What happens if the ocean conveyor belt stops

The researchers traced the start of the current's weakening to the midth century at the end of the Little Ice Age , a centuries-long period of extreme cold that froze northern Europe. When temperatures began warming up, freshwater from melting ice that flowed into the Nordic Seas would have diluted salty seawater near the surface. This weakened the current and prevented it from carrying bigger grains of sand as far as it used to, which told the scientists about differences in the current's strength, Oppo told Live Science.

Then, beginning in the s, another stage of warming and ice melt began in the Northern Hemisphere — this time, likely driven by human-induced climate change — infusing the sea with more chilly fresh water and further weakening the ocean circulation system, study lead author David Thornalley, a senior lecturer at University College London, told Live Science in an email. The research team estimated that, since the current began to lose strength in the mids, it has weakened by about 15 to 20 percent.

Another study, also published today in Nature , arrived at the same conclusions about a weakened AMOC — this time, by reviewing sea-surface temperature data going back to the late 19th century.

In this study, the researchers' temperature analysis confirmed computer models' predictions of AMOC behavior and suggested a decline of about 15 percent in current circulation strength, beginning in the s. The researchers detected an ocean temperature pattern that was a "fingerprint" for an AMOC slowdown: anomalous warming in the Gulf Stream and cooler waters near Greenland, suggesting that warm water was not being transported north as effectively as it once was, according to the study.

Though these two research teams used different methods, they arrived at a similar conclusion: that a crucial part of the climate system on our dynamic planet is not performing as it once did.

One of the effects of global warming is that polar ice caps are beginning to melt. As ice caps are composed of freshwater only, continual melting would cause the level of salinity in surrounding ocean waters to dilute.

Changes in salinity levels could affect thermohaline currents by preventing water from achieving enough density to sink to the bottom of the ocean. More seriously, ocean currents could stop completely. If ocean currents were to stop, climate could change quite significantly, particularly in Europe and countries in the North Atlantic.

In these countries, temperatures would drop, affecting humans as well as plants and animals. In turn, economies could also be affected, particularly those that involve agriculture. If these effects were to continue, Europe, North Atlantic countries and parts of North America could experience long periods of freezing conditions. However, if ocean currents halted as a result of global warming, these temperatures would also be affected by other aspects of the global-warming phenomenon.

This influx of fresh water could reduce the surface salinity and density, leading to a shutdown of the thermohaline circulation. Schlesinger and his team simulated the potential effects with an uncoupled ocean general circulation model and with it coupled to an atmosphere general circulation model. They found that the thermohaline circulation shut down irreversibly in the uncoupled model simulation, but reversibly in the coupled model simulation.

Doing nothing to abate global warming would be foolhardy if the thermohaline circulation shutdown is irreversible. Coauthors are U.