The odds of a "white Christmas" in temperate parts of the northern hemisphere have diminished in the last century due to climate change and will likely decline further by 2100, climate and meteorology experts said.

Even though heavy snow this year will guarantee a white Christmas in many parts of Asia, Europe and North America, an 0.7-degree C rise in world temperatures since 1900 and projected bigger rises by 2100 suggest an inexorable trend.

"The probability of snow on the ground at Christmas is already lower than it was even 50 years ago but it will become an even greater rarity many places by the latter half of the century," said Friedrich-Wilhelm Gerstengarber, climate researcher at the Potsdam Institute for Climate Impact Research.

In the northern German city of Berlin, for instance, the chances of snow on the ground on Dec 24, 25 and 26 have fallen from 20 percent a century ago to approximately 15 percent in 2008, he said. By 2100 the odds will be less than 5 percent.

Berlin last had snow on the ground at Christmas in 2001, and even though the German capital is due a festive snowfall, from a statistical point of view, meteorologists say it will not be white in 2008 either.

In cities with more maritime climates, such as London, and mild continental climates like Paris, snow on Christmas is even now fairly rare and will only be a freak occurrence within 100 years, he said. No snow is expected in either city this year.

"The yearning for snow at Christmas seems to grow stronger the rarer it becomes," Gerstengarber said, noting cities at low altitudes such as Berlin (30 m above sea level) will probably almost never see snow surviving on the ground by 2100.

Betting on the fabled "white Christmas" is a pastime in some countries, like Britain, and oddsmakers will increasingly have to factor in global warming's impact, climate researchers said.