Mann et al. has a new paper out that again reconfirms that the MWP was not as pronounced or as high a warming period as today’s climate changes are bringing.
This is no longer surprising and is in close agreement with all other NH reconstructions that have been done, and all global reconstructions as well.
What is different about this one is that the reliance on tree-rings, and therefore the uncertainties and difficulties they impose, has been removed by using alternative sources of proxy data including marine and lake sediment cores, ice cores, and coral cores.
The authors write:
Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context. Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used, the conclusion can be extended to at least the past 1,700 years.
What also won’t be surprising will be the ad hominem attacks on Michael Mann and the knee-jerk dismissal of yet more inconvenient evidence that warming is happening, unusual and anthropogenic. I’m sure they will be many and immediate.
I have written before in length that regardless of what the MWP did or did not do, the case for anthropogenic global warming is very solid. While informative, the study of the past is neither explanatory of the present nor predictive of the future. The expectations and observations of today do not require a mild MWP to stand or fall and in fact the point has been made by many already that if indeed the MWP had shown a very high degree of variability that would be cause for more concern as it would suggest greater instability in the global climate and therefore greater vulnerability to human perturbations.
[Update: the paper can be found here -PDF-]