This is a cross section of a white spruce that lived from 1441 to 1931. Its outermost rings, which are clearly thicker than the rings closer to the core, date from the 1880s to the early 1900s, and record the global trend of warming that began around the same time.
Prof. Gordon Jacoby, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York
Topic: Earth Science
Subtopic: Climate/Climate Change
Keywords: Climatic changes, Global warming, Tree rings, White spruce