Review of the climate change impacts on ocean circulation relevant to the UK and Ireland

A review from the Marine Climate Change Impacts Partnership (MCCIP) highlights concerns over changes in ocean circulation systems critical to the UK and Ireland’s climate. NCAS, NOC and Met Office researchers contributed to the study focusing on the Atlantic Meridional Overturning Circulation (AMOC), a vast system of currents that regulates heat and carbon distribution across the globe.

Current Trends

The AMOC has shown fluctuations over recent decades—strengthening in the 1990s, weakening through the early 2010s, and a brief recovery before returning to decline in recent years. While long-term trends remain uncertain due to sparse data, recent observations confirm a weakening. Freshwater influx from melting Arctic and Greenland ice could be influencing the subpolar North Atlantic. Currently, the Arctic is warming about twice as fast as the rest of the planet contributing to an enhanced ice loss from Greenland and Arctic glaciers. The resulting increase in freshwater flows could have a larger impact on the AMOC in the future.

Future Outlook

Climate models consistently project further weakening of the AMOC by 2100, at a rate similar to the observed decline of approximately one Sverdrup per decade since 2004. Whilst there have been an increased number of studies warning of a potential tipping point in the AMOC in this century, there are still large uncertainties about the robustness of the underlying data and measures being used to assess this. Changes in shelf sea circulation—affecting fisheries, sediment transport, and biodiversity—are also expected, but predictions are less certain.

Studies have confirmed that a weakened AMOC could

• increase the strength of the jet stream, reducing atmospheric blocking and the duration of cold spells over Ireland and Southern UK,
• lead to a decrease in annual mean precipitation over the UK, however, this signal varies seasonally,
• impact storm tracks through changing North Atlantic sea surface temperature gradients,
• affect sea level extremes directly through sea surface height and indirectly through storm surges, a major contributor to coastal flooding in the UK, due to changes in the North Atlantic storm track, impact the marine ecosystem, where it can influence biogeographic shifts through different mechanisms.

Key Challenges

Reconciling observational data with climate models remains a critical challenge to providing confidence in future projections. Projections consistently show a weakening of the AMOC in the future, but concern exists about whether current models could overlook the possibility of an AMOC collapse. Further research is required to understand the timescales for when impacts occur following an AMOC decline.

Projections of shelf sea circulation and exchange in future climates should be improved through model development as well as validation with observations. Researchers also stress the need for sustained monitoring, particularly in shelf seas, where local impacts could be felt sooner and more sharply.

The report underscores that ocean circulation changes are not just a scientific concern—they carry profound implications for marine ecosystems, coastal economies, and global climate stability.

For the full report, visit MCCIP Ocean Circulation Update.