Poor El Nino! It is accused in recent times of causing everything unusual that happens to our weather, writes Brendan McWilliams. It has been indicted for floods in both America and Europe, for droughts in the Antipodes, typhoons in the Pacific, and even the exorbitant coffee price in Brazil. Most recently, El Nino stands accused of being the emi- nence grise behind the widespread "smog" that covers a large swathe of South East Asia. But this time, even though the trail of detection may be somewhat tortuous, the evidence, prima facie, is convincing.
It was a London physician with the unlikely name of Harold A. Des Veaux who coined the word "smog" in 1905 to denote an obscuring mixture of smoke and fog. Smoke, itself, of course, reduces visibility directly, and much of the problem in Indonesia and nearby is simply that: a thick, dry, haze of smoke. Over much of the region, the term "smog" is inappropriate.
But the naturally humid climate plays its part. Even when there is an abundance of water vapour, it is reluctant to condense in a clean atmosphere, but it does so readily if there are small particles, or nuclei, on which droplets can form. Smoke particles are ideal for this purpose; they provide conditions so favourable that it is almost as if the moisture cannot wait to condense, doing so when relative humidity may be only 90 per cent, and obscuring visibility much more.
But why, on this occasion, do we blame El Nino? El Nino, as nearly everybody knows by now, is a periodic warming of surface waters of parts of the tropical Pacific. It occurs at irregular intervals of about three to seven years, but last autumn oceanographers were surprised to find that sea surface temperatures off the western coast of South America were two or three degrees above normal. Another El Nino was on the way, only 18 months after the last episode had ended.
The El Nino phenomenon has predictable effects on weather near the tropics. It brings storms and torrential rains to the arid coastal regions of Peru and Ecuador; more significantly in the present context, Indonesia and other parts of South East Asia that normally enjoy an abundance of tropical rainfall, experience prolonged droughts. This has been happening in recent months, and has led, apparently, to normally controllable forest fires running amok through a parched landscape.