{"id":413569,"date":"2025-11-17T09:45:02","date_gmt":"2025-11-17T08:45:02","guid":{"rendered":"https:\/\/climatescience.press\/?p=413569"},"modified":"2025-11-17T09:45:05","modified_gmt":"2025-11-17T08:45:05","slug":"nature-claims-their-circulation-is-decreasing","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=413569","title":{"rendered":"Nature Claims Their Circulation Is Decreasing"},"content":{"rendered":"\n
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Watts Up With That?<\/a><\/p>\n\n\n\n

Guest Post by<\/em><\/strong> Willis Eschenbach<\/a> (@WEschenbach on X)<\/em><\/strong><\/p>\n\n\n\n

Let\u2019s get something straight: this new study entitled Equatorial Atlantic mid-depth warming indicates Atlantic meridional overturning circulation slowdown<\/a>, <\/strong>hot off the Nature presses and already getting the full catastrophe-trending treatment, claims that mysterious \u201cmid-depth warming\u201d in the equatorial Atlantic\u2014between 1,000 and 2,000 meters down\u2014is the long-sought \u201cfingerprint\u201d proving that the Atlantic Meridional Overturning Circulation (AMOC) has been slowing since the 1990s.<\/p>\n\n\n\n

According to the authors, this subsurface warming is more \u201creliable\u201d than surface measurements, cleaner than the noise-soaked sea surface temperatures everyone\u2019s been arguing about for years, and\u2014conveniently\u2014it fits right into the climate alarm narrative that the AMOC is heading for catastrophic collapse. If you buy this story, you\u2019re supposed to panic now, because the collapse might already be underway, the tipping point looms, and we\u2019re all headed for Day After Tomorrow ice-age-in-a-week horror.<\/p>\n\n\n\n

There\u2019s just one problem: the whole edifice is built on model outputs, selective data interpretation, circular reasoning, and a studied refusal to acknowledge that the AMOC might be doing just fine.<\/p>\n\n\n\n

Let\u2019s start with the foundation. The authors run the MIT General Circulation Model (MITgcm) using forcing data pulled from CMIP6 climate model simulations under a quadrupled CO\u2082<\/a> scenario\u2014because apparently we needed more hypotheticals stacked on hypotheticals. Of course, there\u2019s not enough fossil fuels<\/a> on the planet to lead to a quadrupled CO\u2082 level, but pay no attention to the man behind the curtain \u2026<\/p>\n\n\n\n

Then they impose abrupt changes in wind stress, sea surface temperature, and sea surface salinity, taken straight from models that already assume an AMOC slowdown, and\u2014surprise!\u2014the model dutifully spits out a slowdown and equatorial warming. It\u2019s the scientific equivalent of asking a parrot to repeat what you just taught it, then claiming the parrot discovered language.<\/p>\n\n\n\n

The \u201cexperiments\u201d (BUOY, BUOY-NA, SSS-NA) are all variations on a theme: fiddle with surface forcing, watch the model respond in pre-cooked ways, then cherry-pick the results that support the thesis. Want mid-depth warming? Easy\u2014force in North Atlantic freshening (which the CMIP6 models already baked in as part of their AMOC-weakening scenarios), sit back, and let \u201cbaroclinic Kelvin waves\u201d do the propagation magic. It\u2019s not an independent test of the hypothesis; it\u2019s a self-fulfilling simulation.<\/p>\n\n\n\n

The study\u2019s logic runs in a perfect circle.<\/p>\n\n\n\n

Step one: assume the CMIP6 models (which all project AMOC weakening under CO\u2082 forcing) are correct.<\/p>\n\n\n\n

Step two: use those same models\u2019 outputs as forcing for your ocean model.<\/p>\n\n\n\n

Step three: when your ocean model shows equatorial warming, declare that this warming is the \u201cfingerprint\u201d of AMOC slowdown.<\/p>\n\n\n\n

Step four: find warming in the observational data.<\/p>\n\n\n\n

Step five: conclude the AMOC must be slowing because you found the \u201cfingerprint.\u201d<\/p>\n\n\n\n

At no point do they test whether the warming could be driven by anything other<\/em> than AMOC changes\u2014such as, oh, I don\u2019t know, local wind patterns, El Ni\u00f1o teleconnections, subsurface advection from other basins, or the natural variability that the equatorial Atlantic is famous for.<\/p>\n\n\n\n

The authors triumphantly point to warming trends in gridded datasets (WOA, Argo, IAP, Ishii, EN4) showing 0.14\u00b0C of mid-depth warming from 1960 to 2020. Sounds impressive until you realize: (1) pre-1980 subsurface data in the equatorial Atlantic is sparse, riddled with gaps, and heavily interpolated; (2) Argo floats only started coverage in 2004, so the \u201crobust\u201d trend is mostly a post-millennial artifact; and (3) the \u201csignal-to-noise\u201d ratio they\u2019re so proud of is high precisely because<\/em> mid-depth waters have high thermal inertia\u2014meaning the warming could be a slow, cumulative response to anything<\/em>, not necessarily AMOC changes.<\/p>\n\n\n\n

Moreover, the study conveniently ignores a major new finding<\/a> <\/a>published just this year in Nature<\/em>: an independent reconstruction using air-sea heat flux data concluded that the AMOC has not declined over the past 60 years<\/strong> and is more stable than previously thought. That study, from Woods Hole, directly contradicts the premise here and suggests that relying on SST proxies (the very thing this new study is trying to replace) was always the problem\u2014not because the AMOC is weakening, but because SSTs are lousy proxies in the first place.<\/p>\n\n\n\n

Yes, baroclinic Kelvin waves are real, and yes, they can propagate warming signals from the subpolar North Atlantic down the western boundary and across the equator. The authors make a big deal about \u201crapid adjustment\u201d and \u201cdynamical signals,\u201d invoking vertical mode decomposition and wave speeds to lend scientific gravitas. But here\u2019s what they don\u2019t tell you: the equatorial Atlantic is also subject to wind-driven upwelling, Atlantic Ni\u00f1o\/Ni\u00f1a variability, off-equatorial Rossby wave adjustments from the northwestern<\/em> tropical Atlantic (not the subpolar regions), and teleconnections from the Pacific. Multiple studies have shown that equatorial Atlantic warming is more consistently linked to local and regional processes\u2014especially wind stress curl anomalies associated with the Atlantic Meridional Mode\u2014than to remote AMOC forcing.<\/p>\n\n\n\n

The fact that their passive tracer experiment (BUOY-NA-passive) shows minimal mid-depth warming from mean circulation alone doesn\u2019t rule out these other mechanisms\u2014it just means their model setup didn\u2019t include them.<\/p>\n\n\n\n

The authors claim the warming \u201cemerged\u201d from natural variability around 2001, with a signal-to-noise ratio exceeding their arbitrary threshold of 4 (99.9% confidence). But \u201ctime of emergence\u201d is a model-dependent metric that depends entirely on how you define \u201csignal\u201d and \u201cnoise.\u201d They define signal as the linear trend and noise as detrended variability\u2014which guarantees that any long-term drift, regardless of cause, will eventually \u201cemerge.\u201d It\u2019s a statistical trick that makes any monotonic change look significant if you wait long enough.<\/p>\n\n\n\n

The study buries or ignores inconvenient facts. For instance:<\/p>\n\n\n\n