Temperatures could drop drastically and permanently in the Northern Hemisphere due to a weakening ocean currents.A new study suggests that one of the most important ocean current systems in the regulation of the Northern Hemisphere's climate may be at risk of total collapse as a result of climate change.According to a new analysis, the Atlantic Meridional Overturning Circulation has suffered "an almost total loss of stability over this century". This includes the Gulf Stream. It is responsible for regulating large parts of the climate. They act like a conveyor belt, transporting warm, salty water northwards from the tropics and cool water south along the seafloor. The giant conveyor belt was already shown to be at its weakest for more than 1,000 years. However, it may be heading towards total collapse.According to the U.K. meteorological office, such a collapse could have devastating effects on global weather systems. It would cause sea-level rises in Atlantic, greater cooling, and stronger storms across the Northern Hemisphere, and disrupt rains that billions depend upon to grow crops in Africa and South America.Related: 10 signs the Earth's climate has gone off-trackAccording to the study author, this transition could happen quickly after the ocean current system has reached a critical tipping point."The findings support that the AMOC decrease is not just fluctuation or a line response to increasing temperatures, but likely signifies the approaching of the critical threshold beyond which circulation system could collapse," Niklas Boers (a researcher at Potsdam Institute for Climate Impact Research, Germany) stated in a statement.Past analyses of Atlantic Ice Cores and other geological records have shown that the AMOC can exist both in stable states. One is stronger and faster than what humans depend on today, while another is slower and weaker. Boers believes that the existence of these two states means that it is possible to make "abrupt transitions" between the two circulation modes.The current could become weaker until it reaches a tipping level, switching from the stronger to the weaker state. This will quickly change the climates in the Northern Hemisphere, making them much more temperate than they currently are.The Gulf Stream current, red in color, moves warm water along the east coast of the United States. It clashes with the North Atlantic cold water. NASA Earth Observatory. Image credit.This new study attempts to settle a controversial topic among oceanologists: whether recent weakening of the AMOC means that it will circulate slower but in a way that humans are able to reduce carbon emissions or if it means that the AMOC is about flipping to a permanently weaker version that cannot be reversed for hundreds upon hundreds of years.Boers stated that "the difference is crucial." If it is the latter, this would indicate that "the AMOC has reached its critical threshold beyond which a substantial, and in practice likely irreversible, transition to the weaker mode could occur."Bad news for the planet: After analyzing the Atlantic Ocean's sea-surface temperature patterns and salinity patterns, researchers concluded that the recent weakening was more likely to be related to an irreversible loss in stability.Because the AMOC relies on salty water from the south to circulate, and to allow colder norther water to sink below it. To keep the cycle running, the water from the south must be denser than that from the north.The temperature and saltiness of ocean water determine the density. The current is currently more salty in the southern region, which becomes colder and denser with increasing latitude. The southern waters cooling to the same temperature as the northern waters they flow towards, the added salt density allows the water flowing to the south to sink to the bottom of the less salty north water. This causes it to push it southwards in a global conveyor belt.The current is sinking less and becoming less dense as a result of the warmer temperatures and freshwater inflow from melting ice sheet. Researchers said that this could cause the AMOC to cease completely and lead to a drastic and irreversible shift of global climate systems.Boers believes that scientists may have reached the critical threshold before collapse happens sooner than originally thought.Boers stated that he didn't expect that excessive freshwater additions over the past century would result in such a response to the overturning circulation. "We need to immediately reconcile our models and the observed evidence to determine how far away or close to the critical threshold that the AMOC is."The team stated that although the strengths of different factors contributed to the current's slowing were still being weighed against one another, they all had a connection to human-caused climate changes.August 5, 2009, was the publication date for the findings by the researchers in Nature Climate Change.Original publication on Live Science
