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I . What's Happening to Global Climate?

Is El Nino Now a Man-made

Phenomenon?

- B Y ALAIN-CLAUDE GALTIE -

Instead of appearing every four to seven years. El Nino has now been appearing consecutively for a number of years and in a stronger form than ever before in human history - severely disrupting agriculture and economies across the planet. Could it be that global warming and the destruction of tropical rainforests are responsible for the change?

We have been warned; we are now beginning to experi­ ence the convulsions of a climate that is changing fast. And nothing could be more indicative of that change than the 1997/98 El Nino, which in the UK Met Office's own words was "the most extreme on record". El Nino, the 'Christchild' - so-called because it tends to show its face around Christ­ mas - is a natural phenomenon, something that the world has experienced since time immemorial. That makes it all too easy to blame the strength and violence of the latest El Nino on a phe­ nomenon which has nothing to do with us. El Nino has become the scapegoat for practically all the appalling weather experienced over the past year. That is a dangerous misconception: it lets us off the hook when, because of global warming, and particularly because of our destruction of the environment in the Tropics, we are setting the scene for catastrophic changes to the basic nature of El Ninos. They are becoming more violent and they are lasting longer. Particularly worrying too, for all the growing sophistica­ tion of our climate models, is that we were unprepared for this El Nino when it came. The best our models could do was to indicate that the year of the next El Nino would be 1998/99 and not 1997/98. I f we can be as wrong as that, then we clearly have to question the basis of our understanding of what goes on in gener­ ating such a major switch in the world's largest ocean.1

The impac t of th e 1997/1998 El Nino The latest El Nino involved massive releases of energy from the Pacific Ocean. The 1997/98 El Nino took hold in the late summer and autumn of 1997. The first signs were a sudden warming of the tropical waters off the coast of Peru by as much as 6°C, combined with violent downpours and landslides in what is one of the driest deserts in the world — the Atacama. It also spawned Hurricane Pauline that hit the south-west of Mexico early in September, destroying roads and bridges as well as demolishing entire coffee plantations in the mountains of western Oaxaca. Across the other side of the Pacific, where giant cumulo-nimbus clouds normally bank up as a prelude to the monsoon rains, the skies remained clear and open to the scorching sun. The monsoon rains barely arrived and South-east Asia was left with withering heat and dev­ astating drought. Papua New Guinea had to declare a state of emergency as crops failed; starvation was only staved off because of airlifts of foods and medicines from Australia and New Zealand. The lack of rain had dire consequences right across the globe and fires continued to rage over a 200-square-kilometre region in Indonesia's East Kalimantan, months after they were first lit by forest clearers. The fires burrowed down into the mas­ sive peat bogs associated with Indonesian forests, releasing into

the atmosphere carbon that had been stored over the past 10,000 years.

Conditions in Brazil's northern Amazon were just as bad. There, fires destroyed over 6,000 square kilometres. And late in 1998, after months of burning, forest fires in the Khabarovsk dis­ trict of Russia on the Pacific coast had already wiped out two mil­ lion hectares. That's an awful lot of carbon dioxide sent pluming into the air and it can be no coincidence that the amount of carbon dioxide accumulating in the atmosphere in 1998, as measured at Mauna Loa, Hawaii, jumped upwards by one-seventh compared with the previous peak.2 Just the fires in the world's tropical regions released as much carbon dioxide as is vented from all of Western Europe's agriculture and industry in one year. And not one of those fires can be called 'natural': they were all lit by humans, mainly in their attempt to convert tropical rainforest into plantation crops and cattle ranches.

Fires, too, and desperate drought were the order of the day dur­ ing the year of the 1982/83 El Nino. Thousands died of starvation

The general belief is that the Southern Pacific Ocean acts like a capacitor, mopping up energy in the form of heat, until a point is reached when the system overloads and dumps the energy in one dramatic moment. Although the mechanism is not clear, the extra heat going into the oceans because of global warming appears to have tipped the balance to more frequent El Nihos as well as more severe ones. in the Sahel countries of Africa and at least 36,000 square kilome­ tres were destroyed by fire in Borneo. Meanwhile, rainfall over the Amazon went down by 30 per cent. That implies an enormous energy change in the climate system — close to 160 terawatts — and equivalent to some twelve times the total amount of energy now used by humans across the globe.

It seems that El Nino hits hardest where we have already begun to degrade the environment. Indeed, we can see with dramatic effect what tropical storms can do to the environment when it has been degraded and destroyed. The horrendous damage that hurri­ cane 'Mitch' caused in Honduras and Nicaragua was largely the result of deforestation, which left soils exposed and vulnerable to sheet erosion and massive landslides that buried whole villages (see picture). Having lost 34 per cent of its pine and deciduous for-

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The Ecologist, Vol. 29, No 2, March/April 1999 IS E L NIN O NOW A MAN-MAD E PHENOMENON ?

The devastating impact of Hurricane Mitch in Honduras on El Nino blamed

est through logging between 1964 and 1990, Honduras is still con­ tinuing to destroy its native upland forests at the rate of 80,000 hectares each year. The situation is even worse in Nicaragua: there, 150,000 hectares of forest are destroyed each year as a result of commercial timber extraction, the advancing agricultural fron­ tier, slash-and-burn farming and human-lit forest fires. The coun­ try has lost nearly 60 per cent of its forest cover in the last 50 years.

What could be a more obvious prelude to disaster? And were El Nino to become the norm that would play havoc with our systems of agriculture. We would experience torrents of unseasonal rain where before the weather had been dry and catastrophic drought where before we experienced summer monsoons.

El Nino and La Nina i n normal time s Until twenty years ago El Ninos would occur every four to seven years, last for one year, and give way to the opposing climate regime, which as a consequence has been dubbed La Nina. La Ninas therefore follow hard on the heel of El Ninos, but where El Nino brings drought, La Nina brings rain and vice versa. As far as the Pacific Ocean goes, El Nino goes hand in hand with an expanding region of warm waters, while La Nina presents the 'cool' side, with strong upwellings in tropical waters of cold cur­ rents from Antarctica. The more usual climate pattern occurs in the intervals between such oscillations. 'Normal' therefore means monsoon rains over South-east Asia, a rain-drenched Amazon, rains over arid Sahelia in Africa, some dousings of rain over Aus­ tralia and extremes of high pressure over the west coast of South America, south of the Equator. La Nina, as well as a 'normal' Pacific Ocean, bring rich fish harvests to the Peruvian fishermen and account for the mountains of 'guano' — bird manure — that have accumulated because of the gathering of millions of seabirds. In such years, the Trade Winds blow strong and drive the waters of the Pacific Ocean from East to West, so that by the time they have piled up against South-east Asia they have burdened

themselves with massive amounts of water vapour that are released as the air rises up over the opposing air currents pushing up from the Indian Ocean. The movement of water across the Pacific allows the cold waters of the Humboldt Current to surface along the South American coast south of the Equator. Loaded with vital nutrients, the Humboldt Current hosts a profusion of life.

When the normal regime gives way to El Nino, then the Hum­ boldt Current is held down by a thick cap of warm waters. With­ out the nutrients, the rich biological cycle is broken. Without the phytoplankton, the populations of the minute plankton-feeding zooplankton crash, and so on, to the fish and then to the seabirds. The difference is momentous. In a good year, such as in 1970, Peruvian fishermen took 12 million tons of anchovies from the sea. Three years later, an El Nino year, the catch plummeted to less than two million tons.

Causes of violen t El Ninos - global warming? The New Zealand climatologist Ken Trenberth, now at the Nation­ al Center for Atmospheric Research in the United States, was the first to pinpoint the four-to seven-year cycle of El Ninos. He there­ fore sees the sharp change in pattern of El Ninos since the mid-

The Ecologist, Vol. 29, No 2, March/April 1999

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