Keskiviikko 2.8.2023 klo 19:25 - Mikko Nikinmaa
We have been taught at school how the temperature in Central and Northern Europe is much higher than at similar latitudes elsewhere. The reason for this has been Gulf Stream, which flows northeast from the Gulf of Mexico to the Arctic, North of Norway. The stream moves a lot of heat from tropics to high latitudes. Finally the water cools and sinks to the bottom of the ocean and the cold water flows back south in southwest-directed cold streams. An important part of the dynamic water flow is that the Gulf Stream water sinks to ocean bottom, because that generates the driving force for water circulation. In the absence of water circulation, Central and Northern Europe would be much colder than presently, especially in winter. Gulf Stream water sinks, because when its temperature decreases to four degrees centigrade, the density of water is higher than the water below, which has a lower temperature. The density of water depends also on its salinity, the higher the salinity, the higher the density. Earlier on this has also contributed to the water circulation. The surface water flowing in Gulf stream from tropical areas has traditionally had higher salinity than the bottom water of the Arctic Sea.
Climate change is now threatening to change this warmth-bringing ocean circulation. The melting of Greenland glaciers but also the sea ice of the arctic causes a significant decrease in the density of surface water in the Arctic Sea. As a result, the sinking of Gulf Stream water from the surface to the bottom can be markedly reduced. This decreases the driving force for ocean circulation, and Gulf Stream may stop flowing altogether. The result for Central and North European climate would be that we experience Siberia-like weather patterns. An additional problem associated with presently ongoing freshwater addition is that the global temperature rise observed already seems to be adequate to cause continuing glacier melting in Greenland. This suggests that even if we are able to stop temperature increase to 1.5 degrees centigrade, the weakening of Gulf Stream may occur. There is no way to know, when we reach the tipping point.
So, if climate deniers tell you after three cold winters that clearly there is no climate change, as we have cold winters, you can answer them: “On the contrary, this shows that climate change has reached another tipping point. The heat transfer from tropics to the north in the form of Gulf Stream has stopped.” The real problem with this, and the weather patterns in general, is that what has happened and is happening is increased unpredictability. That is probably the biggest problem with climate change.