A pivotal piece of research – published in the journal Nature Climate Change and produced with funding from the ASPECT program – has found that under high concentrations of greenhouse gases parts of northern Europe could face more severe flooding and increased storminess.
Context
Dr Doug Smith and a team of scientists from the Met Office found that under a scenario of very high concentrations of greenhouse gases by the end of the century, the North Atlantic Oscillation (NAO) will increase to levels never seen before. However, the authors stress that these impacts could be mitigated through efforts to reduce greenhouse gas emissions.
The NAO is the pressure difference between the Azores and Iceland. A strong pressure gradient drives the jet stream and the storm track further north and increases the strength of the westerly winds producing warm, wet and stormy winters in Northern Europe and cold, dry winters in southern Europe.
The team found that the NAO is influenced by climate change and volcanic eruptions. Volcanic eruptions cool the upper troposphere and tend to promote a negative NAO, whereas greenhouse gases have the opposite effect, warming the upper troposphere and promoting a positive NAO by shifting the winds polewards.
Key findings
- The study shows that some of the differences between model projections of the NAO are due to limitations of climatological water vapour in the models.
- The research reveals the NAO’s significant response to external forcings such as volcanic eruptions and greenhouse gases.
- The study also takes into account the ‘Signal to Noise Paradox’, which suggests that climate models may underestimate the magnitude of real-world NAO changes.
- The research results underscore the importance of mitigation efforts to avoid severe impacts from an unprecedented increase in the NAO.
- The study highlights the need for improved climate models to better predict future changes in the regional climate.
Implications
The researchers examined model differences in the simulations of the NAO in relation to atmospheric water vapour. Taking these differences into account, the team’s projections suggest that the NAO will increase to unprecedented levels which would have severe consequences for society in terms of increased flooding and storminess. The team also found that these impacts can be reduced or avoided by decreasing greenhouse gas emissions.
Water vapour is important in climate model simulations because it affects the troposphere and the stratosphere in different ways. In the troposphere it promotes warming, but in the stratosphere – where there’s very little water vapour – it promotes cooling because the radiation can escape freely to space. But, under the influence of increased concentrations of greenhouse gases, the troposphere warms and the stratosphere cools, creating a temperature gradient at around the tropopause level – around 200 hectopascal – which can shift the winds at that level, affecting the NAO.
The study also suggests that climate models may underestimate the magnitude of real-world NAO changes. The lead author said: “I think the most important consequence of this research is that taking models at face value potentially could leave society unprepared for impending extremes. And that’s for two reasons. One, because the models are completely different in terms of their simulations of atmospheric circulation, and two, because they tend to underestimate changes in atmospheric circulation.”
Reference: Smith, D.M., Dunstone, N.J., Eade, R. et al. Mitigation needed to avoid unprecedented multi-decadal North Atlantic Oscillation magnitude. Nat. Clim. Chang.15, 403–410 (2025). https://doi.org/10.1038/s41558-025-02277-2
