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Has this been peer reviewed? Actually the warmest part of the Holocene was not 5,000 years ago, but 8,000 years ago.

I tend to follow Hansen's research, which is in disagreement with this.


We are now by the way at the warmest part of the Holocene- .15 C above the 8000 years ago- according to Hansen. C02 levels as well have not been this high in 17 million years.

Hansen says that ice shelves begin to behave 'differently' at this level of warmth- which they are.

Peter Ellis

Has this been peer reviewed?
The phrase (and link) "Writing in the journal Science" may be a clue. :-)


Nice reading just after posting alarmist stuff of a 2011 minimum.
We have to give these Danish scientists some credit, though. By giving their study some good 'peer reviewed' critic.
I'm no geographer, nor a climatologue. But I have some knowledge on trees. When I read 'drift wood from Siberia is mainly larch and from North America is mainly spruce' I get suspicious.
The composition of forests and vegetation has been extremely complicated since the final stages of the Wurm/Weichselien glaciation period. This should be much deeper exploited before using origins as a clue.
The other concern is obviously one of timing. Natural climate shift since the last glaciation period is expressed in hundreds of years (except during Dansgaard-Oescher events, when sudden change in ocean currents have occurred). Under AGW, the forcing is expressed in decades.
But it's interesting, Neven, to discuss research that doesn't immediately fit in our thinking.


Temperatures over the period have not been more than 0.5C warmer or cooler than the mid-line . The warmest part of the Holocene (the “Holocene maximum”) was about 8000 years ago, and according to Hansen, today’s temperature is about, or slightly above, the Holocene maximum:

“… we conclude that, with the global surface warming of 0.7C between 1880 and 2000, global temperature in year 2000 had returned, at least, to approximately the Holocene maximum.”

Note, this is to the year 2000, and temperatures have increased ~0.15C in the last decade, so:

“Global temperature increased 0.5C in the past three decades to a level comparable to the prior Holocene maximum, or a few tenths of a degree higher.”

Per Hansen and Sato January 2011


I'm not so sure about the 50% less ice than there was at the end of the 2007 melting season. I have read some stuff on the Holocene Climate Optimum in relation to ice, but seem to remember papers showing less ice in parts of the Arctic Ocean in particular periods, but not for the Arctic as a whole.

Nevertheless, the question is interesting. Why, if there was less ice during the HCO, wasn't there a tipping point?

I don't know if there was so much less ice than now for the whole 3000-year period, but the Anthropocene has just started. It wouldn't surprise me if things are going a bit faster right now than they did back then.

Further, there are no guarantees that things will stabilize in the near future, like it did in the HCO, because the warming at that time was caused by increased insolation due to an axial tilt of the globe, whereas this time the warmth is very likely caused by greenhouse gases.

This means that this time the warming is more uniform across the globe and the heat from lower latitudes gets transported towards the Poles. During the HCO the warming occurred mainly at the northernmost latitudes.

If I'm not mistaken Maslowski bases his forecast of ice-free summers before 2019 precisely on the transport of extra heat towards the North Pole, through ocean currents mainly.

In other words: the tipping point - if it exists - is not just caused by albedo changes. I can imagine things stabilizing when there is constant inflow of energy (insolation) that peaks at a certain moment, but perhaps it's different when the heat just keeps on coming in (warm ocean currents).

This year might be extra interesting in this respect. Weather patterns, ie wind, have started to slow down extent decrease as of two weeks ago. But there's a large area of ice that looks very weak. If these weather patterns stay as they are and extent decrease starts picking up in the next 2-3 weeks, this is a sign that the ice is melting in situ. And that means we have passed the point when winds were the dominant factor in determining extent minimum.

I'd love to have a closer look at this paper, but unfortunately Science demands a fee.



That is, we are already a little above the Holocene maximum. This matters because Hansen’s and Sato’s look at climate history (paleoclimatology) in this new research finds that it is around this temperature level that the large polar ice sheets start to behave differently. During the Holocene, the Greenland and Antarctic ice sheets have been relatively stable, as reflected in the stability of the sea level. But once substantial melting starts, the loss of heat-reflecting white sea-ice, which is replaced by heat-absorbing dark ocean water, produces an “albedo flip”:

Hansen repeats his view, first published in 2007 but widely ignored, that a 5-metre sea-level rise is possible. In fact, recent research by Blancon et al published in Nature in 2009, examining the paleoclimate record, shows sea-level rises of 3 metres in 50 years due to the rapid melting of ice sheets 123,000 years ago in the Eemian, when the energy imbalance in the climate system was less than that to which we are now subjecting the planet.

Looking at recent research on mass loss in Greenland and Antarctica:

“These data records are too short to provide a reliable evaluation of the doubling time, but, such as they are, they yield a best fit doubling time for annual mass loss of 5-6 years for both Greenland and Antarctica, consistent with the approximate doubling of annual mass loss in the period 2003-2008. There is substantial variation among alternative analyses of the gravity field data, but all analyses have an increasing mass loss with time, providing at least a tentative indication that long-term ice loss mass will be non-linear… We conclude that available data for the ice sheet mass change are consistent with our expectation of a non-linear response, but the data record is too short and uncertain to allow quantitative assessment. The opportunity for assessment will rapidly improve in coming years if high-precision gravity measurements are continued.

Further evidence of our lack of “cushion” can be found by looking at the warm Eemian inter-glacial peak 125,000 years ago, when it is generally understood that:

“… temperatures in the Eemian … were less than 1C warmer than peak Holocene global temperature”

In fact, Hansen and Sato conclude that:

“… global temperature was only slightly higher in the Eemian and Holsteinian interglacial periods than in the Holocene, at most by about 1°C, but probably by only several tenths of a degree Celsius.

Yet at these times:

“… some paleodata suggest rates of sea-level rise perhaps as high as 1.6 ± 0.8 metres per century and sea level about 4-6 metres above present-day values.”

“Earth at peak Holocene temperature is poised such that additional warming instigates large amplifying high-latitude feedbacks. Mechanisms on the verge of being instigated include loss of Arctic sea ice, shrinkage of the Greenland ice sheet, loss of Antarctic ice shelves, and shrinkage of the Antarctic ice sheets. These are not runaway feedbacks, but together they strongly amplify the impacts in polar regions of a positive (warming) climate forcing … Augmentation of peak Holocene temperature by even 1C would be sufficient to trigger powerful amplifying polar feedbacks, leading to a planet at least as warm as in the Eemian and Holsteinian periods, making ice sheet disintegration and large sea level rise inevitable.”


In summation

Hansen says

“Earth today is poised to experience strong amplifying polar feedbacks in response to moderate additional warming.”

We are perhaps already a few tenths of a degree above the Holocene maximum, and the system seems to be in the early stages of rapid change. It is widely expected Arctic sea-ice will be totally lost in summer with a few years to a decade or so, perhaps at less than 1C or warming. Very few scientists think Greenland would be stable in an Arctic with little or no summer sea-ice, and opinion is split as to whether it is past its tipping point already.

It is hard to argue that anything above the Holocene maximum (of about 0.5 degrees above the pre-industrial temperature) can preserve a safe climate, and that we have already gone too far. The notion that 1.5C is a safe target is out the window, and even 1 degree looks like an unacceptably high risk.

Douglas Hoen

May I suggest that following the work of a single scientist will not give you a good idea of current scientific knowledge, as we all have biases. Also, the journal Science is a top-tier journal and usually publishes top-notch research (i.e., better than your run-of-the-mill peer review). I think a main point of the article is to question current accepted wisdom, a noble scientific goal. The point of science is to objectively consider all available evidence (and draw your own conclusions).

By the way, I have access to the paper, if you have somewhere I can send it...

Noel Ward

Something to think about is the terminology used and how stories like this get reported. The thing that's bound to come up and be misinterpreted is "tipping point." What does it really mean? It can certainly posit a massive change, but in the case of Arctic ice does it have to mean an ice-free Arctic?

I suggest that it does not. It can certainly be a point at which there is dramatically less ice all year round, with limited recovery during winter, but not necessarily an ice-free Arctic ocean. Maybe this is just semantics, or ice-free is meant infer a navigable ocean.

Still, the article is interesting and I'll get a copy of Science at my local library to read the whole thing. A pending tipping point or not, the global temperature is clearly going into uncharted territory, and with lots more people around than there were at the Holocene maximum. This is not the kind of risk that's good.


A big hooray for posting this article on your blog. it shows that you are open minded and do not shy away from posting pieces that do not agree with the opinion of most commenters.
As Douglas above comments, since this piece was published in a top-notch journal, it should not be dismissed just because it doesn't fit with our beliefs.
I do not have any scientific credentials allowing me to comment on these findings. My general feeling is that with sea ice as with everything else in nature, things are likely to be more complex than we first thought as we are finding out with the unexpected behaviour of sea ice this summer season. I wouldn't be surprised if Mother nature had some negative feedbacks in its bag giving us humans a chance. Hopefully we are able to see the light and grab this chance before it is too late!

Peter Ellis

In Arctic terms, "tipping point" is generally used to mean a point of irreversible change - i.e. the ice loss becomes self-sustaining such that the ice will not return even if conditions return to normal.

The Tietsche paper showed that weather-driven short-term perturbations do not lead to a "tipping point" : ice returns to the general level specified by climatology. This new paper suggests that even wholesale climate change does not lead to a "tipping point" : if the climate changes back, the ice returns.

I find both studies interesting but irrelevant. We have released the CO2 already, and are continuing to do so. The residence time in the atmosphere is centuries if not thousands of years. The climate isn't going to change back. As such, finding out that the ice will come back if the temperature drops is a bit like telling a homeless guy he could buy a house if he had some money.

What this study does do is put a minimum limit on the degree of ice loss we are already committed to. Holocene Optimum temperatures (lower than today's) led at equilibrium to loss of ~50% of Arctic ice. Since temperatures won't be coming down any time soon, that and more is what we're committed to for the next several centuries, at best, even if we stopped all fossil fuel use today.


Peter Ellis makes the point.

C02 at 392ppm is the highest in 15-20 million years. During the Holocene it was around 280ppm.

C02 is rising at the rate of 2ppm a year or more.

Dr. Hansen Hansen concludes that at the current temperature, no “cushion” is left to avoid dangerous climate change, and that the target goals “… of limiting human-made warming to 2° and CO2 to 450 ppm are prescriptions for disaster”.

The warming earlier in the Holocene stopped- and did not vary 0.5 degrees C plus or minus above a certain mean.

The warming in the pipeline now is substantial, and is not stopping.

Noel Ward

Peter's response confirms what I suspected. (thank you!) A tipping point is a point of irreversible change.

I have long agreed with Dr. Hansen. I do think we are approaching a tipping point in some respects. Temperatures seem unlikely to drop back, barring some other forcing such as a super volcano putting enough into the atmosphere to dial back temps for a while. But the CO2 will prevail.

Daniel Bailey

A copy of Funder et al 2011 can be obtained here.

R. Gates

A few thoughts about this study and about sea ice and tipping points in the climate. What there is no dispute about is that arctic sea ice has been at low levels in the past and that it has recovered. Hence, it is clear that sea ice on the arctic can recover from low levels. What is also known in some very broad terms are the causes (i.e. forcings) that led to periods of low sea ice during past periods and of course the key among these is the Milankovitch cycles. But, as others have pointed out, and is of course the central concern of our current climate period is that generally Milankovitch cycles and CO2 have cycled in tandem with each other, with Milankovitch initiating cycles of ocean warming that then releases more CO2 which causes more warming and so forth. Human activities have broken this relationship such that now anthropogenic CO2 can be seen as a forcing to the climate separate from the Milankovitch cycle. In this regard, it is perhaps irrelevant to look back simply to the Holocene optimum, as this study did, in which to compare our current period of higher CO2. We probably don't even want to look back just to the last interglacial period Of the Eemian around 130,000 years ago, but rather, we probably need to see what the sea ice might have been doing during the Pliocene period a few million years ago when CO2 was comparable to where it seems we're headed. If this is the case, it seem an much warmer and at least seasonally ice free arctic is in our future. See http://micropress.org/stratigraphy/papers/Stratigraphy_6_4_265-275.pdf

These kind of changes to the arctic alone will alter weather patterns in both hemispheres.

So what of "tipping points"? I think this is a term and subject that is widely misused and misunderstood, and can be the subject of many long blog posts. Suffice to say that if weather patterns and climate are altered-- isn't that already a tipping point that has been crossed? And though sea ice could recover to some extent, to the degree that any species goes extinct because of anthropogenic climate change-- what would a "recovery" of sea ice really mean to those species lost and that biosphere forever altered?


That is one rather interesting paper. Thanks for posting Daniel.

They do seem to be describing a rather well known trend...

At work now so just skim reading but do they explain the gap between 11 and 13 in the graph fig 1?


Reading more I find

"whereas the woodless
periods and the increase in spruce after 1400
show that situations with large BG* input became
increasingly frequent during the Little Ice
Age (LIA), as shown also in the western Arctic
Ocean (22)."

*(Beaufort Gyre)?

Kevin McKinney

". . .finding out that the ice will come back if the temperature drops is a bit like telling a homeless guy he could buy a house if he had some money."


Unless, of course, we are (rather against the odds) able to come up with a practical technology to draw down CO2 concentrations. But that, too, may turn out to be a lovely counterfactual dream.


I've not posted much here lately, because every time I visit I find that young Werther has already made whatever point I was going to. I saw "larch" and "spruce" and alarm bells started ringing for me, too. Great minds, and all that... ;^P

A read a paper (well, the abstract actually) which remarked on the changing vegetation in Siberia; the paper was about the changing albedo of differing vegetation cover (averaged across the year). It remarked that relatively high albedo deciduous larch is being replaced by lower albedo evergreen pine forests, such as spruce. Again the papers thrust was the feedback this change embodies.

But in the context of this new paper, where they say that the changes between larch and spruce reflect differing wind regimes, maybe they just reflect different vegetation regimes.

Its interesting, but I'm dubious about the interpretation.

k eotw

There's a load of momentum in the system.

It makes no sense comparing current ice levels today with ice levels 5000 years ago as if "we haven't got there yet" because current ice levels are probably not in equilibrium.

For all we know the momentum might be such that holding arctic temperatures at current levels for a decade or so would be enough to bring sea ice extent down to those past levels.

But you also have to take into account the momentum of human activity too. We aren't going to stop emitting CO2 tommorow so the arctic is very unlikely to have peaked in temperature.

As for tipping points try bringing back arctic sea ice once the ice sheets have collapsed.

Peter Ellis

I don't think anyone disputes that the land-based ice sheets have significant tipping points - i.e. if you magically removed them tomorrow, they wouldn't even start to grow back unless the temperature became substantially lower than currently.


Studies carried out in the 1950s and 60s on the remnants of the former Ellesmere ice shelf showed that it was formed 3000 to 5000 years ago. That was deduced from lines of driftwood inshore of the ice shelves which must have arrived there before the shelves formed.
Those studies support the idea of extensive sea ice at that time.
When the ice is greatly spread out - as it is now - trees being carried on the ice will tend to drop through. Check out the north pole cams for an example: a couple of surveyors poles have vanished, trees are a lot heavier.
Trees from Siberia are toppled into the rivers when floodwaters eat into the soil and topple the trees, roots and all. The number of trees flushed out depends on floodwater volume which is affected by contemporaneous melt rates of previous snowfalls.
The amount of timber reaching land is affected by the rate of the flooding that brought it to the coast and by the continuity or otherwise of the ice that carried it across the ocean. Sea levels are also a factor: a higher sea level means that less flood water is needed to increase water depth enough to carry a tree over the islands and bars of a delta.
If the authors of the current paper have not given sufficient weight to these factors then they may have made wrong conclusions about former sea ice extent.
As to tipping points: a tipping point isn't necessarily an all-or-none point. If the Arctic passes from a regime of ice extent having one range of values to a regime having a clearly different range of values, then it has passed a tipping point.
I have already remarked in my blog that the behavior and average extent range in the Arctic are far different than they were up to about 1950. We have already passed a tipping point. After the next tipping point, ice free summers will be the new norm.


Some of the points I raised above are covered in my blog. My 'Arctic Index' lists them.

'The Oldest Arctic Ice' is about the Ellesmere ice shelf.
'History Mysteries #2 - the sawdust coast' is about trees being flushed down to the coast of the Lena delta.
There is also a whole series on tipping points.

Kevin asked me what paper I was translating, but his comment is now buried in these many excellent comments.

Kevin: I have been transcribing and translating two papers by Ignaz Venetz. He was the first person to give scientific evidence of past climate changes which had caused changes in the extent of glaciation: i.e. ice ages. He published in 1821. Louis Agassiz, who is most often credited as the person who discovered the ice ages, did not begin to study the subject until 1836.
I have now published 5 articles on this, with a translation in hand, 50% complete.

Neven: by way of compensation for this shameless plug - I am trying to keep up with your welter of articles by linking them in my blogs. It is only rarely now that I can find time - and energy - to make much of a contribution here directly.

Rich and Mike Island

What I don't quite understand is how one accounts for old driftwood washing up on a beach 5,000 years ago, then remaining there 2,000 years, then floating or being carried by ice across the arctic ocean to another beach, and then getting washed to a new beach a thousand years after that. And so on.

Carbon 14 dating can help determine when the tree creating the driftwood died, but not the date it was transported. How would we know that there weren't some subsequent warmer periods with relatively low Arctic Ocean summer ice that permitted Arctic Ocean driftwood to be scrambled?


Re: dorlomin - their explanation for the lack of driftwood was that multiyear pack ice (which can carry driftwood) is replaced by year-round land fast ice (which impedes the driftwood) during these periods.

Having read the paper I don't think there is really anything that goes against what we know about arctic sea ice. Thanks to this paper we now have a much better history of it during the holocene, which is a good thing.

The paper clearly shows that warmer temperatures (through insolation or C02) will mean less ice, but that with cooling temperatures the ice will grow back, which I don't think anyone doubted.

Regarding tipping points. The first line of the paper states that "global warming will probably cause the disappearance of summer sea ice in the Arctic Ocean during this century". Obviously this will "tip" the arctic and arctic ecosystems into new and different regimes that will be profoundly negative for some species. But otherwise the paper itself doesn't discuss "tipping points" and my guess is that talk of a "runaway effect with disastrous consequences" is mostly journalist license from the BBC.


Thanks go out to Daniel 'The Yooper' Bailey for linking to the paper.

A big hooray for posting this article on your blog. it shows that you are open minded and do not shy away from posting pieces that do not agree with the opinion of most commenters.

If it's about the Arctic and from a reputable source, it belongs on this blog.

Neven: by way of compensation for this shameless plug - I am trying to keep up with your welter of articles by linking them in my blogs. It is only rarely now that I can find time - and energy - to make much of a contribution here directly.

Always a pleasure, Patrick! You are writing great stuff lately. I was thinking about your sawdust article when reading they used driftwood for this paper.


I think the journalist's POV is detectable in a couple of aspects of the BBC article.

I think the journalist shows a clear desire to combat any sense of urgency readers may have, by failing to mention that the "tipping point" issue has to do with the ability of the ice to recover *if temperatures decrease again, which they won't any time soon*, and by ending with these quotes:

"I don't say that our current worries are not justified, but I think that there are factors which will work to delay the action in relation to some of the models that have been in the media.

"I think the effect of temperature and global warming may cause a change in the general wind systems which maybe will delay the effects of the rapidly rising temperatures a little bit."

And by the way, what is meant by that last bit?


I just read the paper and agree that the tone of the BBC article does not capture the emphasis of the Science paper, which was that weather patterns changed during the Holocene in ways that are not captured in current models; just like it says in the Abstract. (By the way, the expression 'tipping point' is never mentioned in the article.)

The implication of the article is that changes in circulation and weather patterns during the Holocene Thermal Maximum (when the authors estimate that temperature in Northern Greenland were 2-4 deg C higher than today)acted to decrease arctic amplification in a way that allowed a sustantially diminished minimal sea ice cover to persist. If correct this is an interesting conclusion, (why this paper got into Science.)

This link at University of Washington shows some projections of maximal and minimal sea ice extents,kind of interesting to consider here; http://psc.apl.washington.edu/BEST/PSW2007/PSW07_modelpredictions.html


I listened to an interview with the Danish scientist, mentioned above, today on the Danish radio, and from what I learned, and I do understand Danish, his results is not like what I see discussed here or read in English reports, so I don't think he disagree with most of your guys!



My understanding of "Tipping Point" is, when the polar sea is not like we knew it nor for the polar bears who will suffer the most, the winter ice will always be there because of the lack of sun during that period.
The problem now and in the future, we have a lot of extend but no volume!!


Account Deleted

Hi everyone!

I saw an interesting graph on the dynamics of Grenladnskogo glacier.

Can we say that the dynamics of the Greenland ice and Arctic sea ice is the same?


Reading Paul Klemencic's recent post over on the SEI discussion thread about how a blockage of ice drift, "the buttress at Severnaya Zemlya", may give way leading to "The Big Arctic Flush", suggests another factor to consider in interpreting drift wood deposition. Funder et al. reference A. Häggblom, Geogr. Ann. A 64, 81 (1982). http://www.jstor.org/pss/520496 in describing drift wood movement through the Arctic Sea. If the ice moved more rapidly, the sea ice age requirement for driftwood transport could be altered.

Also, Häggblom indicates that conniferous wood can stay afloat for 10 to 17 months. How would driftwood transport be affected by seasonally ice free conditions?

Chris Reynolds

Jakobsson et al 2010 "New insights on Arctic Quaternary climate variability from palaeo-records and numerical modelling." PDF here: Their paper argues that during the Holocene Thermal Maximum (HTM) there was a sea-ice free state. However Jakobsson's finding of seasonaly ice free state is not comparable to the present as 65degN July insolation was some 40W/m^2 higher than present (see fig 1).

Insolation changes are however not comparable with changes in downwelling longwave due to CO2. The latter works year round including preconditioning of ice during the Winter. Furthermore CO2 increases cause cooling of the stratosphere, insolation changes don't, and changes in the AO propogate down from the mid stratosphere. Therefore changes in CO2 can reasonably be expected to have an impact on the AO and hence surface winds.

Recent findings regards the Arctic Dipole (which I'll blog on shortly) show a mode that is geared in both +ve and -ve modes towards warming the Arctic, not cooling it. And this mode has recently become more dominant.

So what I am saying is that findings regards previous periods in the Holocene do not seem to me to necesarily be instructive with regards current and future anthropogenically forced changes.

The inconsistency between modelled and observed (by proxy) sea ice could arguably be due to climatic variability in the models and between model runs and reality. However I've also been looking for papers describing an Arctic Dipole in projections/current state, and haven't found any (if anyone can suggest such I'd be grateful). Does this mean the models don't produce the AD, or does it mean that's not been explicitly studied?

Peter Ellis,
IMO the Tietsche paper tells us something useful about the mechanisms that respond to short term perturbations of sea ice extent. That it finds a virtuallly seasonally sea-ice free state only by 2050 isn't persuasive to me, I still think next decade at the earliest, highly likely by the 2030s. In my view once there's regularly less than 1M kmsq extent it's as near as damn-it (i.e. virtually) sea-ice free. Otherwise I agree, any talk about a tipping point must be made with respect to ongoing CO2 emissions. I still think we've just gone through the tipping point in that respect (the loss of multi-year ice).

Personally I disagree if you're saying current Arctic temperatures are equal to or greater than the HTM. Global Average is one thing, the Arctic is another. The fact that we don't see conditions to maintain a seasonally sea-ice free state now is telling us the HTM was warmer.

Did ocean currents drive the D-O events, or did wind changes drive both the D-O's and ocean currents. That's an interesting issue. FWIW I'm in the latter camp. As we continue to bias the environment against Arctic sea ice, bearing in mind it's pivotal role in NH circulation, the lesson that the atmosphere can radically shift circulation regime within a year or two should alarm us.

As we continue to bias the environment against Arctic sea ice, bearing in mind it's pivotal role in NH circulation, the lesson that the atmosphere can radically shift circulation regime within a year or two should alarm us.

Well put, Chris.

Kevin O'Neill

Many of us have read (and appreciated the wealth of knowledge contained therein) History of Sea Ice in the Arctic (http://bprc.osu.edu/geo/publications/polyak_etal_seaice_QSR_10.pdf). Svend Funder is one of the contributors.

I've had occasion to ask Dr Funder a few questions regarding several of his past papers, he's always taken the time to respond and answer my questions.

Driftwood is not a single line of evidence - Greenland's beach ridges are also proof that the Arctic Ocean was substantially ice-free 8.5 to 6 ka. Not surprisingly Dr Funder has also researched Greenland's beach ridges (Funder, S., Kjær, K., 2007. Ice free Arctic Ocean, an early Holocene analogue).

IIRC, Dr Funder at one time believed the Arctic must have been ice free in the early Holocene to create the beach ridges. When I asked him about this he replied, "We are presently working on a final synthesis of the results from northernmost Greenland. Here we argue that multiyear sea ice was reduced to between half and a third of the present during the Holocene Thermal Optimum." I believe the current paper is the one he was working on at the time.

Pete Dunkelberg

Funder et al. 2011 is a wonderful paper and a wonderful addition to this blog. It starts on a wonderfully empirical note:

Driftwood on Greenland’s raised beaches
and shores originates from transocean drift from Asia and America. The voyage takes several years....

and ends with this long paragraph (breaks and bolding inserted by me) arriving at specific significant room for improvement in climate models:

In general, our sea-ice record for North Greenland follows the Holocene climate development, with an early warm period followed by declining temperatures, which were punctuated by relatively warmer and colder intervals (17, 25).

The reduction of the HTM sea ice in
northern Greenland fits with the simulated ice
distribution and surface temperature in orbitally
LOVECLIM general circulation climate model
simulations (3, 4, 10).

A tentative first approximation
of the large-scale changes associated
with the observed ice retreat north of Greenland
can be obtained by selecting among the numerical
experiments performed with the LOVECLIM
model those that are the most similar to our observations
[experiments E3 to E5 (3) and fig. S3].

In this exercise, our records would correspond
in the model to an Arctic Ocean sea-ice cover
in summer at 8 ky B.P. that was less than half
of the record low 2007 level. The general
buildup of sea ice from ~6 ky B.P. agrees with
the LOVECLIM model, showing that summer
sea-ice cover, which reached its Holocene maximum
during the LIA, attained its present (~2000)
extent at ~ 4 ky B.P. (fig. S3).

However, despite
the similarities at large scale and the long-term
trends between model and observations, the complementarity
in sea-ice abundance between East
(Ellesmere) andWest (Greenland), which is seen
especially during the HTM, is not simulated in
the climate models. The largest reduction in the
EJM is indeed seen in the eastern part of the
Arctic in association with an enhanced oceanic
circulation and net northward heat transport (4).
However, there are no signs in the EJM or in
LOVECLIM of a concurrent simulated increase
in the West.

It has been seen in recent years that
there is a strong influence on the sea-ice variability
from the large-scale atmospheric flow anomalies
and associated wind stress (1, 2, 23, 24), and
the importance of wind-stress is also known from
basic sea-ice physics. Thus, it is likely that the
model deficits are related to a too-weak large-
scale AO-type flow response to the orbital forcing
during the HTM. Such troubles in reproducing
past sea-ice variations may also have an impact
on future simulated regional changes using the
same models. Therefore, improved understanding
of these inconsistencies is important.

[breaks and bolding inserted]

Along the way we gain interesting food for thought like

At ~2.5 ky B.P., an
era of dramatic centennial fluctuations in driftwood
abundance and of change of source areas

and also learn more about the famous MWP.

What a great experience for a team with many graduate students (I presume) to collect data along 500 km of wild, cold coast and then publish an important paper in Science! What a refreshing change of pace for this blog, excellent as it is, to look at a much longer perspective than "which way is the wind blowing at this moment."



It is interesting to read your comments, particularly your interactions with Dr, Funder. As I suggested earlier, one can see why this paper is in Science. It is useful and thought provoking. There are some important questions to be understood about how Arctic Sea Ice responds to warming.



the HTM 8,000 years ago- we are slightly above those tempertures now.

The amount of 'thermal or climatic inertia' for arctic temperatures at C02 at 280ppm at that time makes it highly unlikely that any melting in the arctic would approach that of the last 4 years.

As Hansen has said in his research paper- available at Columbia University.



Rich and Mike Island

I see we had a century break according to latest IJIS. One day doesn't mean much, but seems like the pause at the beginning of August is breaking. http://www.ijis.iarc.uaf.edu/seaice/extent/plot.csv

Chris Reynolds


You state:
"The amount of 'thermal or climatic inertia' for arctic temperatures at C02 at 280ppm at that time makes it highly unlikely that any melting in the arctic would approach that of the last 4 years."

But as I've shown above, July insolation, was around 40W/m^2 above current levels. July is a key period in the annual melt cycle. This ties in with Hansen's earlier arguments regarding early season melt period insolation in "Climate Change and Trace Gasses".

Hansen's new unpublished paper states:
"Consistent with our earlier study (Hansen et al., 2006), we conclude that, with the global surface warming of 0.7°C between 1880 and 2000 (Hansen et al., 2010), global temperature in year 2000 had returned, at least, to approximately the Holocene maximum."

That's global temperature, not Arctic and it's the Arctic temperature that is key to this discussion. I accept that we will, in due course, warm more than the HTM in the Arctic, but given the recent findings of lower ice extent during the HTM, the evidence points to present Arctic temperatures not being as high as during the HTM for the Arctic.

The warming durng the HTM was far less rapid than now. But it had longer to change the Arctic than we've had in the last century (with most of the global and Arctic warming in the last 35 years).

With regards inertia: Time alone may imply that as the ice had longer to respond during the holocene temperatures may not have been as high as now. However that angle neglects the additional regional warming due to open ocean and the sea-ice / ocean albedo effect, which is a large part of Arctic Amplification.

I've not read Hansen's paper fully, it seemed too similar to Climate Change & Trace Gasses, so it's not a priority for me. So if I've missed anything feel free to point it out. But if it reflects what you've repeated above I'm not convinced for the above reasons.

Kevin O'Neill,
Thanks for that information. With regards your quote from Dr Funder. Is it safe to assume he was referring to post 2007 conditions?

Rob Dekker

From the BBC article :

I don't say that our current worries are not justified, but I think that there are factors which will work to delay the action in relation to some of the models that have been in the media.

The models that have been in the media are the IPCC GCMs :

Considering that the IPCC GCMs project a 7 million km^2 September minimum for 2011, I'm not so impressed if any researcher claims that there are effects that 'delay the action' of some of these models.

I would be much more impressed by research that explains why on Earth the Arctic summer minimum is reducing so much more rapidly that anyone anticipated.


Thank you Chris for the clarification.

Yes, Hansen and Sato's recent research discuss global temperatures, and they are now at the highest of the Holocene era.

The warming in the earlier part of the Holocene, 8,000 years ago, had more time then the present As C02 has risen so rapidly in the past 50 years- and having only gone above 350ppm in the mid 1980s the time has been short for warming to took place compared to the much longer periods of the past in the Holocene.

That being so, with C02 so high, and despite 'climate inertia' in the system, the warming in the arctic will rapidly surpass the earlier event in the Holocene.


Well, the study makes strong claims and extrapolates 10,000 years of sea ice history out of 92 wooden samples. Of course there was once less ice than 2007 in the Arctic, the point is has it ever retreated that much within decades?


I would be much more impressed by research that explains why on Earth the Arctic summer minimum is reducing so much more rapidly that anyone anticipated.

= = = = = = = = =
What they found was a surprise — a layer of seawater about 200 metres below the surface that was actually colder than when it had been measured by previous expeditions.

“That's counterintuitive,” said Mr. Boxall. “We would expect to see, with global warming, warming conditions generally.”

But when they realized that the colder water was also saltier than they expected, an explanation began to suggest itself.

Mr. Boxall points out that the older sea ice is, the less salt it contains. Ice that's two or three years old already contains very little salt.

Year-old ice, however, remains fairly salty. And when it melts, it produces meltwater that's denser than the relatively fresh water from older ice.

As multi-year ice declines throughout the Arctic, more of the saltier meltwater from younger ice is mixing into the ocean. That colder, denser water sinks more quickly and forces less dense water from deeper in the ocean up to the surface.

Because fresh meltwater is colder than seawater, that means relatively warm water is being forced upwards. And that, said Mr. Boxall, may be part of the reason that sea ice is melting so much faster than anyone thought it would.


Inda House

Re: “Arctic 'tipping point' may not be reached”

The arctic warming during the Holocene Climate Optimum was caused by a huge solar forcing. That solar forcing has since receded allowing ice to accumulate again. But today’s melting of the arctic is not due to solar forcing, but a small anthropogenic CO2 forcing. However the change in albedo when the arctic melts will result in a forcing greater than our anthropogenic CO2 forcing. This is the point of no return - the tipping point which climatoligists are so worried about - because they know that once this point is reached, any reductions in CO2 emissions will not be able to overcome the albedo forcing.

Any suggestion that once arctic sea ice completely melts, that it can not return again, can definitely be viewed as a tipping point, but as indicated by Dr Svend Funder’s paper, a large change in forcing can let arctic ice build up again. Unfortunately we are not expecting such a large change in forcing to happen any time soon.


It was orbital and not solar forcing

Kevin O'Neill

Chris R. - Yes, my correspondence with Dr Funder took place in the last 18 months.



The paper does not just use driftwood to create their sea ice reconstruction. They have also mapped beach ridges along the coast. These are a record of open water at these sites and allow dating for times when their was seasonally open water/ year round ice/ icebergs etc.

Nor does the paper focus on how fast the ice retreated/reformed in the past, instead they provide a low resolution reconstruction of past arctic sea ice. This is a useful addition to our knowledge and will likely spur further research to improve our temporal resolution to help answer these sorts of questions. More generally we should take care not to, explicitly or implicitly, criticize the paper for not answering questions it never set out to answer.


Hi all,

I do think that the finding of 92 pieces of wood is a very shaky basis for reconstructing a past climate. Also, it was news to me that softwood does not float on water.

But these are just quibbles. These guys are scientists and I ain't.

I think that the most interesting aspect of the paper is that it suggests that there is a stable state for the ice, at 50% of 2007 minimum extent.

As the new graph from L Hamilton makes plain, it also seems that in the modern era, 2007 also represents a "step change" from what went before, with 2007-2011 showing much lower minima than 1979-2006.

Is it possible that there are several steps that we should anticipate going through on the way to a seasonally ice-free Arctic?

For instance, I might suggest that we may currently be in a semi-stable state where, as the marginal ice zones freeze later and later, more and more oceanic heat is released into the extreme cold of the polar winter atmosphere - taking heat away from the Arctic ocean, and serving to protect the remaining ice covered regions of the ocean.

We may see several years where this constitutes a balanced heat budget for the Arctic region - until increased warming leads to the the next "step change".

Daniel Bailey

@ idunno

Funder et al 2011 is an interesting study, but has little relevance to the circumstances we find ourselves in today.

In our world of today, CO2 is acting as a forcing to temps, not the other way around. If we were to cease all injected of GHG's into the carbon cycle and hold emissions at zero for 40 years, temps (and CO2 levels somewhat, due to various feedbacks) would continue to rise until equilibria was eventually reached.

Since the chances of mankind cutting emissions to zero immediately and holding them there is less than mine of ever playing centerfield for the NY Yankees, summer sea ice cover in the Arctic is effectively doomed. It is very likely that winter sea ice cover is kaput as well.

Thus, since temps in the Arctic will continue to rise for effectively generations and sea ice cover at some future date is already gone (depending on your understanding of time), the Funder study has no relevance to today.

Interesting, yes. Relevant, no.

Once gone, sea ice in the Arctic will stay gone for centuries-to-millennia.


Hi Daniel,

I'm not so sure. I think that, based on Lovelock, I expect massive negative feedbacks to kick in at some point.

In fact, I think they have already: when liquid seawater is in direct contact with the Arctic winter atmosphere, there is a temperature difference of anything up to 40 degrees C, which will inevitably lead to as massive heat transfer, and WACCY weather. But this also leads to a cooling of the Arctic Ocean.

Incidentally, I hope you will have spotted the recent scientific work on the subject which makes Neven upset, perhaps tying this to the major mass extinction of c.250M years ago.

Daniel Bailey

@ idunno

Unsure as to which recent work (250 MY ago ME) you refer to; can you give me a cite/link?

Wasn't getting into the "big" feedbacks, as they will be transitory compared to the ongoing CO2 forcing for which there exists no answer. FYI, I suspect Lovelock will prove correct in most of his conclusions, given our current course.

Lodger was kind enough to point me to this bit:

    Hansen and Sato, (2010) "Paleoclimate Implications for Human-Made Climate Change":

    "Hansen (2009) points out a negative feedback that comes into play as ice discharge approaches a level of the order of a meter per decade: cooling of the upper ocean by the ice. That negative feedback would be cold comfort. The high latitude cooling and low latitude warming would drive more powerful mid-latitude cyclonic storms, including more frequent cases of hurricane force winds. Such storms, in combination with rapidly rising sea level, would be disastrous for many of the great world cities and devastating for the world's economic wellbeing and cultural heritage."

    It's found on page 20, here:


I'm currently working on a blog piece that touches upon this and also on population response to climate change. To be published soon at SkS.


Hi Daniel,

As you may be aware, I'm particularly incompetent at linking to other sites. The terms "earth burp" typed into Google brings up several news stories, published around 22 July. The lead author is Micha Ruhl from Copenhagen - the gist that a relatively small amount of CO2 forcing, possibly volcanic, led to a massive discharge of CH4, with catastrophic results. Apparently we have been told "Don't panic", which is always a heck of a worry.

Thinking as I go along wrt these "step changes", I could change the terminology to say that the decline in sea ice could be characterised as "punctuated equilibrium". Looking at L Hamilton's bar chart on "Daily Graphs" here, there may even be 2 "step changes" visible already - one in 1998, a second in 2007.

Incidentally, I hope you will have spotted the recent scientific work on the subject which makes Neven upset, perhaps tying this to the major mass extinction of c.250M years ago.

I didn't read that.

I'm currently working on a blog piece that touches upon this and also on population response to climate change. To be published soon at SkS.

Let us know when you do, Daniel. This is one of the things that intrigues me more than the disappearing of summer ice per se.

Kevin McKinney

I, too, am awaiting that SkS post with ''[[;eager anticipation.'

Kevin McKinney

Sorry about the extra characters in that last comment--the cat got a pad onto the keyboard just as I hit 'post!'

Daniel Bailey

You're all too kind, but thanks!

Embargoed for now, but will be published in about 16 hours. The post is named "Where have all the people gone?"

(not like the Peter Graves movie)

Daniel Bailey

Now published, available here:

Kevin McKinney

Thanks, Dan--well-done, and quite sobering.


Here's Joe Romm's take on the Funder paper.


Hi all,

Some academics have been pinching my fine ideas about "step changes" -


no acknowledgement, no manners, no mention even of Professor Neven's fine blog...


And then there's this:


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