The World Was Warmer

Dendrochronology

Dendrochronology (Photo credit: fdecomite)

I have been criticizing the Global Warming advocates of making exaggerated claims beyond what the data might warrant, but now I suppose I ought to take on the other side. I am referring to the article I read in the Daily Mail titled Tree-ring study Proves that Climate was Warmer. In fact, from what I read, the study does no such thing. You cannot, in fact, prove what the temperatures were a thousand years ago unless someone invents a time machine and takes thermometers into the past to measure them.

How did the Romans grow grapes in northern England? Perhaps because it was warmer than we thought.

A study suggests the Britain of 2,000 years ago experienced a lengthy period of hotter summers than today.

German researchers used data from tree rings – a key indicator of past climate – to claim the world has been on a ‘long-term cooling trend’ for two millennia until the global warming of the twentieth century.

This cooling was punctuated by a couple of warm spells.

These are the Medieval Warm Period, which is well known, but also a period during the toga-wearing Roman times when temperatures were apparently 1 deg C warmer than now.

They say the very warm period during the years 21 to 50AD has been underestimated by climate scientists.

Lead author Professor Dr Jan Esper of Johannes Gutenberg University in Mainz said: ‘We found that previous estimates of historical temperatures during the Roman era and the Middle Ages were too low.

‘This figure we calculated may not seem particularly significant, however it is not negligible when compared to global warming, which up to now has been less than 1 deg C.’

In general the scientists found a slow cooling of 0.6C over 2,000 years, which they attributed to changes in the Earth’s orbit which took it further away from the Sun.

The study is published in Nature Climate Change.

It is based on measurements stretching back to 138BC.

The finding may force scientists to rethink current theories of the impact of global warming

Professor Esper’s group at the Institute of Geography at JGU used tree-ring density measurements from sub-fossil pine trees originating from Finnish Lapland to produce a reconstruction reaching back to 138 BC.

In so doing, the researchers have been able for the first time to precisely demonstrate that the long-term trend over the past two millennia has been towards climatic cooling.

I suppose that I should take into consideration that this is an article intended for a popular audience on a newspaper’s website and I am sure the authors of this study were more nuanced in the papers they wrote. Still, a more accurate headline might read “Study based on assumptions on the relation of tree-rings to temperature and climate infers that Europe, and possible the entire world was warmer in the past”. But, maybe they would have trouble fitting all that in.

The study seems to be a very extensive one and considering that there are other lines of evidence that show a warmer Earth at these times, the Romans growing grapes in Britain and the Vikings being able to colonize Greenland and Vinland, I really don’t have any doubt that their conclusions are accurate. I would like to emphasize, however, how tentative any such studies actually are.

By the way, if the Earth really is in a long term trend toward cooler weather, should we be worried about a new ice age? As I have said before, I would be a lot more worried about global cooling than I would about global warming. After all, the glaciers weren’t that far north of where I am sitting during the last ice age.

 

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