Study: Tree rings can miss climate events UNIVERSITY PARK, Pa., Feb. 6 (UPI) -- Using tree rings to measure ancient climate events may underestimate the climate cooling effects of volcanic eruptions, U.S. researchers say. Scientists at Penn State say this is because large enough temperature drops can lead to greatly shortened or even absent growing seasons as reflected in tree rings. "We know these tree rings capture most temperature changes quite well," Michael Mann, professor of meteorology and geosciences, said in a university release Sunday. But the problem appears to be in their response to the intense short-term cooling that occurs following a very large volcanic eruption. Trees create unique rings each year that often reflect the weather conditions that influenced the growing season that year, researchers said. The problem is that these trees are so close to the threshold for growth, that if the temperature drops just a couple of degrees, there is little or no growth and a loss of sensitivity to any further cooling. In extreme cases, there may be no growth ring at all," Mann said. If no ring was formed in a given year, that creates a further complication, introducing an error in the chronology established by counting rings back in time. The potential absence of rings in the first one to three years following an extreme volcanic eruption can decrease the accuracy of ancient climate history reconstruction, researchers said.