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El Nino’s Altered Behaviour may Be Due to Global Warming

by Medindia Content Team on  December 26, 2007 at 2:57 PM Environmental Health   - G J E 4
El Nino’s Altered Behaviour may Be Due to Global Warming
Researchers have suggested that the climatic event know as "El Nino", which occurs along the Peruvian coasts, is being affected by global warming, thus changing its observed behaviour.

Literally meaning "Baby Jesus", El Nino was given its name because it happens at the time of Christmas.
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Resulting from a series of interactions between the atmosphere and the tropical ocean, El Nino induces drought in areas that normally receive abundant rain and, conversely, heavy rainfall and floods in usually arid desert zones.

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Scientists term this phenomenon a "quasi-cyclic" variation because its periodicity, which varies from 2 to 7 years, shows no regular time pattern.

Though research conducted over the past 25 years, by oceanographers, climatologists and meteorologists has much improved knowledge on the mechanisms generating an El Niño event, it is not known if the intensity and frequency of the event is susceptible to modification in a situation of global warming.

For the research on this phenomenon, several geochemical factors contained in a drill core sediment sampled from 80 m depth under the Bay of Mejillones, in northern Chile, were determined.

Analysis of breakdown byproducts from diatoms, unicellular planktonic algae, yielded an accurate trace of this region's trends in sea surface temperature between 1650 and 2000. These samplings confirmed that the decrease in ocean temperature observed from 1820 affected the whole Pacific seaboard, from central Chile up to the North of Peru.

Complementary analyses on certain minerals contained in the sediment samples confirmed that these minerals were transported by the winds from the continent. Therefore the reinforcement of such prevailing winds, the trade winds, would have favoured the rise of colder waters up from deeper reaches, along the Pacific coasts of South America, by pushing the ocean surface layer westwards.

The new hypothesis that the researchers postulate suggests that, in a situation of climate warming, the large continent-ocean temperature (and hence thermal) contrast would be responsible for this accentuation of the trade wind regime.

The long-term persistence of a substantial temperature difference between ocean and continent would have caused an intensification of the prevailing winds. Then by pushing the surface water towards the west, these winds would have induced cooling of the coastal waters, changing the normal feature of the El Niño regime which is a warming of the waters.

According to the research, between the end of the Little Ice Age and the beginning of the global warming attributable to human activities, the ENSO regime was modified.

Historical climatology studies founded on chroniclers' accounts and descriptions of floods caused by these El Niño events also showed an abrupt change, around 1820, in the ENSO system along Pacific seaboard of South America.

Since the beginning of the 19th Century, in other words the final phase of the Little Ice Age, the characteristic feature of El Niño events was abnormal rainfall, both in central Chile during the southern winter and on the northern coast of Peru during the subsequent southern summer.

These results as a whole emphasize the complexity of the interactions at work between the global-scale climate changes, the diverse behaviour of the ENSO system and regional climate changes.

Source: ANI
KAR/M
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