The Atlantic current that keeps Europe mild has been weakening for two decades

The deep western limb of the Atlantic Meridional Overturning Circulation, the system of currents that carries warm water north and underpins mild winters in northwestern Europe, has declined at three of four monitoring sites from the tropics to the mid-latitudes, a study in Science Advances reports. Shane Elipot of the University of Miami’s Rosenstiel School and five co-authors, including David Smeed and Ben Moat of the UK’s National Oceanography Centre, pulled the sites together into one analysis covering 2000 to 2023.

The finding is a measured trend at the western edge of the Atlantic, not a verdict on the whole circulation, and the paper is explicit about what that leaves open. The study was published April 8, 2026.

MOVE, RAPID-MOCHA, Line W and RAPID-Scotian

The authors are Qianjiang Xing, Elipot, William Johns, Smeed, Moat and John Loder, and their paper is titled “Meridionally consistent decline in the observed western boundary contribution to the Atlantic Meridional Overturning Circulation.” Its data come from four mooring arrays along the western boundary, listed in the open-access copy of the paper: MOVE at 16.5°N (2000 to 2022), RAPID-MOCHA at 26.5°N (2004 to 2023), Line W at 39.5°N (2004 to 2014) and RAPID-Scotian at 42.5°N (2008 to 2014).

The record lengths therefore differ by a lot, from about 23 years at the southern end to six at the northern end. “Two decades” describes the combined window and the two longest arrays, MOVE and RAPID-MOCHA, not each site. The two northern arrays ran for roughly a decade or less, and the northernmost is the one trend that fails the significance test. That ordering matters for how far the two-decade framing can be pushed: the two-decade claim is strongest in the tropics and subtropics, where the instruments have been in the water the longest.

Three significant declines and one that is not

The paper reports trends in Sverdrups per year, with 2-sigma confidence intervals: 0.67 plus or minus 0.13 at MOVE, 0.26 plus or minus 0.07 at RAPID-MOCHA and 0.45 plus or minus 0.17 at Line W. All three are statistically significant. At the northernmost array, RAPID-Scotian, the figure is 0.10 plus or minus 0.17, a decline that cannot be distinguished from zero at that confidence level.

The University of Miami’s announcement of the study says the instruments sit on the seafloor and measure pressure, temperature, density and currents below 1,000 meters, and that the decline is consistent across latitudes. Elipot, a physical oceanographer, is quoted there on what a weaker circulation could mean: shifted weather patterns, potentially more extreme storms, changed rainfall, or colder winters in some regions.

Eastern-boundary offset and the short-record problem

The caveat the paper itself carries is that the signal reflects changes at the western boundary only, and that the eastern boundary appears to have affected the total trend significantly. At 26.5°N, the eastern side has been strengthening at 0.16 plus or minus 0.06 Sverdrups per year, which partially offsets the western decline. The observational records are also relatively short, which limits any judgment about whether the declines are a long-term trend or decadal variability.

That offsetting is visible in the best-known single series. The RAPID team at the National Oceanography Centre reported in its 20-year update a weakening of 0.9 plus or minus 0.7 Sverdrups per decade at 26°N for the total circulation. Moat, who leads the center’s open ocean physics team, said continued observing through at least 2034 is crucial to ascertain the trend and to separate natural variability from human-caused change.

The case for calling it the current that keeps Europe mild

The “keeps Europe mild” description rests on heat transport. The RAPID-MOCHA programme, which has run since 2004 under National Oceanography Centre leadership with partners including the University of Miami and NOAA, states that the circulation carries 1.2 petawatts of heat northward, about a quarter of the global atmosphere-ocean poleward total. The same programme documented a significant downturn beginning in 2010 and 2011, followed by a sustained decline, and brief reversals on short timescales.

The study itself does not project what a continued decline would do to European winters. The Miami announcement lists altered European winters, modified hurricane activity, changed rainfall and sea-level rise as possible consequences, and credits funding from the U.S. National Science Foundation and the UK’s Natural Environment Research Council. A September repost of the findings put the work back in front of readers, but the measurements and analysis date to the spring paper, and the 42.5°N record remains the one array whose trend the authors cannot distinguish from no change. A claim that the whole circulation has weakened for two decades would need the eastern side of the basin in the tally, and that is the piece of the budget this paper leaves out.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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