A change in the natural wind system over the Atlantic Ocean due to worsening climate change could lead to increasingly severe winter flooding and storm damage in northwestern Europe, scientists have said.
They found changes to the “North Atlantic oscillation” (NAO) could increase the frequency of cold snaps, floods and storms, and believe the threat is being underestimated due to limitations in current climate models.
The study, led by climate scientists at UK Met Office, concludes that changes to NAO – which normally provides a temporary cooling and warming over this part of the world – may have been underestimated and the region is not sufficiently prepared for future impacts.
The NAO is described as “a large-scale atmospheric pressure see-saw” and is a key driver of winter weather patterns in Ireland, the UK, western Europe and the eastern US. It is measured by the gradient between high pressure over the Azores and low pressure over Iceland and controls the strength of the prevailing winds.
How a hotter world is affecting Ireland in five graphics
Winter flood and storm damage may worsen due to Atlantic wind system changes, scientists warn
Dublin company behind glow-in-the-dark road markings that could be a lifesaver
Ireland must scale up preparations for extreme weather events, climate council warns
This NAO is different from the Atlantic meridional overturning circulation (Amoc), an ocean current that is weakening amid concerns it will collapse and give Ireland a much harsher climate due to global warming.
The Amoc is a marine conveyor belt that carries heat, carbon and nutrients from the tropics towards the Arctic Circle, where it cools and sinks into the deep ocean. This churning helps to distribute energy around Earth and modulates the impact of human-caused global heating.
Irish climatologist Prof John Sweeney said the oscillation is in effect a measure of “westerliness” in terms of wind patterns affecting Ireland.
The normal pattern is cyclical, where the wind system varies throughout the year. It is greatly influenced, he said, by the natural warming phenomenon known as the El Niño in the Pacific Ocean, which has a major influence on global weather.
But in the event of global warming, changes to the oscillation are inevitable. “They are to be expected if the warmth of the ocean [including the Atlantic] increases,” he added.
Errors in current models predicting climate scenarios have led to uncertainty in predictions of the NAO’s future behaviour, the scientists conclude.
“Taking account of these errors reveals that the NAO could be disastrous for this part of the world, which is seriously underprepared,” they say.
The study raises concern about how water vapour in the atmosphere is represented, leading to uncertainty in predictions of the NAO’s future behaviour. Taking account of these limitations “reveals a substantial response of the NAO to a combination of volcanic eruptions and greenhouse gases” due to climate change.
The findings indicate under a scenario of very high concentrations of greenhouse gases by 2100, the NAO will increase to levels never before seen, posing severe risks from extreme weather, notably flooding and storm damage. However, they say these impacts could be countered through efforts to reduce carbon emissions.
“These findings have major implications for understanding and preparing for extreme weather events. Our study suggests that taking model projections at face value could leave society unprepared for impending extremes,” said the study’s lead author Dr Doug Smith.
“Mitigation efforts [cutting emissions] are crucial to prevent the severe impacts associated with an unprecedented increase in the NAO,” he said.
The study highlights the need for improved climate models to better predict future changes “in the regional climate”.
