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El Niņo and global warmingIs there a connection?
Normally the West Pacific is moist. Warm air rises over there and
decends in the East Pacific. This is the Pacific Walker Cell.
Over the equator an Easterly wind blows. Together with Southerly winds
along the Chilean and Peruvian coasts this causes upwelling of colder
water. Most years around Christmas some warmer water appears along the
Ecuadorian and Northern Peruvian coasts. This phenomenon was called El Niņo
(the boy-child) by the local people. Every 2 - 7 years the warming of the water
in the East Pacific is much more widespread, with dramatic (local, but also
larger scale) consequences. This phenomenon is referred to in the literature
as ENSO (El Niņo / Southern oscillation), or just the initial name of the local
people of Peru: El Niņo.
2. Events in the past
In the past some dramatic weather incidents took place in which El Niņo may have
played a role in. A notorious example is a devastating drought in India and
Australia in the years 1789 - 1792. In these years there was a monsoon failure
in South Asia. Millions of people perished in India in the famines which followed.
In the records the El Niņo of 1791-92 is bookmarked as "very severe", probably
about as strong as the 1982-83 and 1997-98 events.
Now the subject is addressed from three angles:
3. Looking at El Niņo from three angles
3.1. The impacts of El Niņo
As mentioned in the introduction, El Niņo is accompanied by shifts in the so called
Walker cell circulations over the equatoral part of The Earth. Two circulation
cells can be distinguished: The Hadley cells and the Walker cells.
If one compares the 1982-83 and 1997-98 El Niņo's in both cases there were droughts
in Indonesia and floods in Peru and Ecuador. But there were also differences.
The biggest differences were over Australia and Eastern Africa. In 1982-83 East
Africa was dry (due to subsiding air), while it was very wet at the end of 1997
(An eightfold of normal rainfall in Mombasa, a clear signal of convective activity).
At the start of 1998 NE Australia was deluged, while in 1982-83 droughts dominated
It is striking that the Monsoon over India was hardly affected by the 1997-98 El Niņo. I will come back on this at the end.
3.2. El Niņo and global warming
Now an interesting subject for further research arises. Is there a connection between the frequency and intensity of El Niņo and possible global warming? A first thing one can do is looking at the records, of which the qualitative records are quite long - going back to the conquest of the Inca Kingdom by the Spanish in the early 16th century.
Looking at these records reveils episodes with severe El Niņo's and less severe
El Niņo's: Very active periods were around 1580, the 1720-ties, around 1790,
1880-ties and 1890-ties, and after 1982-83 the 1990-ties.
However: This doesn't prove that there isn't a possibility of "passing a critical
treshold" boyond which a sort of switch to an other regime in terms of El Niņo
frequency and/or severity might be possible.
The authors of the article correctly point out that there are still processes not well understood, such as cloud feedback, which might change the found results from the model work.
A recent publication at the KNMI site points in the direction that there is no correlation between the temperature on Earth and the activity of the El Niņo cycle. (ref. 3)
Concluding: Up to now no connection between global warming and El Niņo has been found. The most recent publication points in the same direction: No link with global warming.
3.3. Changing impacts of El Niņo
A last interesting question is the question whether the effects of El Niņo themselves
could change as well in an event of global warming. In this case a recent publication
in Science (ref 2.) puts some more light on it.
One of the possible explanations: The warming of the Eur-Asian continent provides so much enhancement of the Monsoon, that it offsets possible El Niņo effects. It is known that the snow cover of central Asia (Tibetan plateau) in spring has an influence on the Indian Monsoon, especially its timing.
Concluding: This example shows that indirect effects of El Niņo may change to quite an extend from what was seen in the past in case of a certain degree of global warming.
1. A. Timmermann, J. Ohberhuber, A. Bacher, M. Esch, M. Latif and E. Roeckner
2. K.K. Kumar, B. Rajagopalan, M.A. Cane
3. Sjoukje Yvette Philip
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