The world was hotter for most of the past 10,000 years

and yet there is evidence it stayed frozen last 10,000 years

 

Mann's claim was for (depending on the paper) 400 years, up to 1000 years or so. For that period, the evidence is pretty solid that he was, in fact, correct, for the northern hemisphere, e.g., a compendium of proxy reconstructions shown here:



Those are all area-weighted averages, designed to reflect the average temperature of the globe. And they rely on a wide variety of proxies.

This newest paper takes an unweighted average of proxy records. The "temperature" graph is literally a count of the proxies. That's a weak analysis.

In the same vein, what's the standard error around this estimate? None was given. That's a bit of a red flag, isn't it? Don't scientific studies usually assess the uncertainty around the estimate?

Given that they had the proxies, why didn't they generate a geographically-weighted average? Take a look at the map. More than half the proxies are in Europe. Take a look at the chart of proxies. Does it look balanced, north to south? If you were to take that geographically weighted average, with a handful of proxies standing in for the majority of the globe's surface, this would yield very large standard errors around the estimated global average.

For that matter, what is the journal GEOGRAFIE • ROK 2011 • ČÃSLO 2 • ROČNÃK 116. That looks like some Slavic language. Have you ever heard of it before? Have you ever read a climate study from that journal before? I can't even track them down with Google. Now that's obscure. How do you people find stuff like this?

EDIT: Found it, it's "The oldest scientific journal in Czechia", published since 1895, included in the scientific indices since 2008. So that's how they found it. Any hint there that, possibly, the review might not have been as rigorous as in, say, a more mainstream or better-known science journal?

On balance, I think I'll stick with what the IPCC said in 2007 on reconstructions of holocene temperatures, available here:

6.5.1.3 Was Any Part of the Current Interglacial Period Warmer than the Late 20th Century? - AR4 WGI Chapter 6: Palaeoclimate

In a nutshell, there's good evidence that some areas at some times had temperatures higher than today. (And good evidence that some parts at some times were colder.) That's part of the whole Eurocentric "holocene thermal maximum". But, as far as they can tell, not the globe as a whole. On net, that seemed like a pretty even-handed analysis to me. They end with this:

" Current spatial coverage, temporal resolution and age control of available Holocene proxy data limit the ability to determine if there were multi-decadal periods of global warmth comparable to the last half of 20th century."

In other words, the data are just too thin to be able to say much, definitively, about that time period. Unless this most recent work actually uncovered significant new sources of information (and it didn't), then I don't see a compelling reason to believe this analysis (a count of proxies from some selected set, unweighted) over the IPCC summary.

 

This seems to be the journal website

ÄŒeská geografická spoleÄÂnost

and it's only in Czech not English. We could of course hope that the author would make an effort to get this work in a more visible journal. This would suggest that it had been reviewed by people familiar with the topic area. In the present instance, it is difficult to be sure of that.

I know, others might suggest that it would be 'censored' from the 'mainstream'. I wouldn't agree, but this enters the area of personal opinion.

The concern raised in #2 here was that high-latitude stores of reduced carbon argues against higher temps over the recent millennia. Lonnie Thompson's glaciology research does as well, and I've already suggested that people interested in this topic read about that.

Anyway, the thesis advanced in the paper cited here was that these proxies indicate extended periods when average T was 2 oC higher than preindustrial 1750 AD. That might be equivalent to a claim of 1 oC higher than currently. Whether the second claim would be regarded as a strong one probably depends on how precise one supposes those proxies actually are. I noticed that many of the proxies were based on pollen, and I know some folks who work in that field. I will hazard speaking for them, that 1 oC is 'pushing it'.

I would be remiss not to welcome mojo into the group of people who regard the concept of an average annual temperature as a meaningful concept. Also that proxies (including dendroecology) do provide useful climate information. Several prominent climate 'skeptics' do not accept one or both, and it is most welcome to see you leaving them behind.

 

It is settled and the world laughs at those like you.