[NEW DELHI] Global warming may increase the frequency of a type of El Niño linked to devastating droughts over India, new research shows.
El Niño, a periodic warming of Pacific Ocean waters, takes two forms — the eastern Pacific El Niño and its more severe central Pacific counterpart, which emerged in the late twentieth century and is already known to cause drought (see Scientists solve riddle of El Niño and Indian monsoon).
Sang-Wook Yeh and colleagues from the Korea Ocean Research and Development Institute analysed a set of climate models to compare the frequencies of both kinds of El Niño under projected end-of-century global warming scenarios.
They conclude in Nature this week (24 September) that the number of central Pacific El Niño events could increase by as much as five times under the influence of global warming.
This could greatly impact the global climate, leading to increased severe drought over India, they say.
"The results described in this paper indicate that the global impacts of El Niño may significantly change as the climate warms," says Yeh.
Until the 1970s, the eastern Pacific Ocean waters warmed during an El Niño. But after the 1980s, the new type of El Niño emerged in which warming occurred in the central Pacific Ocean.
Its frequency has rapidly increased. There have been seven central Pacific El Niño events in the past two decades, compared to 32 eastern Pacific events since 1850.
The period during which the central El Niño emerged is "documented as the time when a climate shift or a global change has occurred", Ashok Karamuri, senior research scientist at APEC Climate Center, Korea told SciDev.Net.
During global warming, sea surface temperatures heat more rapidly than waters in deeper layer, disrupting and shifting of the boundary layers between warm and cold waters and ocean currents, giving rise to new circulation patterns, says Karamuri, whose team first described the emergence of the central Pacific El Nino.
Bhupendra Nath Goswami, director of Indian Institute of Tropical Meteorology, Pune, cautions against drawing conclusions based on current climate simulation models as these still need to be refined to remove inaccuracies. "Conclusions based on this ensemble are not highly reliable," he told SciDev.Net.
Nature 461, 511 (2009)