Observed changes and coherence in the Gulf Stream system

The steady supply of warm Gulf Stream water to subpolar latitudes is crucial for maintaining a mild, maritime climate in north-western Europe. Ongoing anthropogenic climate change has prompted the oceanographic community to ask whether a slowdown of the North Atlantic circulation has occurred as a response to changes in heat and freshwater fluxes. The question has also caught the attention of policy makers and the media. However, climate models, ocean transport measurements, and paleo and proxy reconstructions show large discrepancies regarding the ‘state’ of the North Atlantic circulation over the historical period. Here, we use available measurements of North Atlantic and Nordic Seas circulation strength to discuss and reflect on potential circulation slowdown. The measurements indicate a stable circulation, but the short record makes distinguishing potential long-term trends from interannual and decadal variability difficult. The sensitivity seen in literature to methodology, data type, region, and time period over which trends are evaluated, demonstrates the lack of robust evidence for a circulation slowdown. The findings warrant caution and nuance in terms of interpreting and communicating research on past and future changes in North Atlantic circulation strength.