Inconvenient: New paper finds the last interglacial was warmer than today – not simulated by climate models

‘This implies that climate models are unable to fully simulate natural global warming,’ although to be fair their always able to simulate some global warming even if none has happend in reality .

This is nothing new. It has been well known for decades that the Eemian interglacial period was globally, 3 C warmer that our present day Holocene, and that sea levels were much higher. I am very disappointed in this new generation of scientists who are either terrible researchers, or are just recycling the already known.

Excuse me? Were they asserting that they can reconstruct monthly average temperatures 100,000 years ago from proxy data?
I want some of what they’re smoking.
This sounds like a classic high frequency vs low frequency data error, turned into a paper. I wouldn’t expect that 100,000 year data to be accurate to the year, let alone the month. I would further have to question the error bars — how, exactly were these computed?
Finally, when one refers to “the models” what models are they talking about? To the best of my recollection, we don’t have any models that can reconstruct even the approximate pattern of warming and cooling over the Pleistocene ice age including the shifts from 22-26 ky cycles to 41 ky cycles to 90-100 ky cycles and the associated significant deepening of the glacial trough:
http://upload.wikimedia.org/wikipedia/commons/6/60/Five_Myr_Climate_Change.png
let alone the last 65 million years (scroll down a bit to see). Milankovich is the usual assumption, but it has a very hard time functioning as a sufficient explanation, especially given:

Constructions of this kind are common. However, they assume that ice volume is driven by changes in insolation, and such data therefore cannot be used to establish the existence of such a relationship.

For once in the Wikipedia page, this is stated up front. A model is required to transform the proxy data obtained into an estimate of global temperature such as this graph, or the graph(s) shown above (which just reprint the usual Vostok ice core data). That model makes assumptions about synchronicity, how e.g. ice volume can be related to sedimentation rates, how ice core bubbles trap gases, how much diffusion occurs between adjacent layers over 100,000 year plus time intervals (note well the smoothing of the Vostok curves as they go into the more distant past!) and above all, the causes of the glacial cycle, e.g. Milankovich periodicities that can be fit to the data.
One cannot, then, use the data to prove that Milankovich cycles are the proximate cause of the Pleistocene glaciation. If I have noisy data and fit it to a quadratic model, I cannot use the quadratic model curve to prove that the noisy data was quadratic. It’s then a self-fulfilling prophecy.
So I’m not certain what the top article is really trying to accomplish with its comparison. Is it asserting that the models for geological time climate change are inadequate to explain the data? Of course they are — everybody knows that. Are they asserting that such already inadequate models as exist “might be” sufficiently accurate that we can resolve late-20th-century-possible-CO_2-driven warming from garden variety natural climate evolution? Don’t make me laugh. We can’t even reconstruct or explain the last 20,000 years with a believable ab initio physical model, let alone the last 100,000, 600,000, 3.5 million, 5 million, 25 million. We have little more than fond hopes of ever doing so, as the time resolution of the 25 million year data might be no better than the time frame of the entire Holocene — radiometric dating gets increasingly imprecise as one goes back in time, good to centuries, thousands of years, even tens of thousands of years when one gets way back there.
All we can say is that it is reasonably probable that the last interglacial was both on average and in marginally resolvable bursts warmer than this interglacial, in particular the present. Even in this interglacial:
http://upload.wikimedia.org/wikipedia/commons/c/ca/Holocene_Temperature_Variations.png
it is highly improbable that the present is the warmest period in the Holocene — again the figure caption quite honestly indicates that the black curve and the various colored curves have highly limited temporal resolution — smoothed to 300 years! — and the wide range of the different proxies strongly suggests that the probable standard error in even the 300 year smoothing is often/usually at least 0.5 C. This means that the actual high resolution inferred temperature excursions are at least the square root of the autocorrelation time divided into 300 times larger. If we assume a dominant/shortest autocorrelation time of perhaps 10 years, the actual warmest decades were probably as much as 2-3C warmer than the black curve, although there were equally probably decades that were this much colder — the underlying data does not look terribly synchronous. Again, one has to be careful to completely ignore the high resolution data spliced onto the ends as “the present” as those single year data points or decadal trends cannot meaningfully be compared to any part of 300 year windowed data (which, I will point out, is twice as long as the entire thermometric record).
The only useful information in the article above is that in previous interglacials, sea levels were 10 to 20 meters higher than they are now. That is data that is a) difficult to argue with, as it is direct observational data that can be confounded only by profound changes in ground level that one can relatively easily determine independently and correct for (and which are accompanied by commensurate swings in the ice sheet, which are also quite soundly recorded by proxy data, and of course by the radiometric data). In a sense, this renders the issue concerning models moot, if they weren’t already. As the top article notes, one way or another sea levels can go up 10 to 20 meters above their current level in an interglacial, without carbon dioxide, and, since we have no functional models that can explain the timing or severity or detailed evolution of the glacial/interglacial cycle in the first place, with or without CO_2, it is pointless to assert that there is some sort of “cap” on the currently observed climate state that cannot or would not be exceeded without increased CO_2.
This does, in a Bayesian sense, reduce the probability that the current warmth is strictly due to increased CO_2. I could formulate a theory such as “prayer works to cure cancer”. I could have a very serious physical model for an all-powerful God who could, if they wished, cure cancer in any individual or prevent cancers from ever occuring, but who chooses to actually refrain from doing so unless petitioned by prayer. I could then easily go out and find a dozen people who had cancer and who prayed and who were cured. Indeed, I might well find that nearly all of the people whose cancer went into remission or who survived for 10 years after surgery or other therapies prayed for a cure at one time or another. I could present this as powerful evidence that prayer works to cure cancer!
Except that it isn’t. One can count so very many flaws in this (common enough) religious argument. But the biggest difficulty is that there is no control group, and no double blind experiment, and no effort to even do proper epidemiological work on broad data to determine how prayer alters a baseline non-prayer-based survival rate. The existence of a large group of humans who did not pray (but whose cancer was cured anyway) is, in fact, evidence against the hypothesis. The demonstration that a suitable non-praying population that has a survival rate indistinguishable from an equally suitable praying population within their mutual standard errors would actually be strong evidence of the exact opposite — that whether or not God does or does not exist (Bayesian prior number one), whether or not God can or cannot cure cancer (Bayesian prior number two), it is actually extremely unlikely that God uses “I was prayed to for a cure” as the criterion for acting to cure cancer, if indeed God ever acts to cure cancer at all.
So the good thing about the geological record of the climate is that functions, or rather should function, as a sort of control group to confound assertions that greatly exceed the range of reasonable inferences supported by the data. When the daily high temperature outside in Durham, NC on any given calendar day of the year can fluctuate by an easy 20 or 30 C (depending on the time of year) according to the historical record, it isn’t really fair to state that just because the weather has been nice and comparatively cool for two weeks (or, in the current case, an entire summer) that a sudden warming is evidence for anything at all. “Random chance” (or if you prefer, entropy in the system associated with our lack of its precise state or time evolution) can easily explain it without any need or possibility of asserting a specific proximate cause.
This is why Mann’s work was so important to the IPCC, so important that it became cover art. Humans actually are pretty good at doing Bayesian statistics in their heads. If today’s temperatures are within spitting distance of MWP, RWP, or Holocene Optimum temperatures, if previous interglacials were even warmer than this one for reasons utterly beyond human control since humans had not, properly speaking, evolved yet, certainly not in any significant numbers, it becomes significantly less likely that the present requires some special explanation because it is in some sense “unusual”. That doesn’t mean that there might not be some special explanation, only that its logical or mathematical necessity becomes easy to doubt, and the predictions made on the basis of that special explanation are substantially “weaker” (less likely to be correct) than they would be if there was a fluctuation that is actually far out of the range of those observed in the past temporally synchronized with the special explanation. Mann — as apparently suggested by some of his peers — managed to find a data model that erased the MWP and LIA, rendering the past behavior smooth enough to fool a gullible public, including a gullible public of scientists who should have known, and done, better once it became clear which way climate funding cookie was crumbling.
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OK, obviously a problem for Mr. Moderator. Does WUWT no longer permit embedded links to figures? That’s gonna suck…

Since this low-CO2 global warming occurred entirely naturally, there is no evidence that global warming during the present interglacial is unnatural or man-made.

No, you can’t really say it this way. You can say that the current warming is within the range of naturally occurring conditions, based on historical data. Absence of human influence in the past doesn’t remove the possibility of it happening now.

Dr. Brown:
Milankovitch Cycles reproduce well the strength and duration of each interglacial at least since the switch in periodicity which you cite. The weak interglacials, like those of MIS 7 and 9, are reflected in orbital and rotational mechanics.
Please see Figure 1 in this link:
http://www.readcube.com/articles/10.5194/cp-6-31-2010
However, predicting the duration of the Holocene is complicated by the pronounced cooling trend of the past ~3300 years, which if extrapolated would get us back to glacial conditions in a few more thousand years. Based upon Milankovitch Cycles, however, the Holocene could be another multi-precession-cycle interglacial, like those of MIS 11 and 19, which would be good news for humanity, even if it meant some melting of the Greenland Ice Sheet. The southern dome is unlikely to melt completely, as in those prior two interglacials, because the Holocene has been quite a bit cooler.
Every interglacial is unique, so the lesser warmth of the Holocene may mean it ends sooner than the eccentricity cycle would suggest.
The onset of NH glaciation has indeed been modeled, and the results accord well with observations and proposed explanations. To take but one example:
http://www.sciencedirect.com/science/article/pii/S0012821X05004048
Final closure of Panama and the onset of northern hemisphere glaciation
Abstract
The Greenland ice sheet is accepted as a key factor controlling the Quaternary “glacial scenario“. However, the origin and mechanisms of major Arctic glaciation starting at 3.15 Ma and culminating at 2.74 Ma are still controversial. For this phase of intense cooling Ravelo et al. [1] [A.C. Ravelo, D.H. Andreasen, M. Lyle, A.O. Lyle, M.W. Wara, Regional climate shifts caused by gradual global cooling in the Pliocene epoch. Nature 429 (2004) 263–267.] proposed a complex gradual forcing mechanism. In contrast, our new submillennial-scale paleoceanographic records from the Pliocene North Atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation (NHG), since it was linked to a 2–3 °C surface water warming during warm stages from 2.95 to 2.82 Ma. These records support previous models [G.H. Haug, R. Tiedemann, Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermohaline circulation, Nature 393 (1998) 673–676. [2]] claiming that the final closure of the Panama Isthmus (3.0– ∼2.5 Ma [J. Groeneveld S. Steph, R. Tiedemann, D. Nürnberg, D. Garbe-Schönberg, The final closure of the Central American Seaway, Geology, in prep. [3]]) induced an increased poleward salt and heat transport. Associated strengthening of North Atlantic Thermohaline Circulation and in turn, an intensified moisture supply to northern high latitudes resulted in the build-up of NHG, finally culminating in the great, irreversible “climate crash” at marine isotope stage G6 (2.74 Ma). In summary, there was a two-step threshold mechanism that marked the onset of NHG with glacial-to-interglacial cycles quasi-persistent until today.

The sea level rise clinches it. And there is simply no way of knowing how non-intervention by us would have played out anyway . Therefore any deduction to the effect that an unexpected (why?) temp rise must be due to our contribution just doesn’t do it conclusively . RGB – brilliant as always. Cogent, incisive and eloquent.