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New Study Led by William Paterson University Researcher Confirms Unprecedented Warming Trend in Central Asia

Davi (left) with colleagues on the Mongolian Steppe

--Researchers use tree-ring analysis to develop 1,000-year temperature chronology; find recent decades are the warmest period

--Results published in current issue of Quarternary Science Reviews

Researchers studying the rings of living and dead trees in remote areas of Mongolia and Central Asia have developed a millennium-length temperature reconstruction for the region that confirms that recent decades are the warmest period in the last 1,000-plus years.  The study, led by Nicole Davi, an assistant professor of environmental sciences at William Paterson University, appears in the current issue of Quarternary Science Reviews.

“Central Asia has very short and incomplete meteorological records, so our understanding of the climate system there is extremely limited,” says Davi, who is also an adjunct associate research scientist at the Tree-Ring Lab of Columbia University’s Lamont-Doherty Earth Observatory.  “Our new temperature reconstruction fills a void, and places the warming trend seen in the past few decades into a long-term context of the past 1,000 years.”

Tree-ring records (and other natural recorders of climate) are critical to the study of past climate events as well as what is possible in terms of temperature variability on timescales of hundreds and thousands of years. “Knowing what has happened gives us a baseline to understand what can happen in the future,” says Davi.

The research is based on an extensive collection of living and dead Siberian larch trees found at elevational treeline sites in north central Mongolia near Lake Hovsgol, where the dominant limiting factor for growth is temperature.  “This is one of the coldest regions in central Asia,” says Davi.  “The trees are extremely slow-growing and long-lived. In this harsh environment, trees can fall over and remain on the mountaintop without decaying for 800 to 1,000 years.  By using a combination of living and dead wood we can create millennial-length records of temperature.”

The research was conducted in Odor Zuun Nuruu, a very remote site in Northern Mongolia only accessible by horseback. After a three-day trek to reach the site, the team of international scientists and students worked to sample both the long-lived trees and dead logs using non-destructive hand drills (increment borers). Samples roughly the size of a pencil were removed from the living trees and sections were taken from dead trees. Most samples were then shipped back to the United States for processing and analysis. Davi and her colleagues have an ongoing collaborative research program with the Department of Forestry at the National University of Mongolia. “Their logistical and scientific support is essential for a successful field campaign and research program,” says Davi.

Davi and her co-authors found that seven of the 10 warmest individual years and five of the warmest 20-year periods occurred during the 20^th and 21^st centuries.  The most recent decades studied, 1986-2005, were the warmest period.  This warm period is also concurrent with a devastating and widespread drought that began in 1999 and resulted in mass livestock losses across the country.

The scientists were also able to gain a better understanding of the timing and spatial reach of a number of large volcanic events, about which very little is known. Through their tree-ring analysis, the researchers found evidence of significant impact from volcanic eruptions.  “Some past tropical volcanic eruptions were so explosive that they cooled average temperatures around the world, causing the trees in northern Mongolia to form very narrow rings,” says Davi.  Very narrow rings were found in the tree-ring record that correspond to known volcanic events in years AD 935 (Eldgja, Iceland), 1177 (Haku-San, Honshu, Japan, and Katla, Iceland), 1258 (likely Samalas, Indonesia), 1454 (likely Kuwae, Vanuatu), 1601 (Huaynaputina, Peru), 1783 (Laki, Iceland), 1884 (Krakatoa, Indonesia), and 1912 (Katmai, Alaska).

The other co-authors of the study are Drs. Rosanne D’Arrigo, Gordon Jacoby, and Edward Cook, Tree-Ring Laboratory, Lamont –Doherty Earth Observatory, Columbia University; Dr. Kevin Anchukaitis, Department of Geology and Geophysics, Woods Hole Oceanographic Institution; Dr. Baatarbileg Nachin, Department of Forestry, National University of Mongolia; and two doctoral students, Mukund Palat Rao and Caroline Leland, Department of Earth and Environmental Science, Columbia University.