A vital system of ocean currents that governs weather patterns across the northern hemisphere could collapse by the middle of the century and potentially as early as two years’ time, according to a study warning that the ocean climate system is close to an irreversible tipping point. But other researchers have doubts about the accuracy of the projections.

The Atlantic meridional overturning circulation (AMOC) is a large system of ocean currents that acts like a conveyor belt, carrying warm water from the tropics into the North Atlantic. Scientists have already warned that climate change is weakening the AMOC and say the system could potentially collapse in the future. But the strength of the AMOC has only been consistently monitored since 2004, leaving researchers without enough long-term data to make clear estimates of when such a collapse might occur.

The Intergovernmental Panel on Climate Change (IPCC) says a full AMOC collapse is unlikely in the current century, based on climate modelling. In their new study, siblings Peter and Susanne Ditlevsen, both at the University of Copenhagen, Denmark, used sea surface temperature data from the sub-polar North Atlantic – which dates back to 1870 – as a proxy for the stability of the AMOC.

To read the full review published in New Scientist click here.

The last time the AMOC switched modes during the most recent ice age, the climate near Greenland increased by 18 to 27 degrees Fahrenheit (10 to 15 degrees Celsius) within a decade. If it were to turn off, temperatures in Europe and North America could drop by as much as 9 F (5 C) in the same amount of time.

Direct data on the AMOC’s strength has only been recorded since 2004, so to analyse changes to the current over longer timescales, the researchers turned to surface temperature readings of the subpolar gyre between the years of 1870 and 2020, a system which they argue provides a ‘fingerprint’ for the strength of AMOC’s circulation.

By feeding this information into a statistical model, the researchers gauged the diminishing strength and resilience of the ocean current by its growing year-on-year fluctuations.

“If the statistics are robust and are a correct/relevant way to describe how the actual modern AMOC behaves, and the changes relate (solely) to changes in the AMOC, then this is a very concerning result,” David Thornalley, a professor of ocean and climate science at University College London, told Live Science in an email. “But there are some really big unknowns and assumptions that need investigating before we have confidence in this result.”

Other climate scientists have gone so far as to pour cold water on the findings, suggesting it is “wholly unclear” that observed surface temperature evolution of AMOC can be linked to the strength of its circulation.

To read the full review published on Live Science click here.

The paper, published in Nature Communications, is available here.