"We are now experiencing the warmest period (for this season) in the past 1,300 years," said Reinhard Boehm, chief climatologist at Austria's Central Institute for Meteorology and Geo-Dynamics in Vienna.

He cited a study by a group of European climatic institutes that reconstructed more than a millennium of weather patterns in a region ranging from France's Rhone Valley in the west to Hungary in the east, and from Germany's Nuremberg area in the north to Italy's Tuscany in the south.

Temperatures generally did not diverge from a naturally frigid winter level except for one thaw between the 10th and 12th centuries, and Alpine glaciers reached their greatest size around 1850, Boehm told Austrian press agency APA.

Industrial pollution originating in the 19th century began to affect climate from the mid 20th, he said. Unfiltered factory smoke and other emissions initially cooled temperatures somewhat as they impeded the sun's rays, he said.

The latter-day warming trend set in about 20 years ago from the cumulative use of fossil fuels giving off clear greenhouse gases such as methane and carbon dioxide, said Boehm.

"This has led to ever higher temperatures since the 1980s and the models indicate that it's going to get even warmer in future," Boehm said.

Many scientists say a single warm winter is most likely part of the natural variations of an unpredictable climate. Still, years of mild temperatures fit predictions of global warming, widely blamed on human use of fossil fuels.

Like many places, Austria had its mildest autumn since records began and many ski resorts have delayed the season's kick-off. Snow cannons sit still on green slopes that would usually be pistes, shrinking the billion-dollar winter business.

Glaciers are receding. Rare December pollen is troubling asthma sufferers as far north as Scandinavia, sales of winter clothing are down and Santa Claus is having to reassure children his sleigh will take off on Christmas Eve, snow or no snow.