BACK	ENVIRONMENT: Global Warming And El Nino

LONDON, Dec 26 (IPS) - For those who argue that global warming is already changing the world's climate, this year's El Nino weather front is more than enough evidence.

One of the strongest on record, it is responsible for drought in Australia and Papua New Guinea, a delayed monsoon in South East Asia that has led to massive forest fires and choking smog, storms on the Pacific coast of South and Central America, drought in Southern Africa, and threat of floods in Peru and California.

''While there is no definite link between El Ninos and overall climate change, it is worth looking at recent patterns,'' U.S. Vice President Al Gore told the El Nino Community Preparedness Summit in Santa Monica, in the western United States, in November .

The El Ninos have become increasingly severe and frequent through the 1980s and 1990, leading to suggestions that they are being affected by global warming, caused by an increase in heat-trapping greenhouse gases in the upper atmosphere.

Global warming could make the El Nino a permanent feature of the world's weather system, warn some scientists.

El Nino was the name given by Peruvian fishermen to a periodic flow of warm Pacific equatorial waters southward, usually around Christmas time. In the 1960's the phenomenon was linked to the so-called Southern Oscillation, shifts in atmospheric pressure

over the tropical Indo-Pacific region, and El Nino's global reach was established.

El Nino events occur on average every five years, and last up to 18 months. However research now suggests that they are now occurring every three years. In the last decade alone there have been five.

Gore noted that El Nino events had become ''more and more commonplace'' and that global temperatures had risen along with them. ''I hope they don't become more commonplace, but that's what the pattern appears to indicate,'' he said.

Russ Schnell, a scientist doing atmospheric research at Mauna Loa Observatory in Hawaii says: ''It appears that we have a very good case for suggesting that the El Ninos are going to become more frequent, and they're going to become more intense and in a few years, or a decade or so, we'll go into a permanent El Nino.''

He suggests that instead of having cool water periods between El Ninos for a year or two, ''we'll have El Nino upon El Nino, and that will become the norm. And you'll have an El Nino, that instead of lasting 18 months, lasts 18 years.''

While not necessarily endorsing this view, other scientists believe there may be a two-way cause and effect link between global warming and El Ninos.

Kevin Trenberth of the National Centre for Atmospheric Research (NCAR) in Boulder in the western United States, argues that El Nino, not global warming, may be the direct cause of some temperature increases in the Northern Hemisphere winter.

The warming there is due to El Nino-caused changes in jet stream patterns, rather than any increase in temperatures due to greenhouse gases, he says. ''A lot of warming in North America and Eurasia is due to changes in large-scale atmospheric circulation . It's not global warming directly.''

However, Trenberth agrees that global warming could be operating ''behind the scenes''. For instance, the unusual warming in the tropical Pacific and the series of closely spaced El Ninos during the 1990s may reflect some global warming. ''You have to as k yourself. Why is El Nino changing that way?

A direct greenhouse effect would change temperatures locally, but it would also change atmospheric circulation.'' So global warming could be driving El Nino, which in turn could be causing rising temperatures.

Other scientists disagree. El Nino is caused by a decrease in the trade winds that blow from east to west across the Pacific from Peru to Indonesia. To explain El Nino by global warming, it would be necessary to show that global warming caused these trad e winds to stop, says William Nierenberg at the Scripps Institution of Oceanography, and there is no evidence for this.

Moreover, global warming is by definition, global, and it is ''useless'' to try and draw reliable conclusions about its regional effects, such as waters warming in one area of the Pacific Ocean, he says.

There have even been suggestions that ocean circulation changes similar to El Nino could delay global warming in some areas.

Earlier this year, following a statistical analysis of global sea-surface temperatures Mark Cane and colleagues at the Lamont- Doherty Earth Observatory in Palisades, New York, presented evidence that the eastern tropical Pacific has cooled during the pas t century.

They suggest that an overall warming of the atmosphere, such as that caused by an increase in greenhouse gases, could create in the eastern tropical Pacific a natural cooling that will dominate for several decades.

In other words, global warming from increased greenhouse gas concentrations would cause uneven warming in the Pacific, with the western tropical Pacific warming more than easterly waters and this would strengthen the trade winds, bringing more cold water to the surface and increasing the cooling of eastern surface waters.

According to Cane's colleagues, Richard Seager and Amy Clement, the overall effects would be similar to those caused by the so- called 'La Nina', the El Nino in reverse or the 'cool phase' of the El Nino/Southern Oscillation that sometimes follows it.

However, scientists critical of the new findings point out that El Nino warm events, rather than cool events, have dominated the climate over the past 20 years. But Cane says the cooling effect would be shown in the average state of climate, not necessar ily in the year-to-year variability.

''We're starting to appreciate the complexity of the response to greenhouse gases,'' says Clement. ''It's becoming obvious that the idea of a global warming everywhere is probably not correct, and is probably not particularly relevant. It's really the re gional climate changes that we're interested in.''

While the scientific debate continues, global warming and El Nino share one thing, says Michael Glantz, who specialises in climate and culture at NCAR. It is not the issue of climate change or the scientific fact but the human risk factor on which the tw o are being judged.

With climate change, particularly among U.S. policymakers, if the threat is not 100 percent proven the risk is worth taking. People respond differently to each phenomenon, he says.

''Everybody wants to know about El Nino; when you identify an uncertainty, there's an effort to reduce it. But in global warming, people point out uncertainties as reasons not to do anything.'' (END/IPS/MOM/RJ/97)