New research has revealed the Atlantic Ocean circulation system that moderates temperatures in Europe is weaker than at any point in the last 1,600 years. Previous predictions suggested a collapse of the current would not occur for centuries, but the new findings suggest the system is less stable than scientists thought.
Scientists believe the changes are due to an increasing amount of freshwater on the ocean’s surface from melting ice sheets. If it continues to weaken, the current could cause disruption to global weather patterns resulting in colder temperatures in the North Atlantic and northwest Europe.
The warm Atlantic current, known as the Atlantic Meridional Overturning Circulation (Amoc), is believed to impact the global climate and has been linked to abrupt climate changes in the past. Amoc brings warm, salty water in the Atlantic towards the North Pole. The water then cools, increases in density, sinks and begins to flow back towards the south.
Rising global temperatures slow down the current in two ways: by impeding the cooling of the water in the North Atlantic and by increasing the amount of less dense freshwater that enters the area due to melting ice.
The new study, published on Wednesday in the journal Nature, was conducted by researchers at University College London (UCL) and Woods Hole Oceanographic Institution (WHOI) in Massachusetts.
To investigate Atlantic circulation strength over the past 1600 years, researchers collected long cores of sediment from the ocean floor and looked at the size of sediment grains deposited by deep-sea currents. Larger grains of sediments indicate faster Amoc currents, while smaller grains reflect slower currents. The team found that Amoc has weakened by around 15-20% over the past 150 years.
“This weakening of the Atlantic’s overturning began near the end of the Little Ice Age, a centuries-long cold period that lasted until about 1850,” Dr Delia Oppo, co-author of the study and a senior scientist at WHOI, told Forbes.
The scientists said initial slowing of the current was caused by natural variations in climate, but that subsequent weakening of the system was due to recent global warming.
Their findings were supported by another study also published on Wednesday in Nature. The second study, led by researchers from Germany’s Potsdam Institute for Climate Impact Research, used climate model data to show that spatial and seasonal sea-surface temperature patterns reflect the strength of Amoc. Although the team’s results confirmed the current has been weakening, they suggest the system has been slowing down at an increasing rate since the 1950s due to human-induced climate change.
Both teams agreed that global warming would likely continue to weaken Amoc, a trend that could have serious impacts on weather patterns and marine ecosystems.
“If we do not rapidly stop global warming, we must expect a further long-term slowdown of the Atlantic overturning,” said Alexander Robinson of the University of Madrid, who co-authored the second study. “We are only beginning to understand the consequences of this unprecedented process – but they might be disruptive.”
Scientists said that in addition to altering global weather patterns, further weakening of the current could affect fragile deep-ocean ecosystems and impact species including coral and Atlantic cod.