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.