What’s behind our shifting weather patterns? Study identifies key causes of ocean circulation change

Pattern of ocean currents may be responsible for warmer weather in north-west Europe. By Conrad Duncan

The UK has enjoyed a wave of hot weather in recent days, with meteorologists recording three successive warmest days of the year this week (PA)

Researchers have identified the key factors that influence a vital pattern of ocean currents which many scientists believe brings warmer than usual weather to the UK.

The Atlantic meridional overturning circulation (AMOC), which carries warm water from the tropics northwards, is thought to be responsible for warmer temperatures in north-west Europe.

However, climate models have suggested that the AMOC is likely to weaken over the coming decades, presenting widespread implications for the regional and global climate.

A new study, led by scientists from the University of Exeter and the University of Oxford, has found that winds are a “key factor” in monthly and annual AMOC variation.

“Understanding AMOC variability is challenging because the circulation is influenced by multiple factors that all vary and whose overlapping impacts persist for years,” lead author Dr Yavor Kostov, from the Department of Geography at the University of Exeter, said.

“Our findings reveal the vital role of winds in driving changes in this ocean circulation. Winds were a key factor both in the sub-tropical and sub-polar locations we examined.”

Dr Kostov added that scientists should focus on monitoring these winds as the climate changes, with particular attention paid to “key regions on continental boundaries and the eastern coast of Greenland”.

The research was put together by collecting observational data from large arrays of monitoring equipment, such as tools off the coasts of Florida and Africa, and in the North Atlantic between Greenland and Scotland, run by the international RAPID and OSNAP projects.

It showed that there was a different picture for the causes of variation at two key locations, with AMOC variability off the southern US dominated by the impact of winds and variability in the North Atlantic generated by the combined effects of winds, heat and freshwater anomalies.

“Our reconstruction suggests that, compared to the subtropics, the overturning circulation in the subpolar North Atlantic is more sensitive to changes in the background ocean state, such as shifts in the sites of deep convection,” Dr Kostov said.

“This implies that future climate change may alter annual AMOC variability in this region. It emphasises the need for continued observations of the subpolar North Atlantic ocean.”

The study, which has been published in the journal Nature Geoscience, also found that changes in the surface temperature and salinity (saltiness) of water near Canada and Greenland could trigger a delayed remote impact on the Atlantic circulation as far south as Florida.

The research was funded through the UK Natural Environment Research Council, as well as the National Science Foundation, National Oceanic and Atmospheric Administration, NASA and Simons Foundation in the US.