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Nature 407, 989-993 (26 October 2000) | doi:10.1038/35039597; Received 1 February 2000; Accepted 9 August 2000

Frank E. Urban1, Julia E. Cole2,3 & Jonathan T. Overpeck1,3

Department of Geological Sciences/INSTAAR, Box 450, University of Colorado, Boulder, Colorado 80309, USA

Department of Geological Sciences/INSTAAR/PAOS, Box 450, University of Colorado, Boulder, Colorado 80309, USA

Present addresses: Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA (J.E.C.); Institute for the Study of Planet Earth/Department of Geosciences, University of Arizona, Tucson , Arizona 85721, USA (J.T.O.).

Correspondence to: Julia E. Cole2,3 Correspondence and requests for materials should be addressed to J.C. (e-mail: Email: jcole@geo.arizona.edu). The bimonthly Maiana delta 18O record is available at http://www.ngdc.noaa. gov/paleo/pubs/urban2000.

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Today, the El Niño/Southern Oscillation (ENSO) system is the primary driver of interannual variability in global climate, but its long-term behaviour is poorly understood. Instrumental observations reveal a shift in 1976 towards warmer and wetter conditions in the tropical Pacific, with widespread climatic and ecological consequences1, 2, 3. This shift, unique over the past century4, has prompted debate over the influence of increasing atmospheric concentrations of greenhouse gases on ENSO variability5, 6, 7. Here we present a 155-year ENSO reconstruction from a central tropical Pacific coral that provides new evidence for long-term changes in the regional mean climate and its variability. A gradual transition in the early twentieth century and the abrupt change in 1976, both towards warmer and wetter conditions, co-occur with changes in variability. In the mid–late nineteenth century, cooler and drier background conditions coincided with prominent decadal variability; in the early twentieth century, shorter-period (approx2.9 years) variability intensified. After 1920, variability weakens and becomes focused at interannual timescales; with the shift in 1976, variability with a period of about 4 years becomes prominent. Our results suggest that variability in the tropical Pacific is linked to the region’s mean climate, and that changes in both have occurred during periods of natural as well as anthropogenic climate forcing.

via Influence of mean climate change on climate variability from a 155-year tropical Pacific coral record : Abstract : Nature.

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