A Climate Change Amplifying Mechanism Linking Polar to Tropical Regions through Oceanic Circulation
28.02.2007 - Other
In the past alternating glacial and subglacial periods resulted in a modification of global oceanic circulation. Scientists at CEREGE1 have highlighted a feedback mechanism of ocean circulation on the climate reinforcing heating or cooling.
Climatic archives (marine and lake sediment, polar ice, stalagmites) show the close relationship existing between climatic variations and oceanic circulation. Changes in oceanic circulation in the North Atlantic have influence on a planetary level by affecting, in particular, the water cycle. These changes are accompanied by a shift in the climatic equator which separates the trade wind systems of the two hemispheres: southwards during cold events and northwards during hot ones. Scientists have discovered a feedback mechanism amplifying the climatic disturbance.
During warm periods, these trade winds loaded with humidity coming from the evaporation of the Atlantic Ocean discharge it as rain on the Eastern Pacific after having crossed the Central American isthmus. The saltier surface waters of the tropical Atlantic are then transported, via the Gulf Stream, towards the high latitudes where they warm the atmosphere before plunging into the abysses in the convection zones situated in the seas of Norway, Greenland and Labrador. The deep waters formed by this process then flow into the world ocean, purging the North Atlantic of part of its excess salt.
During cold periods, trade winds, loaded with humidity, migrated southwards. Unable to cross the Andes, part of the rain, which would normally have lowered the salinity of the East Pacific, fell in the Amazon basin, re-injecting rainwater into the Atlantic ocean and decreasing its salinity. This water was then transported to the higher latitudes, contributing to the weakening of deep oceanic circulation, thereby reinforcing the cooling above and around the North Atlantic.
Today, the fact that global warming could disturb the water cycle and lead to a slowing down of the North Atlantic circulation is a real subject of concern. Such feedback mechanisms show that the risk of an even greater variation of oceanic circulation by the end of this century or the beginning of the next needs to be taken seriously and actively studied.
