Winter in the Northern Hemisphere this year has been the warmest since records began more than 125 years ago, a US government agency says.
A lack of snow in Europe has affected business at ski resorts
The combined land and ocean surface temperature from December to February was 0.72C (1.3F) above average.
The National Oceanic and Atmospheric Administration said El Nino, a seasonal warming of parts of the Pacific Ocean, had also contributed to the warmth.
But it did not see the high temperature as evidence of man-made global warming.
The Noaa said that temperatures were continuing to rise by a fifth of a degree every decade. The 10 warmest years on record have occurred since 1995.
Weather experts predict that 2007 could be the hottest year on record.
"Contributing factors were the long-term trend toward warmer temperatures as well as a moderate El Nino in the Pacific," said Jay Lawrimore of Noaa's National Climatic Data Center.
He added: "We don't say this winter is evidence of the influence of greenhouse gases."
However, Mr Lawrimore said the research was part of the Intergovernmental Panel on Climate Change (IPCC) process, which released a report last month that found global climate change "very likely" has a human cause.
"We know as a part of that, the conclusions have been reached and the warming trend is due in part to rises in greenhouse gas emissions," he said.
The IPCC panel concluded that it was at least 90% certain that human emissions of greenhouse gases rather than natural variations are warming the planet's surface.
They projected that temperatures would probably rise by between 1.8C and 4C by the end of the century, though increases as small as 1.1C (2F) or as large as 6.4C (11.5F) were possible.