A major Atlantic Ocean current that helps regulate the climate across large parts of the Northern Hemisphere may be weakening more quickly than scientists previously believed, according to a study published recently in the journal Science Advances.
The current in question is the Atlantic Meridional Overturning Circulation, or AMOC. It works as a kind of conveyor belt, moving warm water from the tropics up toward the Northern Hemisphere and bringing colder water back down. The Gulf Stream is part of it.
This system is what keeps winters in Europe and Britain milder than they would otherwise be at those latitudes, and it plays a role in sustaining marine ecosystems.
Recalculating the Timeline
The new study projects that the AMOC will slow by between 43% and 59% by 2100. That’s roughly 60% greater weakening than the earlier CMIP6 multi-model (CMIP is a project of the World Climate Research Programme providing climate projections to understand past, present, and future climate changes) mean projections had suggested.
“This is a key result with implications for the future climate of the Atlantic and beyond,” the international team of researchers wrote in the paper.
If the AMOC were pushed past a tipping point into collapse, the consequences could last for hundreds or thousands of years. Sea levels could rise along the North American coast, and Southern Europe could face severe droughts. Scientists say the full risks depend on how far the system weakens and whether it crosses a tipping point.
Strengthening the evidence base
Several earlier studies have pointed in a similar direction. One recent companion study published in the same journal just days earlier found that AMOC strength had been declining across four ocean monitoring sites over the past two decades.
The new paper, however, takes a different approach in that it uses real-world observations to constrain model projections and folds in several variables at once, rather than relying only on the average of climate-model projections.
The team tested a number of statistical methods against various climate models. The most accurate combination, in their analysis, used what’s called ridge-regularized linear regression alongside a larger set of observed variables, including AMOC measurements, ocean temperature, and salinity data from multiple regions.
The method is rarely applied in climate modeling, but the researchers said it made the estimate much more precise, cutting the model uncertainty by 79% compared with the average across climate models. Using this approach, the team estimated the AMOC will slow by around 51% relative to its 1850 to 1900 average.
The paper notes that a slowdown of more than 50% would qualify as ‘substantial’ under IPCC (Intergovernmental Panel on Climate Change) terminology.
Other scientists, however, urged caution about taking the projections as definitive. “There remains uncertainty in how well models can simulate and predict changes in the AMOC,” said David Thornalley, a professor of ocean and climate science at UCL (University College London), who was not involved in the study.
María Paz Chidichimo, an ocean circulation researcher at the National University of San Martín in Buenos Aires, made a similar point. The findings of any single study, she said, need to be read against the broader literature. “I think the magnitude and timing of AMOC decline are still uncertain given the large spread in model projections,” she noted.
Sources: Science Advances, IPCC, Live Science, NYP, Science Advances Companion Study, PMC