2012 was ninth warmest year on record with temperatures significantly above long-term average

Average global surface temperature in 2012 was 0.56C warmer than the average for the period 1951 to 1980

All of the top ten warmest years have occurred since 1998 (Getty Images)

Last year was one of the ten warmest years on record with temperatures significantly above the long-term average according to official assessments by American scientists released tonight.

The average global surface temperature in 2012 was 0.56C warmer than the average for the period 1951 to 1980 and, overall, the year was nominally the ninth warmest on record, although it was barely indistinguishable in rank from several other years, said James Hansen, director of Nasa’s Goddard Institute for Space Studies in New York.

Although global temperatures have been flat for about a decade, all of the top ten warmest years have occurred since 1998 and the “climate dice” are now sufficiently loaded for people to notice that unusually warm seasons are occurring much more frequently than they did a few decades ago, Dr Hansen said.

Temperature extremes that go beyond what is expected occurred in 2010 over a large region of Eastern Europe including Moscow, over Oklahoma, Texas and Northern Mexico in 2011 and in the Rocky Mountains and Great Plains of the US in 2012, Dr Hansen said.

The analysis of global temperatures in 2012 by scientists at Nasa and the US National Oceanic and Atmospheric Administration (NOAA) found that the rate of increase in warming has continued to flatline, although Dr Hansen said that this does not mean that global warming has “stopped” as some climate sceptics have claimed.

“The 5-year running mean of global temperature has been flat for the past decade. It should be noted that the ‘standstill’ temperature is at a much higher level than existed at any year in the prior decade except for the single year 1998, which had the strongest El Nino of the century,” Dr Hansen said.

“We conclude that the background global warming is continuing, consistent with the known planetary energy imbalance, even though it is likely that the slowdown in climate forcing growth rate contributed to the recent apparent standstill in global temperature,” he said.

Nasa said that the level of carbon dioxide in the atmosphere was about 285 parts per million in 1880, the first year in the Goddard Institute’s temperature record. By 1960, the atmospheric carbon dioxide concentration, measured at NOAA's Mauna Loa Observatory, was about 315 parts per million. Today, that measurement exceeds 390 parts per million.

Gavin Schmidt, a climatologist at Goddard, said: “One more year of numbers isn't in itself significant. What matters is this decade is warmer than the last decade, and that decade was warmer than the decade before. The planet is warming. The reason it's warming is because we are pumping increasing amounts of carbon dioxide into the atmosphere.“