Global warming, Gulf Stream and Scandinavian climate

During the first years of climate debate croakers predicted a new ice age in Scandinavia as a result of global warming and reduced Arctic sea ice. The “pump” of the Gulf Stream is the so-called deep-water formation when warm surface water is cooled and ice is formed. After ice formation the cold water with a higher salt content will sink as it has a higher density than the incoming warmer water. They predicted that less ice would reduce the power of the pump, thus leading to colder weather. It was however above my capability to understand how reduced sea ice could cause an ice age in Scandinavia without this ice cover in turn would lead to more sea ice in the Arctic. How could the result of warming be cooling?

Now this strange vision is abandoned and the forecast is a steady worldwide temperature increase, especially near the poles. What is evident for me, living in the northern part of Sweden, is that especially the autumns are warmer and longer than before. Earlier this winter it was draught and fires in Western Norway and just now, in February, we have an unusually long period of mild weather in Northern Sweden while England suffers from floods.

Generally Scandinavia has a higher annual mean temperature than other places at the same latitude. The cause of this is the warm water brought far north by the Gulf Stream. The croakers mentioned above predicted that climate change would reduce the flow of the Gulf Stream resulting in colder weather in Scandinavia. Now, when we see the opposite, how can this warmer weather be explained?

A generally warmer climate will of course lead to higher temperatures, but for us in the north it is the Gulf Stream that determines the climate. The meteorologists talk about what is going on in the atmosphere when they make their weather forecasts while the climate in general has a clear correlation with conditions at the surface, whether it is land, sea, flat areas or mountains.

Therefore I find it likely that the changes we have seen up here during the last years not only has to do with general changes in atmospheric conditions, but are directly coupled to changes in our main source of energy – the Gulf Stream. The global ocean currents form a complex system. For us in the north, the Gulf Stream is the most important part of this system.

The theory presented below was first put forward to Christian Bigler of Umeå University during a lecture in Skellefteå in the autumn of 2007. He did not dismiss my hypothesis, but, at that time, the measurement support was not sufficient to decide whether it was correct or not. Since then I have tried from time to time to get it confirmed or dismissed, but without any response. It is my hope that describing it here in my blog will give a better response. My reasoning is based upon the knowledge I, a chemical engineer, have about heat transfer.

When the warm water of the Gulf Stream flows under the ice of the Arctic Sea, it is cooled on the underside of the ice, which temperature is always 0 ºC. This provides a steady, but moderate cooling largely independent of the conditions in the air above the ice, whether it is summer or winter. In ice-free areas however the heat transfer is directly with the air.

During the Arctic summer, this means little or no cooling (possibly even heating) of the surface water in ice-free areas.

However, during Arctic winter, the cooling of the surface water is stronger in open sea than in ice-covered areas. The air is very cold (far below 0 ºC) and there are often turbulent conditions because of strong winds. This means a more powerful cooling autumn and winter of open areas than if they were covered with ice!

In a situation where less and less Arctic Sea areas are covered with ice, my conclusion is that the Gulf Stream will be slowed down during spring and summer, while the velocity will increase during autumn and winter, giving bigger seasonal variations in the Gulf Stream than before. This will not in itself lead to changing average annual temperatures in Scandinavia, but to a shift in seasons where falls gets warmer and longer while springs/early summers are colder than before. These are trends that I personally think I’ve seen in recent years.

According to NSIDC the actual (14 February) Arctic ice surface seems to be the lowest ever. Especially remarkable are the big areas of open sea north of Svalbard and in the Barents Sea between Svalbard and Novaya Zemlya. Is there a possibility that the system now is self-supporting, that means that the Gulf Stream now is especially strong and the amounts of warm water it brings up north keep larger areas open, thus increasing the cold water formation, which in its turn increases the Gulf Stream even more?

Then, if more warm water is coming up with the Gulf Stream this winter, the cold water formed has to go back somewhere. Could this cause the cold weather North America has had this season?

At the opposite part of the World, in Antarctica, I understand there have also been changes in the ocean currents. If more cold water is brought to the south coast of Australia, this should lead to an increased risk of draughts and thus bes devastating for the country.

Generally, how much is known about the relationship between global warming and changes in ocean currents? Are the theoretical considerations supported by direct measurements of ocean currents.

One Response to "Global warming, Gulf Stream and Scandinavian climate"

  1. After having published the post above I took contacts with some relevant scientists. Professor Kjell Arild Orvik at the University of Bergen has been very helpful in terms of supplying information based on Gulf Stream measurements, mainly from the socalled Svinøy section. His measurements confirm that there are seasonal variations in the flow of the Gulf Stream, but contradict my predictions that those seasonal variations are increasing. The strongest seasonal variations were in fact in the period 1997-2001 with an absolut maximum in 2004/2005.
    Concerning other parameters there are data showing a slight decrease in the mean flow of the stream during 1995-2005 while the water temperature during the same period was increasing. The net result was that the heat flux brought northwards by the Gulf Stream was about constant.

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