Global-warming anomaly `solved'

SCIENTISTS HAVE found a possible explanation for contradictory reports about global warming, which some experts have used to cast doubt over whether pollution is responsible.

Satellite measurements of the lower atmosphere have consistently found it has cooled over the past two decades, contradicting temperature measurements on the ground, which have shown a consistent rise.

Scientists have looked again at the atmospheric temperature measurements and found that the discrepancy can be explained by a gradual fall in the altitude of the temperature-measuring satellites as they orbit the Earth.

When the scientists compensated for the ``falling satellite'' effect they found that temperatures of the lower atmosphere have actually risen, bringing them more in line with the increase in average surface temperatures.

A scientific consensus has emerged that global warming is real, with pollution to blame.

Some scientists have nevertheless exploited anomalies in the global temperature readings to cast doubt on the idea that man-made emissions of greenhouse gases, such as carbon dioxide, are responsible.

However, Frank Wentz and Matthias Schabel, who work for a Californian consultancy, Remote Sensing Systems, report in the journal Nature that the atmospheric cooling effect of 0.05C per decade, as detected by satellite between 1979 and 1995, is more likely to be a real rise of 0.07C per decade.

This brings the changes in the temperature of the lower atmosphere more into line with the reported increase in the average temperature of the Earth's surface, which is accepted to be 0.13C per decade.

``The difficulty in reconciling the information from these different sources has sparked a debate in the climate community about possible instrumental problems and the existence of global warming,'' Mr Wentz and Mr Schabel write.