Impact of increased CO2 on simulated ENSO‐like phenomena

Thomas R. Knutson, Syukuro Manabe

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The impact of a CO2‐induced global warming on ENSO‐like fluctuations in a global coupled ocean‐atmosphere GCM is analyzed using two multi‐century experiments. In the 4×CO2 experiment, CO2 increases by a factor of four in the first 140 years and then remains constant at 4×CO2 for another 360 years; in the control experiment, CO2 remains constant at 1×CO2 for 1000 years. The standard deviation of tropical Pacific SST fluctuations (7°N–7°S, 173°E–120°W; 2 to 15 year timescales) is 24% lower in the 4×CO2 experiment than in the control experiment; for the model's Southern Oscillation Index, a 19% decrease occurs, whereas for central tropical Pacific rainfall, a 3% increase occurs. An important feature of the control simulation is the internally generated modulation of variability on a multi‐century timescale, which is comparable in magnitude to the changes occurring with 4×CO2. We conclude that despite an order 5 K warming of the tropical Pacific, and order 50% increase in time‐mean atmospheric water vapor under 4×CO2 conditions, ENSO‐like SST fluctuations in the coupled model do not intensify, but rather decrease slightly in amplitude. This paper is not subject to U.S. copyright. Published in 1994 by the American Geophysical Union.

Original languageEnglish (US)
Pages (from-to)2295-2298
Number of pages4
JournalGeophysical Research Letters
Issue number21
StatePublished - Oct 15 1994

All Science Journal Classification (ASJC) codes

  • Geophysics
  • General Earth and Planetary Sciences


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