the type of argument that is sometimes used to refute the effect of greenhouse gases in the atmosphere because 'thousand years ago or six thousand years ago" it was warmer than today. Well, at those times, the 'external heating' was different than today and thus we cannot compare directly both situations. It has to be always underlined that the basic tool, although no the only one, to  detect and attribute climate  change is the comparison of climate model simulations, in which models are driven with and without anthropogenic external drivers like CO2.

This being said, the possibility that Earth's climate may have been warmer than today is relevant for the discussion about climate impacts. Continuing with the example of my room, I can indeed argue that the warmer temperatures caused by a stronger solar insolation may be perhaps not so much damaging for my canary bird because when I had the heating turned on it seemed to feel quite happy. And this seems to be what happened with polar bears during the Holocene period that started about 10 thousand years ago. Two papers published recently, Funder et al. and Jakobsson et al. (with supplementary material including an interview with the leading author) have reconstructed the extent of summer sea-ice in the Arctic over most of the Holocene period, and both come to the conclusion that in extended periods of the Mid-Holocene the Arctic ocean was ice-free in summer. This conclusion is interestingly based on the analysis of ancient wood. Drifting ice in the Arctic ocean transports wood from the American and Siberian shorelines to Greenland. The species to which the driftwood belongs is an indicator of its origin. The wood can be also dated by standard radiocarbon methods so that a picture of the evolving sea-ice cover through the Holocene can be reconstructed. The absence of driftwood is thus an indication of ice-free or near ice-free conditions. It turns out that over a period of 2 thousand years, the limit of sea-ice minimum was located about one thousand kilometers to the north of its present position.

Obviously polar bears survived the Holocene. To my knowledge -and I may be ere completely wrong here - there are no geological records of mass extinctions of Arctic species during the mid-Holocene. This does not say any thing important for or against the influence on climate of anthropogenic emissions of greenhouse gases, but it does say something about the resilience of ecosystems to climate change


ghost said...

two questions from a layman:

* how fast were the change in that times? Similar to today? Adaptation is easier if there is more time.

* what is the political conclusion? We have more time? If we go on with CO2 emissions at current rates, will the temperature stop at Holocene levels? What happens if it not stops there? Do we need than geo-engineering in the future by more sophisticated generations?

Georg Hoffmann said...

I think a reduction of a population of a species like polar bears with something like 30000 individuals (more or less) to near nothing (~100) over a time period of 2000-4000 years can hardly be detected in fossil records.

One could look at genetic variabilty in order to find out if the species passed through a type of bottleneck.

As far as I know there is no doubt that polar bears live exclusively of seals and for hunting in summer they need sea ice. So most probable explanation is a strong reduction of the species and survival in small areas with sufficient ice.

Anonymous said...

Maybe polar bears are able to eat something else.

It is obviously for some people sometimes easier to question the reality than to question climate alarmism hokus pokus.


thingsbreak said...

With respect, I'm having difficulty believing that it's actually this hard for you to understand why the Holocene altithermal isn't a good analog for modern unchecked emissions driven warming in terms of something like polar bear survival.

First: the rates of change of orbital vs. modern warming are at least an order of magnitude different.

Second: polar bear populations now are almost certainly well-below their pre-commercial harvest levels, many (at least 8 of 19 populations) polar bear populations are in decline, and anthropogenic warming is an additional stressor atop many others.

Is it really that hard to understand?

eduardo said...


also with respect, may be your arguments are true, but you have not supported them here.

'First: the rates of change of orbital vs. modern warming are at least an order of magnitude different.'

why is this relevant here? The argument so far has been that without summer ice polar bears cannot survive. Well, they did survive over 2000 years (if those papers are correct), with less ice cover than today. They had longer time to adapt, that is true, but the rate of warming has no relevance for the sake of the argument. The driving factor is the lack of ice and not the rate of ice disappearance. Or perhaps you can explain us how polar bears could adapt ?

'and anthropogenic warming is an additional stressor atop many others. '

that is the point what we are discussing. Could you please offer an argument or evidence to show why is this so ?

Anonymous said...

Climate people often told me how dumb I was and polar bears were one of these "fascinating" love themes.

We know much about bears, we know much about mammals and Wikipedia tells me a lot about polar bears:

"The polar bear is the most carnivorous member of the bear family and (what we know) .."

"Studies have also photographed polar bears scaling near-vertical cliffs, to eat birds' chicks and eggs".

"The polar bear is an enormously powerful predator. It can kill an adult walrus, although this is rarely attempted."

"Polar bears have also been observed to eat a wide variety of other wild foods, including muskox, reindeer, birds, eggs, rodents, shellfish, crabs, and other polar bears. They may also eat plants, including berries, roots, and kelp, however none of these are a significant part of their diet."

"Being both curious animals and scavengers, polar bears investigate and consume garbage where they come into contact with humans."

It's not THAT difficult to read Wikipedia!

(Ich bin oft beleidigt worden weil ich etwas nicht wusste oder einfach weil ich eine unbequeme Frage stellte. Mir würde es niemals einfallen jemanden wegen Unwissenheit ohne Grund zu beleidigen.

Ich stelle jedoch fest, dass einige Leute nicht so denken wie ich und dass diese Leute es nicht einmal schaffen Wikipedia zu lesen, bevor sie Unsinn schreiben.)


greg said...

generally, it is almost impossible to disentangle the different stressors that exist for many threatened species nowadays - only rarely is there a simple cause-and-effect relation. my feeling as a biologist and phd-student in ecology tells me that eutrophication, invasive species and habitat loss/fragmentation (together) are far more important factors in threatening species than those slight changes in average temperatures that we got.

Freddy Schenk said...

What would be the main cause(s) for invasive species and habitat loss? Changes in temperature and salinity? Or isn't it strongly dependent on the region?

But you're right that, currently, direct non-climatic human impacts might dominate changes in some ecosystems. We just submitted a paper on the evolution of the Baltic Sea ecosystem since 1850 where nutrient loads clearly dominate over climate. However, recent years also show an impact of atmospheric changes.

But the Baltic Sea is not the Arctic Sea. Already in Baltic Sea but even more in the Artic I would not speak of slight temperature changes. They are quite large - up to +3-4 K since around 1950 in some regions of the Artic zone. And the shrinking ice-extent is obvious.

I just read the log book of Nansen's Fram expedition discribing the dependency e.g. of polar bears from hunting on the ice. There are not too many animals on land to be eaten by polar bears.

Anonymous said...

Georg Hoffmann,

I recall reading an article this summer about a study examining polar bear DNA.

which is based on

From this, I get that things were not as simple as a cheetah type “bottleneck” occurring with the bears during prior sea ice habit loss in the Holocene. Their genome seems capable of being preserved within that of brown bears (Ursus arctos) which has considerable placidity itself. It seems Lombrog may have been right - but more lucky than good.

That is not to say that there will be “polar bears” in the wild with the Arctic Ocean ice free by the summer solstice. The “barren ground” brown bears above ~Arctic Circle are small and scattered, reflecting sparseness that the land habitat the far north provides. While polar bears are opportunist, feeding on what they come upon like the browns, they exploit the greater abundance of the sea, and particularly the pack fringe.


Georg Hoffmann said...


Thanks. Very interesting links.

But in the light of a possibly disappearing species in the future it is not a great relief to think that the species dissapeared but probably their DNA can still be found in another species transferred by natural interbreeding. To get again real polar bears from this process it needs probably a couple of generations of brown bears? Cynically speaking: humans can do better by taking the full polar bear DNA, preserving it and bringing it back to Nature once there will be again summer sea ice (in a couple of 1000 years). Until then we still have a zoo and Knut.

greg said...

@freddy: ok i admit my view is biased towards terrestrial systems where temperature average changes of one or to degree propably don't have the same effects as in aquatic systems. but as terrestrial arthropods are clearly dominating the overall stock of species on earth, i think this bias is justified ;)

Anonymous said...

Everybody thinking about these things might come to the conclusion that "direct non-climatic human impacts might dominate changes in some ecosystems". Except some climate alarmists.

And what about the thousands of other species where the climate-link is close to ZERO.

Polar bears survived in zoos in Germany during the hottest summers ever. They eat nearly everything, and it is imo not climate that will make them disappear, but its anthropogenic nevertheless.

And when I read about surveys where overpopulation is no problem for 99% of the people, but hunger, water and climate, I realize what all this climate hysteria has already damaged in european peoples brains. We can't even save our brothers, the apes, how could we ever dare to save the polar bears, and I don't think about german zoos.


Anonymous said...

Georg Hoffmann,

knut? The common, folk derived, German name for Ursus arctos (like Alaskan use Brownes when referring to the animals that we share the neighborhood with)?

Yes, it’s small comfort to find evidence that polar bears have been through this before, but better than nothing. It is an example of eduardo’s point on the resilience of biology, but, just as in most things, caution is wise in applying that resilience too broadly. It depends.

Press release:


General news article with some details absent in the above links:


Hank Roberts said...

> resilience of biology

Climate Change and Speciation of Mammals -- Anthony D. Barnosky

"... How fast can we have genetic mutations and how long can we maintain populations in isolation? These things play out over hundreds of thousands of years on the time scale. The kinds of environmental changes that humans have initiated have been playing out only over a hundred-year scale...."

Barnosky was interviewed at the American Institute of Biological Sciences’ symposium “Evolution and the Environment,” at the National Association of Biology Teachers convention in 2005.

Georg Hoffmann said...

Knut got global (?) glory for being a particularly sweet little bear

in the Berliner Zoo, first one of his kind born in this zoo after 30 years (suggesting it might be auite difficult to keep the species alive in our zoos). Tragically he died with only three years and probably before his first adult relationship with a female bear. At this point music from per gynts suite "morning" can be heard and we start crying. Sniff.

Anonymous said...

Wikipedia again about the mammoth:

"However, such climate changes were nothing new; numerous very similar warming episodes had occurred previously within the ice age of the last several million years without producing comparable megafaunal extinctions, so climate alone is unlikely to have played a decisive role."


Anonymous said...

why are some climate alarmist as funny to think, polar bears need seeice to survive?
if there is no sea ice in the arctic, no food for polar bears will be there, yep, but the food will be somewhere in the arctic region and there you will find the bears, maybe more than now in the fucking cold ice...

greg said...

the ice bear in this context is a pretty much overrated mascot which is instrumentalized to fuel emotions in favour of the climate alarmists cause. one should always remember that its not mammals nowadays neither have it been dinosaurs 100 million years ago dominating live on earth. instead unicellular live has been ruling this planet for ~ 3.5 billion years and will do so when we are long gone ... no matter what the global average temperature will be!
besides this fatalistic view of life on earth in general we should think about the consequences of building up (and maintaining!) such a high standing stock of human biomass during the last 100 - 150 years, that's where all the true problems come from!

Hank Roberts said...

Anteros said...

Interesting post. The Holocene is one good example, but a small version of what the last million years have been like in terms of change and adaptation. There is no evidence of much speciation or extinction - life as we know it generally coped with 6,7,8 degrees of change in temperature. Also, for coral-like creatures, sea level changes of 400 feet or more - on occasion at rates 25 times that of the present. The coral we know today is essentially 200 million years old. My feeling is we have no conception of the adaptability of 'life'.

And those who are most alarmed (hi thingsbreak!) forget that except for viruses and bacteria we are the most adaptable organisms on the planet. We'll thrive - that's what we do!

Steve Funk said...

This source says that polar bears probably evolved from grizzly bears over a 20,000 year period. This is fast, but not fast enough to allow adaptation if there is a major climate change over 2 centuries. A more likely way for the species to survive is through refugia. Climate change is never uniform, and some suitable habitat is likely to remain (or to have remained in the holocene) somewhere in the circumpolar range of the species.