Science1 publisher2 min readPublished
Three climate models tie a slightly longer day to warming's rearranged winds
Susmit Satpathy's team finds that warming-driven winds lengthen Earth's day by about 10-18% of the long-term tidal-friction trend by 2100 in three climate models. The study gives a physical cause for the atmosphere's projected gain in angular momentum, which adds a small amount to the slowing that tides already cause.
The Scientist · Science desk
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What happened
- The team ran large ensembles of simulations from three different global climate models under a high-emissions scenario.
- The models consistently show the Hadley cell expanding poleward, subtropical jets intensifying, trade winds weakening and upper-level zonal winds strengthening.
- Momentum exchange between the atmosphere and the solid Earth also weakens at the surface, leaving the planet less able to keep up with the changing air, the authors say.
- Tidal friction, the benchmark the authors chose for scale, has long been considered the dominant driver of Earth's long-term rotational slowing.
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Why it matters
- constraint Every figure in the study belongs to a high-emissions future, so a lower-emissions pathway would need its own simulations before anyone could attach a number to it.
- capability With the angular-momentum gain traced to named circulation changes, each model's rotation estimate can be checked against how well that model simulates its jets and Hadley-cell width.
- precedent Long-term rotation budgets that have treated tides as the steady slowing force and the core as the main source of variability now have a modelled climate term to carry as well.
Earlier projections already had the atmosphere gaining angular momentum as the planet warms. They had not settled the cause: stronger winds alone, or a deeper restructuring of the circulation [6]. This study's answer is restructuring. The circulation shifts are well-known responses to warming, and the authors find that together they raise atmospheric angular momentum systematically [4]. Because the air and the solid Earth trade momentum [12], the gain shows up as a slightly faster-moving atmosphere over a slightly slower-turning planet [13].
The design is the strength of the study. Any one model's answer can be an artefact of its own physics, so getting the same picture from three different models matters [2]. The authors call the effect "a systematic, externally forced signal, not just internal variability" [8]. That claim depends on the large ensembles: with many runs per model, a forced trend can be separated from random weather [2].
"The changes we identify are subtle," the authors wrote [16]. Turned around, their benchmark says the long-term tidal friction trend is roughly 5.6 to 10 times the size of the atmospheric contribution at the end of the century [1]. They are careful about that comparison: "Our comparison is not intended to suggest equivalence, but to provide a physically meaningful benchmark for interpreting the magnitude of the atmospheric contribution" [10]. The researchers' summary does not state the change in milliseconds of day length.
The thing this doesn't tell you is whether the effect will show up in measured day length. Interactions between Earth's core and mantle dominate rotation variability over decades to centuries, according to recent studies the authors point to. The paper treats the atmospheric change as one additional, climate-driven part of that system [9].
In my view the attribution is the advance here, and the size of the effect matters less. That view holds only as long as the models simulate the underlying circulation shifts well. The account comes from Science X Dialog, where researchers describe their own published work [15], so the framing is the authors' own. The peer-reviewed paper appeared in npj Climate and Atmospheric Science in 2026 [1]. Its first author, Susmit Subhransu Satpathy, recently completed his PhD at the IBS Center for Climate Physics at Pusan National University [14].
What to watch
- Studies that try to separate a slow climate-driven term from core-mantle variability in measured length-of-day records.
- Independent model groups reproducing the weakening of surface momentum exchange between the atmosphere and the solid Earth, the least familiar part of the result.