Scientists reported in a new study published Thursday that human-caused climate change has disrupted a large system of ocean currents in the Atlantic, including the Gulf Stream. If that system fails, it will cause dramatic changes in global weather patterns.
The Atlantic Meridional Overturning Circulation, or AMOC, transports warm, salty water from the tropics to the ocean surface and cold water to the ocean floor.
“The Atlantic Meridional Overturning is truly one of our planet’s key circulation systems,” said Niklas Boers of Germany’s Potsdam Institute for Climate Impact Research. Findings from a similar 2018 study drew comparisons to the scientifically inaccurate 2004 disaster film “The Day After Tomorrow,” which was based on such an ocean current shutdown. At the time, the study’s authors stated that a collapse was at least decades away but would be disastrous.
According to the authors of the new study, a potential collapse of this ocean current system would have far-reaching consequences around the world.
If this circulation fails, it could bring extreme cold to Europe and parts of North America, raise sea levels along the East Coast of the United States, and disrupt seasonal monsoons, which provide water to much of the world. It would also put the Amazon rainforest and Antarctic ice sheets in jeopardy.
Researchers studying ancient climate change have discovered evidence that the AMOC can abruptly shut down, causing wild temperature swings and other dramatic changes in global weather systems.
The study was published in the peer-reviewed British journal Nature Climate Change on Thursday.
Climate models show that the AMOC is at its weakest point in over 1,000 years. However, it is unknown whether the deterioration is due to a change in circulation or a loss of stability. “The distinction is critical,” explained Boers, “because the loss of dynamical stability would imply that the AMOC has approached its critical threshold, beyond which a significant and, in practice, likely irreversible transition to the weak mode could occur.”
Scientists determined that the recent weakening is likely related to a loss of stability by studying key data from the AMOC: “The findings support the assessment that the AMOC decline is not just a fluctuation or a linear response to increasing temperatures, but likely means the approaching of a critical threshold beyond which the circulation system could collapse,” Boers said. According to the study, a number of factors are likely to be important for the AMOC disruption – factors that add to the direct effect that warming of the Atlantic Ocean has on its circulation. Freshwater inflow from the melting Greenland ice sheet, melting sea ice, increased precipitation, and river run-off are examples of these.
Because freshwater is lighter than saltwater, it has a lower tendency to sink from the surface to greater depths, which is one of the causes of overturning.
According to other climate models, the AMOC will weaken over the next century, but a collapse before 2100 is unlikely.
“The study method cannot give us an exact timing of a possible collapse, but the analysis presents evidence that the AMOC has already lost stability, which I take as a warning that we might be closer to an AMOC tipping point than we think,” said Levke Caesar of Maynooth University in Ireland, who was not involved in the research.
Boers, the study’s lead author, told reporters that “It is one of those events that should not occur, and we should do everything possible to reduce greenhouse gas emissions as soon as possible. We don’t want to mess with this system.”