[JoeFromSidney]

Take the year 1580, which left the narrowest growth ring — or none at all — in the California trees that University of Arizona scientist David Meko used to reconstruct a 1,000-year history of stream flow in the Sacramento River Basin, the source of much of the state's water supply.

Now isn't that interesting? Size of tree rings is caused by water availability, not by temperature. But what about all those narrow tree rings in Siberia?

[ApplegateRanch]

It depends upon the species of tree; its geographic location; and the agenda of the scientist studying it. ;-)