The annual survey of the World Meteorological Organisation says that 1997 was the hottest year on record. They put the blame mainly on El Nino, rather than global warming.

According to a report from the United Nations weather agency this week, last year was the warmest since records were first kept in 1860. The average temperature at monitoring stations on land and sea was 0.44 degrees Celsius above the average for the period from 1961-1990. The previous highest figure of 0.38 above the average was recorded in 1995.

There are essentially three things we can do when we hear such news: say "how interesting", then get back to whatever we were doing; wring our hands in horror and blame global warming; nod our heads as if we had seen it coming and blame El Nino. Options two and three may also be combined by blaming El Nino on global warming.

"Everybody blames El Nino for everything," said Eirah Gorre-Dale, a spokesman for the World Meteorological Organisation, "but that is not always right." As the report made clear, however, a good deal can be attributed to El Nino. Developing rapidly during April, it had by May pushed sea surface temperatures in the central and eastern Pacific to 28C - five degrees higher than normal. The resulting warmer air led to a dramatic reduction in rainfall in the area and sent hot air downwards across the Indian Ocean. That led to drought in Indonesia, which fuelled the forest and brush fires throughout south-east Asia and bush fires in Australia. Drought also struck the northern part of South America, as well as the Caribbean and Central America.

Meanwhile, the heavy rains that should have fallen in those areas was diverted to cause major floods in central and southern parts of South America and central and southern Africa. More than 1,200 people died in the worst floods for 30 years in Somalia, and Kenya continues to suffer from floods disrupting transport and economic life.

On the other hand, 1997 also saw major flooding in the Red River basin in the US, the "flood of the century" in the Czech Republic and Poland, torrential rain in southern China and an unusually hot, dry summer in north China and North Korea. The WMO acquits El Nino of direct involvement in all of those, and also, perhaps more surprisingly, of responsibility for the ice storm that has crippled Canada.

But where does global warming fit into the picture? First, the WMO warns most sensibly against inferring too much from any global average temperature. Such an average, taking into account widely differing figures from freezing mountain tops to the steamy tropics, makes no scientific sense, according to one WMO expert. Despite that, however, and despite the fact that the Middle East, northern India, large parts of Australia and two-thirds of North America were colder than average last year, the evidence confirms that the world is getting warmer.

The ocean currents that determine the strength of El Nino, however, are so poorly understood and so slow in operation that we may need another hundred years' data to establish a possible connection between El Nino and global warming.

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