Based on data from a few carefully selected tree rings, dogmatic warmist scientists like to insist that the Medieval Warm Period really did not exist globally and was only a local North Atlantic phenomenon.
The climate, they tell us, was pretty much steady over the last couple thousand years – until man began to prosper a hundred years ago.
However, yet another new study, one by Michael Shawn Fletcher and Patricio Iván Moreno, has been published and adds more to the growing mountain of evidence that the Medieval Warm Period was indeed a global phenomenon. This in turn means that natural climate drivers are dominating the development of the climate, and not CO2.
Yeah, like we’re really surprised.
The authors did an analysis of pollen and charcoal from Laguna San Pedro, a small closed-basin lake located in the Andes of Chile. Their results reveal centennial-scale changes in vegetation, climate and fire regime since 1500 cal yr before present.
According to the study’s abstract, they found periods of relatively low summer moisture and increased fire activity between 1500–1300 and 1000–725 cal yr BP. The period 1000–725 cal yr BP (i.e. Medieval Warm Period) is characterised by remarkably rapid bulk sediment accumulation, from which they infer prolonged annual sedimentation resulting from a decrease in the duration of lake freezing under a warmer climate. Before the Medieval Warm Period, i.e. 1300–1000, they found relatively moist conditions during summer and low fire activity. After the Medieval Warm Period, from 725–121 cal yr BP, there was slow bulk sediment accumulation implying a cool and wet climate. Adios Hockey Stick!
The abstract concludes (emphasis added):
Our results suggest that the Medieval Climate Anomaly chronozone was relatively warm and dry, followed by a cool-wet climate during the Little Ice Age chronozone, before a substantial modification of the vegetation landscape by Europeans occurred in the mid 1800’s. The timing and direction of changes in the Laguna San Pedro record bear a striking resemblance to multiple independent tropical Pacific precipitation reconstructions, areas where precipitation is governed by the El Niño-Southern Oscillation (ENSO), and with the modern influence of ENSO over the climate in the region. We conclude that ENSO was the main driver of changes in growing season moisture in this part of the Temperate-Mediterranean Transition in south-central Chile over the last 1500 years.”
Here the authors lost it in the last sentence. I’m not at all convinced by their attribution to the ENSO, which is an internal oscillation occurring over annual and decadal scales. But the changes that the two authors have observed actually occur over decades, centuries and likely millenia. They really need to compare their results to solar and ocean cycle data, which today are readily available. Of course, they may not like what they find. But as scientists, they’ll surely put aside any prejudices that may exist.
If they do that, then they’ll reach a different conclusion. One thing is sure: the observed climate cycles have nothing to do with GHGs and man. That hypothesis can be fed to the shredder and dustbin.