For the first time carbon dioxide levels in the atmosphere rose by more than two parts per million for two years running, from 2000 to 2001, according to figures recorded by a US scientist and published in the British press.

Climate experts said that the figures may be an anamoly but that they raised the alarm that climate change may be happening faster than previously believed and that governments around the world should take notice.

Global warming leads to melting of the ice caps, higher sea levels and erratic weather.

The figures recorded by US scientist Charles Keeling would be discussed Tuesday at the Greenpeace conference attended by Prime Minister Tony Blair's scientific adviser, David King, the Guardian newspaper said.

Between 2001 and 2002 the number of parts per million of carbon dioxide rose from 371.02 to 373.10, an increase of 2.08 over the year, according to figures published in the Guardian and the Independent. Then it rose again in 2003 to 375.64, an annual increase of 2.54.

The data was recorded at the summit of Mauna Loa mountain in Hawaii by Keeling, who has been collecting it since 1958.

Keeling said that up to then rises of over two parts per million had been recorded in only four years -- 1973, 1988, 1994 and 1998 -- and each time it was a year marked by the climatic phenomenon known as El Nino.

"The rise in the annual rate to above two parts per million for two consecutive years is a real phenomenon," Keeling was quoted as saying.

The most disturbing thing for the 74-year-old scientist was that neither of those two years had been marked by El Nino and there was no data to explain the increase.

El Nino is the climate phenomenon that can catastrophically disrupt weather patterns across the Pacific and beyond.

Keeling said one explanation for the rise "could be a weakening of the earth's carbon 'sinks' (oceans and forests), associated with the world warming, as part of a climate change feedback mechanism."

Meanwhile, Friends of the Earth Scotland's chief executive, Duncan McLaren, said it was "worrying" to see such increases over two years.

"The world can only hope that these figures are an anomaly and not a real trend.

"However, instead of just keeping fingers crossed these findings should send an urgent reminder to governments everywhere of the urgent need to tackle the growing threat of climate change," McLaren said.

Other experts also warned against jumping to conclusions.

King, the main government expert, told BBC News that the two parts per million rise two years running is "likely to be an anomaly, which would not be unprecedented, and not the start of a trend, unless it is proved otherwise".

Peter Cox, who heads the carbon cycle group at Britain's Hadley Centre for Climate Prediction and Research, also told the BBC it was possible to read too much into the figures.

He said that the increase in carbon dioxide was not uniform across the globe and suspected something unusual had happened in the Northern Hemisphere.

He suggested Europe's very hot summer last year and a larger than usual number of forest fires could have killed off vegetation and increased carbon releases from the soil.

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