More Science About Possibly Weakening North Atlantic Current. North Atlantic weather patterns are ruled by an ocean circulation system. Warm waters coming from tropics are yielding a mild climate along western Europe and Labrador coasts. Such a pattern is better known as "Gulf Stream". Further studies showed that this current pattern has an underwater part, starting about Labrador and bringing cold water back to tropics. Lately, Pentagon defense adviser Andrew Marshall, an old-timer and influential adviser of Kennedy and Nixon eras, commissionned a report. This report was forecasting doomsday next day as an abrupt climate change in the coming 20 years would bring planet to the edge of anarchy. A part of the threat was linked to changes in North Atlantic currents. Drastic changes would bring a Siberia climate to western Europe and northeastern USA. As far as this part of the troubles is concerned, North Atlantic currents modification would be yielded by perennial Arctic ice thawing. An addition of fresh water either directly, either under the form of increased precipitations in the region would render waters there more buoyant. Such buoyant water would not sink anymore, hindering Gulf Stream process

Late NASA and Goddard Space Flight Center study -published in Science magazine- is showing that there really is a problem in North Atlantic Ocean. A thorough study of North Atlantic Ocean circulation system's part which is dubbed the "sub polar gyre" is showing that this current weakened considerably in the late 1990s compared to the 1970s and 1980s. Sub polar gyre belongs to Gulf Stream system. It is moving water in a counterclockwise pattern from Ireland to Labrador. Once there waters are plunging downwards, heading back slowly to equator as an intermediate depth current. Such a journey may take about 20 years. Sub polar gyre is sensitive to local weather conditions and particularly to perennial ice Arctic melting. A modification of this current might bring a change to North Atlantic climate system and perhaps to global climate. Waters in the 1990s have been found warmer about Labrador, decreasing contrast with warmer southern latitudes waters, hence reducing the driving force behind ocean circulation. Until now a sub polar gyre weakening had already be observed but was linked to oscillations of a large-scale atmospheric pressure system known as the North Atlantic Oscillation (NAO), and considered normal. Late study is showing that current weakening continued despite the fact that NAO switched twice in the 1990s. Sub polar gyre might have an evolution of its own. Scientists are stressing that they need a further 5 to 10 years to definitively assess what is going on: is current weakening part of a natural cycle or is it resulting of factors related to global warming? main story is at Goddard Space Flight Center: http://www.gsfc.nasa.gov/topstory/2004/0415gyre.html

On another hand, other factors are at work in Atlantic Ocean as a large-scale sea currents system seems to link Pacific Ocean to Atlantic Ocean through Indian Ocean. Such a pattern, known as the "Great Ocean Conveyor" is somehow a larger Gulf Stream system. Working on a 15-20 year cycle Great Ocean Conveyor is transporting warm water from Pacific Ocean into Atlantic. When such a conveyor is active, Atlantic Ocean climate is warmer and wetter as Pacific Ocean one is colder and dryer (El Niño phenomenon). And the reverse (El Niña in Pacific Ocean) when conveyor is inactive. A warmer Atlantic Ocean climate usually means an increased hurricanes rate. As far as this cycle is concerned we should now have entered an active phase since about 1995. Great Ocean Conveyor does not seem to be concerned by Arctic ice thawing in its Pacific Ocean part. Waters there are just cold water rising to surface, and where the phenomenon takes place is far South Bering Strait. Nor is it by a possible Antarctic thawing neither, as cold eastwards current there is just an underwater one all along Antarctic coasts, from South America to Australia