Is There a Connection Between El Nino and Global Temperatures?
by S. Fred Singer

Some climate model experiments suggest an increase in El Nino frequency, linked to a future greenhouse warming [1]. The computer simulation shows a warming trend near the surface in equatorial waters and a cooling trend in deeper layers, leading to a stronger thermocline. (The cooling is attributed to an inflow of colder water, in response to an intensified Hadley circulation.) The strongest surface warming is calculated to occur in the equatorial eastern Pacific, in accord with a physical picture [2] that posits the existence of a "thermostat" in the western Pacific, which keeps the high surface temperature there from rising further because of a cloud-albedo feedback [3].

On the other hand, a different physical model leads to strong upwelling in the eastern equatorial Pacific that could weaken the warming there, thereby strengthen equatorial winds, causing more upwelling and a net cooling in the eastern Pacific [4]. Such a feedback process would lead to La Nina-like conditions, eventually retarding global warming. Which picture is more nearly correct?

To investigate this disagreement empirically, one can ask: What happened in the eastern Pacific during the strong global warming of the first half of the century? We have therefore examined sea surface temperature (SST) data for five areas of the eastern tropical Pacific (ETP) [5]. These were kindly made available to us by Nick Rayner, at the request of Geoffrey Jenkins of the Hadley Centre of the U.K. Meteorological Office. We had noticed that a Met Office brochure (Nov. 1998, p.3) shows SST changes during 1871-1998 for the ETP off Peru in an area designated as Nino 3.4 (170-120W, 5N-5S) [6]. Quite apparent there was the dearth of temperature peaks between about 1920 and 1955, except for a rather moderate one around 1939.

When we plot running averages for the five sub-areas, we note that ETP/SST did not rise during the period 1910-1940 when the (IPCC) global average temperature (GAT) and tropical SST [7] showed a remarkable increase of nearly 0.4°C. In fact, in some sub-areas temperatures declined markedly. During the period 1940-1975, when global temperatures diminished, one can detect a slight increase in the ETP/SST. Between 1975 and 1980, however, the ETP/SST rose sharply, along with global average temperature. Since 1980, there has been a modest increase in the ETP/SST. During this latter period, weather satellite data showed a slight cooling trend for the tropical regions, whereas surface data showed a warming trend.

We find that ETP/SST, the sea-surface temperature of the eastern tropical Pacific, (an indicator of El Nino, according to computer models) shows no obvious correlation with GAT or with tropical SST as a whole; in fact, there appears to be an anti-correlation during the period of strongest global warming.. With the evidence on hand, we conclude that it is not possible to link a future global warming, from whatever cause, to an increase in frequency or intensity of El Ninos.

S. Fred Singer (July 16, 1999)
The Science & Environmental Policy Project .
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1. Timmermann, A., J. Oberhuber, A Bacher, M. Esch, M. Latif, and E. Roeckner. Increased El Nino Frequency in a Climate Model Forced by Future Greenhouse Warming. Nature, 398, 694-696, 1999.

2. Meehl, G.A., and W.M. Washington. El Nino-like Climate Change in a Model with Increased Atmospheric CO2 Concentrations. Nature, 382, 56-60, 1996.

3. Ramanathan, V., and W. Collins. Thermodynamic Regulation of Ocean Warming by Cirrus Clouds Deduced from Observations of the 1987 El Nino. Nature, 351, 27-32, 1991.

4. Cane, M.A., et al. Twentieth-Century Sea Surface Temperature Trends. Science, 275, 957-960, 1997.

5. Rayner, N.A., E.B. Horton, D.E. Parker, C.K. Folland, and R.B. Hackett. Version 2.2 of the Global Sea-Ice and Sea Surface Temperature data set, 1903-1994. Climate Research Technical Note. CRTN 74. Hadley Centre for Climate Prediction and Research. September 1996.

6. Rayner, N.A., private communication, January 1999

7. Bottomley, M., C.K. Folland, J. Hsiung, R.E. Newell and D.E. Parker, (1990) in Global Ocean Surface Temperature Atlas: "GOSTA", a joint project of the U.K. Met.Office and MIT. Is There a Connection Between El Nino and Global Temperatures?