The global temperature has risen to a record for a 12-month period, according to Nasa.

The analysis undermines the case made by climate sceptics, who have used the slight cooling trend in recent years to argue that man-made emissions are not causing global warming.

The average surface temperature for the year to the end of April was about 0.65 of a degree Celsius (1.17 degree Fahrenheit) higher than the 1951 to 1980 average, according to Nasa’s Goddard Institute for Space Studies. That makes it a fraction warmer than the previous peak detected by Nasa in 2005.

The Nasa study said: “We conclude that there has been no reduction in the global warming trend of 0.15-0.20°C/decade that began in the late 1970s.”

The Met Office said its own analysis of temperature records suggested that the global temperature remained just below the 12-month record achieved in 1998. However, Vicky Pope, head of climate advice, said it was possible that Nasa was correct because the Met Office had underestimated recent warming detected in the Arctic.

There are very few weather stations in the Arctic and the Met Office, unlike Nasa, does not extrapolate where there are no actual temperature readings.

Ms Pope said that other information, including that from satellites, indicated that the Arctic was warming more rapidly than other parts of the world. She said this evidence supported Nasa’s results but neither it nor the Met Office had taken it into account in their assessments of global temperatures.

“Nasa may be correct that we have just seen a new 12-month record in global average temperature. The Met Office continues to predict that 2010 is more likely than not to be the warmest calendar year on record, beating the 1998 record.”

She added that Met Office analysis showed that the four months to the end of April were probably the third warmest for that time of year.

Nasa and the Met Office both interpret information from 6,300 monitoring stations around the world and their results are used by the United Nations Intergovernmental Panel on Climate Change to compile its advice to governments.