2004 the 4th hottest year

Greenhouse gases and to a lesser extent the El Nino current in the Pacific Ocean contributed to making 2004 the fourth warmest year on Earth since temperature measurements began worldwide at the end of the 19th century, Nasa scientists said.

"There has been a strong warming trend over the past 30 years, a trend that has been shown to be due primarily to increasing greenhouse gases in the atmosphere," said James Hansen, a climatologist at Nasa's Goddard Institute for Space Studies, outside Washington.

The warmest years on record were, in descending order, 1998, 2002 and 2003, the National Aeronautics and Space administration said on its website.

In 2004, the average global temperature was 14� degrees Celsius, or 0.48� Celsius warmer than any year between 1951 and 1980, Hansen said.

The regions with the highest rise in average temperatures last year were Alaska, the Caspian Sea region and the Antarctic Peninsula.

Solar heat trapped by the accumulation of greenhouse gases - especially carbon dioxide spewed out by cars and industries - and the warming effect of the El Nino current could make 2005 approach the record warmth of 1998, Nasa said.

The scientists said the warming trend is already significant enough to permanently make the seasons warmer.

Nasa determines planetary cooling or warming by measuring the temperature at numerous spots around the world, both at ground level and over the oceans from orbiting satellites.

The issue of global warming is controversial, especially in the United States, whose administration has opposed mandatory curbs on the emission of greenhouse gases like carbon dioxide, which researchers agree is one of the main causes of global warming.