NAS NRC panel on temperature reconstructions has released its report.
The press release states
There is sufficient evidence from tree rings, boreholes, retreating glaciers, and other “proxies” of past surface temperatures to say with a high level of confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years, according to a new report from the National Research Council. Less confidence can be placed in proxy-based reconstructions of surface temperatures for A.D. 900 to 1600, said the committee that wrote the report, although the available proxy evidence does indicate that many locations were warmer during the past 25 years than during any other 25-year period since 900. Very little confidence can be placed in statements about average global surface temperatures prior to A.D. 900 because the proxy data for that time frame are sparse, the committee added. …
The Research Council committee found the Mann team’s conclusion that warming in the last few decades of the 20th century was unprecedented over the last thousand years to be plausible, but it had less confidence that the warming was unprecedented prior to 1600; fewer proxies — in fewer locations — provide temperatures for periods before then. Because of larger uncertainties in temperature reconstructions for decades and individual years, and because not all proxies record temperatures for such short timescales, even less confidence can be placed in the Mann team’s conclusions about the 1990s, and 1998 in particular.
The committee noted that scientists’ reconstructions of Northern Hemisphere surface temperatures for the past thousand years are generally consistent. The reconstructions show relatively warm conditions centered around the year 1000, and a relatively cold period, or “Little Ice Age,” from roughly 1500 to 1850. The exact timing of warm episodes in the medieval period may have varied by region, and the magnitude and geographical extent of the warmth is uncertain, the committee said. None of the reconstructions indicates that temperatures were warmer during medieval times than during the past few decades, the committee added.
Realclimate on the report:
However, it is the big picture conclusions that have the most relevance for the lay public and policymakers, and it is re-assuring (and unsurprising) to see that the panel has found reason to support the key mainstream findings of past research, including points that we have highlighted previously:
At Climateaudit on the other hand:
I’d characterize it more as schizophrenic. It’s got two completely distinct personalities. On the one hand, they pretty much concede that every criticism of MBH is correct. They disown MBH claims to statistical skill for individual decades and especially individual years.
However, they nevertheless conclude that it is “plausible” – whatever that means – that the “Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium”. Here, the devil is in the details, as the other studies relied on for this conclusion themselves suffer from the methodological and data problems conceded by the panel. The panel recommendations on methodology are very important; when applied to MBH and the other studies (as they will be in short order), it is my view that they will have major impact and little will be lefting standing from the cited multiproxy studies.
This should finally put an official end to the silliness that’s gone on for the last few years. I don’t doubt that McIntyre will continue to bloviate, but journalists especially now have no reason to give him any traction.
My reading of the summary of the report and parts of the text is that the NAS has rendered a near-complete vindication for the work of Mann et al.
Well, the report is out and it seems to be a fairly strong vindication of Mann et al. There is some more fuzzy language that will surely be seized apon by some but there is certainly nothing to support the allegations of errors, omissions and frauds that had been thrown around. The main conclusion is that many other studies support these same findings and that this is not a central issue in the present and future of climate change.