Warm year shows evidence of air pollution air

The Eighties and early Nineties have been the planet's hottest years since about 1860. Nicholas Schoon reports

This year will be the Earth's third or fourth warmest since global temperature records began more than a century ago.

The finding, by British scientists, adds weight to the theory that pollution has already made a detectable difference to climate. Last year was also a very warm year in Britain.

The Meteorological Office is forecasting that it will turn out to be among the 10 warmest years in the central England temperature records, which stretch back to 1659.

The Eighties and the first five years of the 1990s have been the planet's hottest years since about 1860 when reliable temperature records began to be kept for most of the planet's land and sea surfaces.

The warmest year was 1990; almost 0.4 degrees Centigrade above the average for 1951 to 1980, according to scientists at the Met Office's Hadley Centre for Climate Prediction and Research and the University of East Anglia.

They analyse millions of temperature measurements from more than 1,000 weather stations on land and from ships at sea to produce a global average monthly temperature. The next warmest year was 1991.

And, with 11 months data already analysed for 1994, the scientists believe this year will either be third equal with 1988 or just behind in fourth place - at 0.31C above the 1951 to 1980

average of just under 15C. Of the 10 warmest years in the 135-year global record, all but one (1944) have occurred since 1980.

"Nobody really denies that there has been a warming in the 1980s and 1990s,'' said Dr David Parker, of the Hadley Centre. "The question is whether it's part of the natural variability of the climate system or man-made global warming."

A build-up of carbon dioxide and other man-made `greenhouse gases', such as methane and nitrous oxide, is expected to raise temperatures across most of the globe.

These pollutants, mostly produced by the burning of fossil fuels and tropical forests, act as a heat trap. Their steady accumulation in the atmosphere has been measured over the past few decades.

But there is much debate among scientists over the rapidity and extent of this warming, and how it will alter rainfall, wind patterns and regional climates.

Its impact in the next century could range from the minor to the colossal, killing or displacing hundreds of millions of people through famines, destructive storms and sea level rise.

The early 1990s would have been much hotter years still but for the Mount Pinatubo eruption in the Philippines in 1991. This injected huge quantities of haze into the upper atmosphere, which spread around the world and blocked out some of the Sun's warmth.

On the other hand, some of the warming of the past few years has been due to the El Nino effect. This is a climate phenomenon which occurs every three to ten years and usually lasts about two years, although the latest one has been going on for longer than usual.

El Nino involves drastic changes in winds, temperature and the up welling of cold water from the deep Pacific in tropical latitudes off the South American coast. It has a strong influence on weather thousands of miles away, from North America to Australia where it has caused a prolonged drought.

Closer to home, the Met Office predicts that 1994 will turn out to be the sixth warmest year this century after a freakishly mild November and the eighth warmest since 1659. The office has a temperature record for the central England area stretching backmore than three centuries.

In the 17th and early 18th centuries very few people were using the recently invented thermometers, and there was no universal Centigrade or Fahrenheit scale.

Nevertheless, it has proved possible to construct a temperature record, based largely on diaries kept by the gentry, land agents and clergymen.

They recorded the dates of the harvest, extremes of weather, days of frost and the length of time that snow lay on the ground.

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