Last year tied with 2010 as the hottest on record, in a new sign of long-term global warming stoked by human activities, according to British data on Monday that back up U.S. findings of record-breaking heat in 2014.
The worldwide data, compiled by the Met Office and the University of East Anglia from records stretching back to 1850, showed average surface temperatures last year were 0.56°C (1.0°F) above the long-term average of 1961-90.
"This ranks 2014 as the joint warmest year in the record, tied with 2010, but the uncertainty ranges mean it's not possible to definitively say which of several recent years was the warmest," a joint statement said.
With 2014, all of the 10 warmest years on record have been this century, with the exception of 1998.
Given the statistical ranges, the data echoed U.S. findings. On January 16, the U.S. space agency NASA and the National Oceanographic and Atmospheric Administration said last year was the warmest on record, just ahead of 2010.
The British team said the findings showed "several data sets in broad agreement". Discrepancies occur because they use different ways to determine temperatures in places with few thermometers, such as the Arctic.
The statement linked a long-term trend of rising temperatures in recent decades to human emissions of greenhouse gases, mainly from burning fossil fuels.
China, the United States and India are the top emitters. Almost 200 governments have agreed to limit global warming to 2°C above pre-industrial times, and temperatures have already risen by about 0.9°C. Governments will meet in Paris in December to work out a deal.
Sceptics who doubt that humans influence the climate often point to what U.N. studies have called a hiatus in warming in recent years, perhaps linked to natural variations in the sun's output or factors such as sun-dimming ash from volcanoes.
"To say that warming has stopped is not accurate," Professor Tim Osborn of the University of East Anglia told Reuters. But he said the pace of warming had been faster in the 1980s and 1990s.
Thomas Stocker, a professor at the University of Bern who co-chaired a 2013 U.N. report about climate change, said the recent run of warm years meant "the possibility is quite there that this hiatus is over".
Still, he told Reuters that climate trends had to be judged over decades, not by individual years.
