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Human Versus Natural Causes of the mid-1970s Climate Anomaly
Published: April 27, 2009
Posted: May 18, 2009

Observations indicate there was a significant shift in the mid-1970s from cooler to warmer tropical Pacific sea surface temperatures (SSTs), part of a pattern of basin-wide SST anomalies with impacts that extended globally. The cause of these SST anomalies has been a topic of scientific debate in the climate research community. In a recent paper, scientists at the National Center for Atmospheric Research and the Program for Climate Model Diagnosis and Intercomparison at Lawrence Livermore National Laboratory analyzed observations and climate model simulations showing that the 1970s climate shift in the Pacific was a combination of warming due to human-produced greenhouse gases superimposed on what was likely an internally-generated natural decadal fluctuation of the Pacific climate system. Determining the relative roles of human influence versus naturally-occurring internal variability is important for understanding observed climate fluctuations and for the new field of decadal climate prediction. This new field will attempt to estimate regional climate anomalies over the next several decades with contributions from both inherent climate variability and external forcing from human activities.

Reference:  Meehl, G. A., A. Hu, and B.D. Santer, 2009: The mid-1970s climate shift in the Pacific and the relative roles of forced versus inherent decadal variability, J. Climate, 22, 780--792.

Contact: Anjuli Bamzai, SC-23.1, (301) 903-0294
Topic Areas:

  • Research Area: Earth and Environmental Systems Modeling

Division: SC-33.1 Earth and Environmental Sciences Division, BER


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