Curmudgeon -
The comparison is clearest in the third graph. "Zero" in that graph is the Holocene maximum temperature. In the paper they conclude that, with 0.7 degrees of warming between 1880 and 2000, the temperature had returned, at least, to the Holocene maximum by 2000. You can see that the maxima at 125,000 and 400,000 were only 0.5-0.7 degrees warmer than the Holocene maximum, yet sea level was 5 m or more higher than now. Conclusion: less than 1 degree more and we have the potential for 5 m or more of sea level rise. Other arguments, summarised in the article, indicate this could happen within this century.

Alice -
I didn't write the subheading, it was Editor: "Five metres of sea level rise in 89 years."
My article says "ice shelves disappear", not "ice sheets disappear".
Weather is chaotic, but that doesn't make climate (the long-term average) chaotic. Go learn more.
Uncertainty cuts both ways. What if things turn out *worse* than expected (as they are tending to do, actually)?
For evidence that human emissions of CO2 are the main cause of present warming, see my post http://betternature.wordpress.com/2010/12/08/still-warming/ .

malrob-
C02 was not the trigger for ice age warming, increase solar heating was the trigger and CO2 then amplified the resulting rise in temperature. This is well understood, see http://betternature.wordpress.com/2009/11/12/co2-lag-during-ice-ages/.
The anecdotal evidence you cite for MWP says only that parts of Europe were relatively warm. Mainstream consensus is that Medieval global temperature was not warmer than at present. Nor did it change by 4 degrees in 20 years. Sea level rate of change is quoted from Hansen.

Thanks Geoff

"Weather is chaotic, but that doesn't make climate (the long-term average) chaotic. Go learn more."

Shall do. Are you are claiming "long-term climate" is predictable? On what basis? Computer models? Established laws of climate change?

Why, for example, should the so-called standard climatological normal be a 30-year period, by WMO et al convention?

"Uncertainty cuts both ways. What if things turn out *worse* than expected (as they are tending to do, actually)?"

So-called Precautionary Principle, if that is what you are evoking here, has nothing to do with science. Is it more than a clever way of rationalising confirmation bias, prejudice? Whatever it is, it is not science.

As for future climate projections and/or "predictions", how is it that even peer-reviewed climate scientists now admit that: "strictly, the calibration and evaluation of climate model predictions is IMPOSSIBLE, as projections of climate change relate to a state never before observed?" (p2746)

Reference: Challenges in combining projections from multiple models, J. Climate 2010
http://www.iac.ethz.ch/people/knuttir/papers/knutti10jc.pdf

Furthermore, "there is little agreement on metrics to separate 'good' from 'bad' models". (page 2739)

"There is a concern that model development, evaluation and posterior weighting or rnaking are all using the same data sets," and so on.

So what do the modellers do? Mix them altogether and pray their biases, etc, cancel each other out. [Imagine if any other profession, such as medical research, acted in this way.]

You folk want a restructuring the entire global economy based on this kind of "evidence"?

Alice (in Warmerland)

Geoff Davies
look, I regret, your reassuring explanation answered none of my concerns, nor was it particularly relevent. The article has done immense damage to your own side.

Although I still have to go over this much vaunted paper, various "adjustments" seem to be required to make the record say what you want. This business about being back near the holocene maximum is highly doubtful and very strongly contested in the literature, as you know. It is far from clear we are even back near the medieval warming period peak - it is certainly not the case in Europe. Warmists have tried to contest that one by putting together dodgy multi-proxy analyses, only to have them fall over.

Therefore this business about comparing sea heights now and at the time you specified is almost certainly irrelevent until proven otherwise. Considerable work has been done on recent (slight) sea level increases. There was also a recent article on this site by a Cliff Oliver from the Uni of WA, who pointed out, with some authority, that this business about ice sheets collapsing is imposible. My suggestion is that you read it.

Curmudgeon-
I did address the question you raised, you've just shifted your ground in response. Your initial comment had a clear misconception: H&M have not argued that "present temperatures are higher" than any in the past. As you note, their data clearly show otherwise. The paper is about how much higher, and when. Now you're arguing about Holocene maximum and alleged MWP, which they do address but I didn't cover it in what is, after all, a summary.

You (and most others here) dismiss a major data set because you don't like the conclusion. You disparage it with phrases like "clever if rather obscure", "transparently ad hoc", and you make the usual insulting charge: "various "adjustments" seem to be required to make the record say what you want".

All of this *without* having read the paper itself, which includes extensive discussions of many issues concerning the reliability of data and interpretations.

At least Sniggid and others here just get on with their ad hominem slurs, without having to disguise them in pseudo-reasonable, pseudo-rational lectures.

How can anyone talk about pseudo rational anything, while actually referring to Hansen as an authority.

Any one who has been caught in such outrageous concocting & doctering of data as him, is hardly going to convince anyone other that the "true believer", or a fellow traveler.

Geoff

As with most of this pleading you accuse us of everything you are doing.

But having studied the material in a little more detail it occured to me what this is really about. Hanson is trying to revive this discredited idea of his of big increases in sea levels. I recall him peddling the idea of the ice sheets breaking up, as opposed to melting,to get the big increases he required in just a few decades. (Look at what Cliff Ollier wrote on this site.) But he had to abandon his big seas concept in favour of less than one metre increase, as that was all the IPCC would give him, in part because they ran into this problem of ice sheets taking much longer to break up break up than the few years he required.

Now Hanson's high sea levels are back, but from a different direction. Just ignore the data set everyone uses in favour of this other one, gloss over all the problems of relating ancient temperatures to modern ones, assume temperatures will go up a degree - big, big assumption - wave away all the problems about ice sheets breaking up, and you have catastrophically high sea levels.

And we're the ones ignoring inconvenient data?

This paper is not so much bad as very, very thin. Really Geoff, you should have spotted it as a piece of ad hocery the moment you saw it. Why bother us with it?