The study uses 100 members of the CESM2 Large Ensemble (under the high- emissions SSP3-7.0 scenario) for winter (DJF) 500 hPa stream function over the North Atlantic (1850- 2100).

It separates the full flow field (forced response and internal variability) from pure internal variability (by subtracting the ensemble mean).

• A changepoint analysis detects a clear anthropogenic imprint on mid- tropospheric circulation around 1995. Analyses therefore compare pre-1995 vs. post-1995 periods.
• With the forced response included, the number of atmospheric regime states stays the same (four regimes both before and after 1995). However, their spatial patterns reorganise substantially: high- and low- pressure centres shift northward, some circulations intensify, and the overall phase- space distribution shifts.
• Internal variability alone shows a reduction in the number of regime states after 1995, with one regime becoming more persistent, suggesting anthropogenic warming suppresses some natural variability.
• Future projections show a shift toward more frequent positive North Atlantic Oscillation (NAO) phases through much of the 21st century, accompanied by more low- amplitude negative NAO phases late in the century. Overall NAO variability declines markedly, and mid- tropospheric westerlies are altered (strengthened in positive-NAO regimes, weakened in negative ones).

Methods highlights

The authors apply Singular Value Decomposition (SVD) between 500 hPa stream function and surface temperature to capture coupled variability (preferred over standard EOFs for isolating the forced signal). Regime identification uses clustering on the leading principal components. The large ensemble allows robust separation of forced change from internal variability and detection of multimodality that single realizations often miss.

Broader context and implications

Atmospheric regimes (quasi- stationary, recurring circulation patterns) strongly influence North Atlantic weather, including European winter storms, temperature extremes, precipitation, and the NAO itself. The results indicate that climate change does not simply make existing patterns more frequent or “warmer”; it reorganises their spatial structure and damps natural variability. This has implications for seasonal prediction, climate risk assessment, wind energy, ecosystems, and adaptation planning in Europe, eastern North America, and the Arctic.

The paper is directly and extensively about the North Atlantic Oscillation (NAO), while its connection to Arctic amplification is more indirect and conceptual rather than explicit.

Strong, direct relationship to the NAO

The NAO is a central focus of the study. The authors treat it both as a key component of North Atlantic atmospheric regimes and as a distinct mode whose behaviour changes under anthropogenic warming.

Key NAO- related findings include:

• Atmospheric regimes over the North Atlantic include NAO- like patterns (zonal/positive and blocked/negative phases). The post-1995 period shows a more prominent NAO- positive-like structure in the ensemble- mean circulation (strengthened Icelandic Low and Azores High).
• Under the forced response (full flow field), the number of regimes stays constant (four), but their spatial organisation shifts northward. Extreme NAO- negative- like regimes become somewhat more frequent in the later period.
• Future projections show a shift toward more frequent positive NAO phases through much of the 21st century. This is accompanied by an increase in low-amplitude negative NAO events late in the century, a marked decline in overall NAO variability, and changes in mid- tropospheric westerlies (strengthened under positive NAO regimes, weakened under negative ones).
• The forced response of the NAO index itself exhibits a statistically significant positive trend that partially reverses near the end of the century.
• The NAO is linked to regime transitions and persistence: inter- regime connectivity weakens under warming while certain regimes (including those related to NAO) become more persistent.
• The model (CESM2-LE) reproduces observed NAO characteristics reasonably well, with the observational index falling within the ensemble spread.

In short, the paper argues that anthropogenic warming reorganises the preferred circulation states (regimes) of which the NAO is a dominant expression, rather than simply changing the frequency of the classical NAO modes in isolation.

Relationship to Arctic amplification

The paper does not explicitly discuss or quantify “Arctic amplification” (the disproportionately rapid warming of the Arctic relative to the global mean). There is no direct analysis of polar temperature gradients, Arctic sea- ice loss as a driver, or the classic “Arctic amplification → weaker meridional gradient → altered jet/NAO” pathway.

However, several findings sit in the broader scientific context where Arctic amplification is often invoked:

• The study notes that NAO phases influence Arctic sea-ice variability (and vice versa in coupled systems).
• Northward displacement of cyclonic and anticyclonic centres under warming is consistent with the poleward shifts of the jet stream and storm tracks that many studies attribute partly to tropical upper-tropospheric warming competing with (or sometimes opposing) Arctic amplification effects.
• The reorganisation of mid-tropospheric circulation and the damping of internal variability could be influenced by the changing high- latitude temperature structure, although the authors attribute the detected changes primarily to the overall anthropogenic forced response (greenhouse gases, aerosols, etc.) rather than isolating Arctic processes.
• Surface temperature patterns associated with the regimes show features such as the North Atlantic Warming Hole, which interacts with high- latitude dynamics.

Arctic amplification is a well- known mechanism that can weaken the meridional temperature gradient, potentially favouring a more negative NAO or weakened westerlies in some seasons.

The paper’s finding of a shift toward more positive NAO phases (with reduced variability) is therefore interesting in that context, it aligns more with the competing influence of tropical amplification and upper- level warming that tends to strengthen and poleward- shift the jet, rather than a pure Arctic- amplification- driven response. The large- ensemble approach allows the authors to isolate the forced signal without needing to attribute it specifically to Arctic versus tropical drivers.

The paper is fundamentally a study of how anthropogenic warming reorganises North Atlantic regimes and the NAO. Any link to Arctic amplification is contextual and mechanistic (via shared effects on the jet, gradients, and sea ice) rather than a direct focus of the analysis.

If you want, I can pull more specific NAO figures and results or discuss how these findings compare with other literature on Arctic amplification and the NAO.

Anthropogenic climate change leads to a pronounced reorganisation of wintertime North Atlantic atmospheric circulation regimes

Abstract

Regional climate variability manifests through distinct atmospheric regimes influencing weather, climate, and predictability. Yet their response to global warming remains unresolved. Using a hundred realisations from the Community Earth System Model Large Ensemble, we examine shifts in wintertime North Atlantic atmospheric regimes and the North Atlantic Oscillation before and after 1995, highlighting the detectable influence of anthropogenic warming on atmospheric circulation. The large- ensemble framework isolates internal variability by removing the ensemble mean. Under anthropogenic warming, the number of regime states associated with the forced response remains constant, although their spatial circulation patterns undergo substantial reorganisation. In contrast, internal variability alone exhibits a reduction in the number of regime states. Future projections indicate a shift toward more frequent positive phases of the North Atlantic Oscillation, accompanied by low-amplitude negative phases late in the century, alongside a marked decline in its variability and altered mid-tropospheric westerlies.

Core findings (from Results)

• Changepoint detection: The earliest clear anthropogenic signal in mid- tropospheric (500 hPa streamfunction) circulation appears around 1995 (in PC2 of the coupled SVD analysis). Analyses therefore contrast Pre-1995 (1850–1995) vs. post-1995 (1996- 2100).
• Full flow field (FF = forced and internal variability): Number of wintertime atmospheric regimes remains constant at four. Spatial patterns reorganise (northward shifts of cyclonic and anticyclonic centres; changes in intensity and phase- space distribution). Regime- to- regime transition probabilities weaken under warming, while persistence of certain regimes increases.
• Internal variability only (IV): Number of regimes decreases after 1995; one dominant (weaker-circulation) regime becomes more persistent and attracts more transitions.
• North Atlantic Oscillation (NAO): Forced response shows a modest but significant trend toward more positive phases through much of the 21st century, with a partial late- century reversal linked to increased low-amplitude negative events. Overall NAO variability declines. Mid- tropospheric westerlies strengthen in positive-NAO regimes and weaken in negative ones. CESM2-LE reproduces observed NAO characteristics reasonably well (within ensemble spread).

Methods snapshot

• Data: CESM2 Large Ensemble (100 members), monthly 500 hPa stream function and surface temperature (DJF), 1850- 2100, SSP3-7.0 scenario.
• Separation of forced response (ensemble mean) vs. internal variability.
• Coupled Singular Value Decomposition (SVD) between streamfunction and surface temperature (preferred over standard EOFs).
• Regime identification via clustering on leading PCs; Markov transition matrices for inter- regime dynamics.
• NAO index: standardised first PC of sea- level pressure.

The paper is open access. Code for figure reproduction is available on Zenodo, and the lead author has a “Behind the Paper” post on Springer Nature Communities.

Paper: Anthropogenic climate change leads to a pronounced reorganisation of wintertime North Atlantic atmospheric circulation regimes

Journal information: Communications Earth & Environment, volume 7, Article number: 155 (2026)

Published: 20 January 2026 (Version of record: 12 February 2026)

DOI: 10.1038/s43247-026-03180-0

Open access (PDF available on the page).

Authors: Susmit Subhransu Satpathy,
Christian L. E. Franzke,
Vincent Verjans &
Terence O’Kane