Anthropogenic warming may change the shape and behavior of North Atlantic winter circulation patterns without increasing their number. A 2026 Communications Earth & Environment study reports that climate forcing reorganizes the spatial characteristics of circulation regimes and produces different mid-tropospheric westerly changes in regimes dominated by positive and negative North Atlantic Oscillation (NAO) phases. The result is model-based, scenario-bounded, and not evidence that the entire jet stream shifts uniformly or that warming caused any particular storm.
What the study says about North Atlantic circulation
The 2026 Communications Earth & Environment study reports a change in the spatial structure of wintertime atmospheric circulation regimes over the North Atlantic under anthropogenic forcing. In its analysis, the number of regime states does not change, but their spatial characteristics do. It also finds contrasting future mid-tropospheric westerly changes in regimes dominated by positive versus negative NAO phases.
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That distinction matters. A circulation regime is a recurring pattern, not a fixed weather system. Reorganizing a regime means that its characteristic spatial pattern changes; it does not mean that a new regime necessarily appears, that one phase becomes more frequent, or that every part of the North Atlantic jet moves in the same direction.
The study uses one climate model and a high-emissions scenario. Its findings therefore describe a modeled response under those conditions, not a universal forecast across models or emissions pathways. The authors also note that responses may differ with the magnitude of forcing. The result should be read as evidence that warming can alter the structure of winter circulation patterns, not as a settled estimate of how often each pattern will occur in the real atmosphere.
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How the North Atlantic Oscillation connects to weather
The NAO is a recurring north–south dipole of pressure and atmospheric-height anomalies, with centers over Greenland and the central North Atlantic. Its positive and negative phases are associated with basin-wide changes in the location and intensity of the North Atlantic jet stream and storm track, and with changes in the transport of heat and moisture. NOAA’s Climate Prediction Center describes these circulation connections and their influence on weather patterns from eastern North America to western and central Europe.
Typical winter effects of positive and negative phases
In strong positive NAO winters, northern Europe and Scandinavia tend to be milder and wetter than average, while southern and central Europe tend to be drier. Strong negative phases are typically associated with the opposite precipitation pattern. These are broad tendencies, not deterministic forecasts for a specific location or winter: other circulation features and natural variability also affect local weather.
Because NAO phases relate to the jet, storm track, and heat and moisture transport, a change in the spatial form of a regime could matter even if the number of regime states stays the same. But the 2026 study’s reported structural change should not be treated as proof of a specific regional impact unless that impact is separately evaluated.
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Claims that the North Atlantic jet is changing are difficult to compare unless they specify what is changing. Latitude, wind speed, vertical shear, storm-track position, storm-track strength, and the shape of a circulation regime are different quantities. Evidence for a trend in one does not establish a trend in the others.
| Quantity | What it describes | Evidence and qualification |
|---|---|---|
| Regime structure | The spatial pattern of a recurring circulation state | The 2026 Communications Earth & Environment study reports wintertime reorganization under forcing, with no change in the number of regime states in its analysis. It is a one-model, high-emissions result. |
| Jet latitude | Where the jet’s strongest winds are located north to south | A 2012 Journal of Climate analysis found some model agreement on a poleward shift but considerable spread, particularly for winter. Results were sensitive to diagnostic methods and to the modeled response relative to biases against reanalysis. |
| Jet wind speed | The strength of winds at a selected level or location | A 2019 Nature study reported no change in North Atlantic polar-jet zonal wind speed at 250 hPa since the satellite era began in 1979. This observation does not rule out changes in other jet properties. |
| Vertical wind shear | How quickly wind speed changes with altitude | The same 2019 Nature study found a 15% increase in vertical shear, with a range of 11–17%, across three reanalysis datasets over the period it examined. The authors attributed the shear trend to the thermal-wind response to an enhanced upper-level meridional temperature gradient; this is not a 15% increase in jet speed. |
| Storm-track response | Changes in the strength, position, or extent of the band of traveling weather systems | Studies find regional responses and substantial model spread; storm-track change is not interchangeable with a shift in jet latitude. |
The observation of stronger vertical shear alongside no measured increase in jet speed illustrates why the metric matters. A headline about “a stronger jet” could incorrectly conflate these results. Likewise, model projections of a poleward shift do not negate a finding about changes in regime structure or storm-track extension.
Why ocean–atmosphere coupling adds uncertainty
The North Atlantic response is shaped by interactions between the atmosphere and ocean, not simply by a uniform poleward displacement of the jet. A 2012 Nature Geoscience study found that greenhouse-gas forcing could produce a storm-track response involving strengthening and eastward extension, especially along the southern flank, alongside an eddy-driven jet extension toward western Europe. Its experiments indicate that ocean–atmosphere coupling shapes this regional pattern.
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In that study’s model ensemble, at least half of the differences among storm-track responses were associated with uncertainty in ocean-circulation changes. The authors argued that tighter constraints on future ocean circulation could reduce uncertainty. That result helps explain why two climate models can project different North Atlantic responses to similar forcing; it is not a quantitative forecast of future storm damage in Europe.
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Broader circulation changes provide context but should not be mistaken for a North Atlantic-specific attribution. A 2017 U.S. Global Change Research Program assessment chapter, summarized by NASA GISS, reported that the tropics expanded poleward by about 70 to 200 miles in each hemisphere from 1979 to 2009, alongside shifts in subtropical dry zones, midlatitude jets, and storm tracks. The assessment judged a human role with medium confidence, but confidence in the magnitude of that role relative to natural variability was low.
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What very long-range projections do—and do not—show
A separate 2026-issue study in npj Climate and Atmospheric Science examined a CMIP6 long-term extension of the high-emissions SSP5-8.5 scenario, with greenhouse gases continuing to rise beyond 2100. In that experiment, the North Atlantic winter storm track and jet intensify through the mid-22nd century, then weaken even as CO2 continues to increase. The study links the reversal to the logarithmic relationship between CO2 and temperature and the resulting reduction in the meridional temperature gradient at very high CO2.
| Period in the study’s experiment | Storm-track change | Jet change | Reference and scope |
|---|---|---|---|
| 2140–2160 | About 14% intensification | About 7% intensification | Relative to 1990–2010 in the specified CMIP6 SSP5-8.5 long-term extension; reported by the 2026-issue npj Climate and Atmospheric Science study. |
| 2280–2299 | About 3% increase | About 0.2% increase | Relative to 1990–2010 in the same experiment; these are not near-term predictions or consensus ranges. |
These distant-future percentages belong to that study’s scenario and model experiments. They should not be used as estimates for the coming decades, nor generalized into a claim that North Atlantic circulation must strengthen first and weaken later under every emissions pathway.
How to interpret a claim about North Atlantic circulation
When comparing findings about the North Atlantic jet stream under climate change or the storm-track response, check whether they concern winter or another season, what circulation quantity they measure, and whether the evidence is observational or model-projected. Also check the model and ocean-coupling setup, the forcing scenario, and the time horizon. These distinctions explain why one study can report a change in regime shape, another can find little observed change in jet speed, and another can project a long-range storm-track reversal without the results contradicting one another.
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- Regime structure is not regime frequency: a spatial reorganization does not by itself establish that positive or negative NAO phases become more common.
- Jet latitude is not jet speed or shear: each is a separate diagnostic, with its own evidence and uncertainties.
- A forced model response is not a single-event attribution: circulation influences regional weather, but an ensemble-scale result alone cannot establish why a particular storm or local impact occurred.
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