A history lesson from Tasmania
News stories about global climate change have recently included temperature histories that extend back for about a thousand years, thanks to the efforts of such researchers as the University of Virginia’s Michael Mann and colleagues. These long-term temperature histories are made up in large part from tree-ring records, which reflect the climate the trees experienced during their annual growth period (primarily summer).
The tree-ring records derive information not only from living trees, but also from trees that are long dead but whose wood has been preserved either naturally (for instance in dry climates) or from their historic use in building material. As more of these relict pieces of wood are found, the temperature history can be pushed back further and further.
Recent work published by E.R. Cook and three Columbia University colleagues describes a 3,600-year history of warm-season temperatures based on tree-ring records from the Australian island of Tasmania. What they have found is very interesting. Though there is no overall trend in the temperature history, both long-term and short-term changes are obvious.
This long-period temperature history can serve as a valuable lesson in climatology. At the end of the record, temperatures stood at their historical maximum levels after a rapid rise lasting about a century and a half. If that were all you had to go on, you might think the world was heading to hell in a hand basket.
But if you look only at the data for the next 50 years, you're likely to think another ice age must be just around the corner! And if you look at the entire record at once, what you see is that the temperature variation around the year 0--the one that had you believing the weather had turned truly wacky and was undoubtedly a sign of the apocalypse--is just another blip of the region’s temperature heartbeat. In the long term, there was nothing unusual about it at all.
It has often been said that those who are not familiar with history are apt to repeat it. Nowhere does this seem to be more true than in today’s climate hysteria. Since our illustration ends with the temperatures reaching another high point after about a century and a half of rapid warming, many believe the apocalypse is upon us. If only we could lift our hand off Figure 1 and uncover the next 1,000 years, many of these fears could be alleviated. But until then, perhaps this Tasmanian history lesson will be of some comfort.
According to Nature magazine, University of Virginia environmental sciences professor Patrick J. Michaels is probably the nation’s most popular lecturer on the subject of climate change. Michaels is the author of Sound and Fury: The Science and Politics of Global Warming.
Cook, E.R., et al., 2000. Warm-season temperatures since 1600 BC reconstructed from Tasmanian tree rings and their relationship to large-scale sea surface temperature anomalies. Climate Dynamics, 16, 79-91.