Loss of Arctic sea ice is changing northern hemisphere ocean currents and atmospheric circulation patterns. A massive influx of warm water as much as 9° F above normal has flowed up the west coasts of both Greenland and Norway towards the Arctic ocean causing a new northern hemisphere weather pattern called the warm Arctic cold continents pattern to develop.
Temperature anomaly in ° C at 100 meters depth in far northern waters.

Warm water has flowed into the Arctic and the northern seas as Arctic sea ice volumes have collapsed, allowing for a faster Arctic currents. Those enhanced currents have flushed Arctic sea ice and Greenland glacial melt water down the east coast of Greenland and enhanced the flow of warm Atlantic ocean water up the west coasts of Greenland and northern Europe.
Much above normal sea surface temperatures surround southern Greenland.

The shift from last year's El Nino conditions to this year's La Nina has not stopped the return of the warm Arctic cold continents pattern which happened for only the third time in 160 years last winter. This pattern is associated negative North Atlantic oscillation index which happens when there is a week pressure gradient between Iceland and the Azores island. Last winter high pressure sat where the Iceland low usually is located while low pressure areas swung far south where the Azores high is usually located. Greenland was exceptionally warm while Europe and the eastern United States were exceptionally cold and snowy.
The winter of 2009 - 2010 had the most extreme negative NAO since record keeping began in 1950. The NAO index was negative 1.67, beating the previous record of negative 1.47 set in the winter of 1962 - 1963. The record negative NAO was responsible for unusual cold weather and snows over Eastern North America and Europe, and resulted in an upside-down winter: coldest in 25 years in the U.S., and warmest on record in Canada, with snow needing to be trucked in for the Winter Olympics in Vancouver. This "Warm Arctic-Cold Continents pattern" had occurred previously only three times in the past 160 years. If a strong negative NAO establishes itself this winter, we could have a winter like 1995 - 1996, which featured a weak La Niña and a strongly negative NAO. That winter featured many cold air outbreaks across the Eastern U.S., resulting in fifteen major cities setting new all-time seasonal snowfall total, including 75.6" at New York City's Central Park. Unfortunately, the NAO is not predictable more than about two weeks in advance.

Why is the strange pattern happening again this year? Heat transferred from the warm oceans to the Arctic atmosphere has weakened the temperature difference between the tropics and the poles, weakening the jet stream. However, there is a very strong temperature gradient between the much warmer than normal water in the Labrador sea and the cold north American Arctic. The warm waters enhance the south to north jet stream winds along the east coast of north America.
A pattern called a blocking high tends to develop over Greenland as warm air rises up from the ocean into the atmosphere above Greenland. This blocking high pattern has been affecting our weather recently, bringing snow to England, cold to Europe and the north eastern United States.
Blocking high over Greenland November 29, 2010 at 300mb level

Delayed English train arrives Dec. 2, 2010 credit: Gareth Fuller, Guardian
The blocking high will continue to bring cold weather this weekend and for the coming week ahead according to forecast models.

This could be the beginning of a long term change in the winter weather patterns for the northern hemisphere. The warm Arctic cold continents pattern may happen much more frequently.
