Climate change leaves mark in U.S. tree rings

July 22nd, 2011  |  by  |  Published in Research News

line graph showing the amplitude of El Nino over 1000 years

Towering trees on the mountain slopes of the Southwest United States respond to the beat of El Niño. The rings in their trunks give a continuous history of variations in El Niño intensity over the past 1,100 years, providing information that could improve climate models and their prediction of how El Niño will change with global warming, scientists at the International Pacific Research Center say.

IPRC postdoctoral fellow Jinbao Li, University of Hawaiʻi at Mānoa Professor of Meteorology Shang-Ping Xie and their international colleagues found that wider rings resulting from wetter winters and narrower rings indicative of drought years match both 150 years of sea-surface temperature records and isotope concentration indicators of warm El Niño and cool La Niña years in Pacific corals.

Tree on mountain slope in Southwest United States

Trees have the advantage of providing a longer historical record, the scientists report in the May 6, 2011 issue of Nature Climate Change. They indicate that El Niño has been highly variable, with decades of strong El Niño events (the strongest occurring since the 18th century) and decades of little activity (the weakest during the Medieval Climate Anomaly in the 11th century).

Differing levels of El Niño activity are related to long-term changes in Pacific climate, which swings between warm and cool phases lasting 50–90 years each; El Niño and La Niña events were more intense than usual during warm phases.

“Since El Niño causes climate extremes around the world, it is important to know how it will change with global warming,” says Xie. Current models differ in their projections; the tree-ring data offer key observational benchmarks for evaluating and perfecting the models.

This research was funded by the National Science Foundation, National Oceanic and Atmospheric Administration, Japan Agency for Marine-Earth Science and Technology, National Basic Research Program of China and the National Natural Science Foundation of China.

Read the abstract in Nature Climate Change.

Tree rings also provide evidence of climate change following the eruption of Thera on Crete. Read more.

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