Mitigation Needed to Avoid Unprecedented Multi-Decadal North Atlantic Oscillation Magnitude
- Hakan Sener
- May 28
- 3 min read
Updated: 4 days ago
A 2025 study warns NAO extremes may triple by 2100, amplifying floods and storms—unless strong climate mitigation is pursued now.
A new study led by Doug M. Smith and colleagues from the Met Office Hadley Centre reveals that without strong emissions reductions, the North Atlantic Oscillation (NAO)—a key driver of weather patterns across Europe and North America—could reach unprecedented levels by the end of the century, resulting in increased flooding, storm damage, and economic loss.
The team applies a novel “emergent constraint” approach to improve NAO projections and correct for long-standing deficiencies in climate models, particularly those related to water vapour errors and atmospheric dynamics. Their findings challenge the conventional assumption that internal climate variability limits predictability, showing instead that the NAO may be far more sensitive to greenhouse gas forcing than models suggest.
Key Findings: The NAO and a Warming World
NAO Will Likely Intensify Without Mitigation
Under the high-emissions scenario (SSP5-8.5), the NAO could increase to 1.4–3.7 times its historical magnitude by 2100.
This intensification would push storm tracks northward, bringing more frequent and intense winter storms to northern and western Europe.
Climate Models Underestimate NAO Variability
Traditional models suffer from a “signal-to-noise paradox”, where model variability is greater than observed reality, leading to dampened projections.
Using the relationship between upper-atmosphere water vapour (the hygropause) and jet stream shifts, the authors correct this and greatly improve model accuracy.
Greenhouse Gases, Not Random Chaos, Are Driving the Shift
The study shows that GHG-induced tropical warming strengthens the meridional temperature gradient in the upper atmosphere, pushing the jet stream and NAO into a stronger, more positive phase.
Volcanic eruptions, by contrast, have historically weakened the gradient, reducing NAO magnitude—a contrast the models help capture.
Emergent Constraint: A Better Way to Model the Future
The authors developed an innovative approach using a metric based on the difference between the hygropause and jet stream latitudes to weight models. This allows for recalibrated projections that match historical trends more closely than raw ensemble averages.
When applied across a large ensemble of CMIP6 models, this constraint reveals a much greater NAO response to global warming than the models indicate on their own.
Implications for Europe and North America
A more positive NAO phase means warmer and wetter winters in northern Europe, and drier, colder conditions in southern Europe and the northeastern US.
This could exacerbate flooding risks, storm surges, infrastructure damage, and energy demand shifts across the Atlantic basin.
Importantly, the study finds that strong climate mitigation (SSP1-2.6) could significantly reduce these extremes—highlighting a narrow but actionable window to reduce impacts.
Ignoring Model Errors May Leave Us Unprepared
The study provides strong evidence that standard climate models may understate the risks posed by changes in atmospheric circulation. By correcting for key physical biases, this study reveals a future in which NAO-driven climate extremes could become more common and more damaging—unless global emissions are rapidly reduced.
The North Atlantic Oscillation is no longer just an academic curiosity—it is fast becoming a central factor in Europe and North America’s climate resilience strategy.
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