Here’s an interesting story about a group led by University of Arizona scientists studying jet stream position using tree ring analysis. By looking at the density of wood produced late in the growing season, the scientists were able to produce a long history of high-summer jet stream locations dating back to 1725. This time series showed that since the 1960s there have been some changes in how the jet stream shifts, taking more extreme positions than in previous decades.  You can read more about this at

Valerie Trouet takes a pencil-thin core from an old Bosnian pine (Pinus heldreichii) growing on Mount Olympus in Greece. (Photo: Greg King © 2010)