Image caption Despite a record hot year in the US, the rest of the world did not follow

US scientists say that 2012 was among the 10 warmest years the world has experienced since 1880.

Nasa researchers said it was the ninth warmest year while experts from another American agency said it was the 10th.

Both teams said that temperatures would have been higher if it had not been for the La Nina weather pattern that brought cooling to some regions.

They were equally certain carbon dioxide had been the principal driver of the rise over the past 50 years.

The National Oceanic and Atmospheric Administration (Noaa) said that their analysis of temperature data from a global network of weather stations indicated that the average temperature for 2012 was 0.57C above the 20th Century average.

The agency stated that all 12 years of the 21st Century rank among the 14 warmest in the 133-year period of record keeping.

"This past year, unlike the US they were not a record globally but they certainly were warm," said Thomas Karl, director of Noaa's National Climatic Data Centre.

"In fact, it marks a persistent above average - every year has been above average since 1976."

Using the same data but carrying out a slightly different analysis, Nasa said it was the 9th warmest year with temperatures 0.6C warmer than the mid 20th century baseline.

Dr James Hansen, from Nasa's Goddard Institute for Space Studies, acknowledged that even in a period of global warming some seasons will be cooler than the long term average.

"The perceptive person should notice that the frequency of unusually warm extremes is increasing. It is the extremes that have the most impact on people and other life on the planet," he said.

According to both groups of researchers, most areas of the world had higher than average temperatures in 2012 while the Arctic experienced a record breaking ice melt.