Recent El Ninos Unlikely To Be Caused By Past Warming Trend

March 09, 1998

The global temperature increases this century are unlikely to be the cause of the spate of El Niño events during the 1990s, according to CSIRO scientist Dr Rob Allan.

"We know that El Niño tends to occur every two to seven years,’ says Dr Allan.

‘I have found two additional longer climatic fluctuations linked with El Niño: one occurs every eleven to thirteen years; the other, every fifteen to twenty years,’ says Dr Allan, from the CSIRO Division of Atmospheric Research.

‘These climatic fluctuations have probably occurred for thousands of years,’ says Dr Allan.

‘This makes me think that the gradual warming we’ve seen around the globe this century is unlikely to be the cause of the recent series of El Niño events,’ says Dr Allan.

‘The dominant influences governing the strength and occurrence of El Niño are the three climatic fluctuations and other natural climatic variations,’ says Dr Allan.

‘I know my results will add to debate in the scientific community about the behaviour of El Niño,’ says Dr Allan.

To reach his conclusion, Dr Allan analysed global atmospheric pressure and sea-surface temperature data collected during the past 125 years from almost seven hundred land locations and from numerous ship measurements.

Dr Allan’s research marks a major advance in understanding the nature and structure of El Niño and is an important step towards resolving the physical mechanisms that give rise to the El Niño cycle. The research will also help establish what influence the greenhouse effect might have on El Niño.

‘Agricultural scientists are keen to explore the potential for using this new understanding of El Niño to improve farm management strategies to deal with drought and floods,’ says Dr Allan.

Dr Allan recently returned from an eight month visit to the Hadley Centre at the United Kingdom Meteorological Office, where he worked with prominent British scientists tracking down and analysing extensive climatic records from a wide range of sources.

‘One of the more interesting records I found was a dog-eared exercise book containing nineteenth century weather reports compiled by British missionaries in Uganda,’ says Dr Allan.

CSIRO is now running climate models to assess likely future changes to El Niño caused by increasing levels of greenhouse gases such as carbon dioxide. The climate models, which are run on a powerful supercomputer, incorporate the behaviour of the oceans and the atmosphere, which are crucial to the formation of El Niño. Model simulations show that El Niño events are features of climate that can be expected to continue in future under greenhouse conditions.

Dr Allan and colleagues recently published an atlas featuring global historical atmospheric pressure and sea-surface temperature maps detailing every El Niño event since 1871.
-end-


CSIRO Australia

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