An international conference was recently held in Zakopane, Poland hosted by the Department of Quaternary Paleogeography and Paleoecology at the University of Silesia and the Institute of Geography and Regional Development at the University of Wroclaw. The meeting also served as the Annual Conference of the Association for Tree-Ring Research. Over 100 scientists gave presentations at the meeting, most were from Europe, although one presenter was from Penn State University and two others from the University of Missouri made the trip to present their research in Poland. The Association for Tree-Ring Research is a credible organization with no agenda that we know of regarding the global warming issue.

One presentation there was entitled “Climate variation (cycles and trends) and climate predicting from tree-rings”, and normally, we would be reluctant to feature conference presentations at World Climate Report. However, the work is an update of what the lead author recently published in The Holocene, the work is currently under review at an undisclosed scientific journal, and the authors have a history of publications in outstanding journals.

The work was conducted by three scientists from the Finnish Forest Research Institute and the University of Helsinki. They begin their piece noting that “The growth of Scots pine (Pinus sylvestris L.) is highly sensitive to June-July temperatures at the Finnish pine timberline. Exceptional preservation of pine wood and it accumulation in non-oxygen muddy bottoms of ice-cold lakes have made it possible to build a 7641 years long continuous tree-ring chronology.” Basically, the annual tree rings record information about the temperatures in Finland in the summer (warmer is better for the trees), and if the tree happens to fall into a nearby lake at the end of its long life, the wood is preserved for thousands of years. Timonen et al. recover the wood, measure the width of each ring, cross-date the samples, and with a huge amount of effort and statistical wizardry, they can recreate summer temperatures in Finland going back thousands of years – very clever, indeed. They note “The characteristics of this chronology, the distribution of the samples (on both sides of the present timberline) and the strong June-July have provided exceptional tools for dendroclimatic analysis and reconstructions.”

Are you ready to see over 7,500 years of summer temperatures from Finland? Figure 1 is the end product of their work, and the white line is the 100-year smoothed temperature values from the Scots pine reconstruction. The red and blue surfaces show the smoothed and highly stylized annual temperatures for the Northern Hemisphere (based on the work of others). At this scale, a case for recent warming can be made based on the tree-ring record, but the recent warming is paled by many past events including many red-hot summers in Finland 7,000 years ago. If nothing else comes from their figure, be keenly aware that climate always changes – flat line periods simply do not exist!

Figure 1. 7,500 year 100-yr smoothed reconstruction of Finnish summer temperatures (from Timonen et al., 2008).

The tree ring data in Figure 1 were smoothed using a 100-year sliding window; Figure 2 is for the last 1,300 years showing each summer and smoothings at the decadal, multi-decadal, centennial, and multi-centennial time frames. In describing the results, Timonen et al. write “The warmest and coldest reconstructed 250-year periods occurred AD 931-1180 and AD 1601-1850. These periods overlap with the Medieval Warm Period (MWP) and the Little Ice Age (LIA). The coldest and warmest of all reconstructed 100-year periods occurred AD 1587-1686 and AD 1895-1994, respectively.”  Read rest...

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