TALLINN - Northern Europeans have been poised to celebrate the passage to the new year in a way that is out of the ordinary for them: with an ice-free Baltic Sea.

"It's quite unusual that we welcome the new year with no ice in the Baltic Sea," Tarmo Kouts, senior researcher at the Estonian Marine Institute, told AFP on Friday.

Temperatures in Estonian coastal waters are warmer by one degree Celsius (around three degrees Fahrenheit) than at the end of last year, Kouts said.

"The temperature of 1C in the Bay of Parnu means conditions are ready for ice formation, if only we had at least a week of sub-zero temperatures," Kouts said.

"But the forecast shows mild weather continuing into the New Year."

Still, he assured, the sea could freeze this winter.

"It would take up to 10 days of freezing temperatures and we would see ice forming in the coastal areas," Kouts said.

"It's too early to rule out ice altogether for this winter."

Winters with little ice in the Baltic Sea are happening more frequently, and often it is only the Bay of Parnu in Estonia and the Gulf of Bothnia near Finland and Sweden that develop a layer of ice.

The warm winters of recent years stem from climatic change, but do not yet indicate an irreversible trend, Kouts said.

According to Kouts, the last time the region had particularly warm winters was in the late 1980s and early 1990s, when four winters in a row saw above-average temperatures.

To find a similar series of warm winters before that, you would have to go back several hundred years, he said.

Meanwhile, the winter of 2002-2003 was significantly colder than average, Kouts said.