Climate researchers find that the North Atlantic has a memory of almost two decades

A research team led by the University of Liverpool has found that the North Atlantic has a memory of around one to two decades, significantly exceeding previous estimates of a few years.

Ocean memory refers to the persistence of ocean conditions and is an important source of predictability in the climate system across weather timescales. However, the fundamental question: “How long does the ocean remember?” was unclear. The difficulty in identifying ocean memory is due to the continuous changes in atmospheric forcing, which obscure the longer-term effects of ocean circulation.

Reported in an article published in the magazine Geophysical Research LettersThe research team was able to quantify ocean memory by tracking the evolution of ocean temperatures in response to a single extreme atmospheric event. The authors note that there are fast and slow responses, involving an immediate atmospheric effect on surface temperature and a delayed redistribution of heat in the ocean.

The authors attribute the North Atlantic’s expanded memory to slow changes in ocean circulation and heat transport.

Their results suggest that fluctuations in ocean temperatures over a decade have a significant impact on regional climate, such as air temperatures.

It also provides support that careful analyzes of observations can improve future climate projections over a decade.

Dr. Hemant Khatri, from the University of Liverpool’s School of Environmental Sciences and lead author of the study, said: “The study addresses a fundamental question about what ocean memory really is. The new ocean memory framework reveals physical mechanisms responsible for multi-year memory of the oceans and paves the way for new methods for assessing climate models.

Professor Ric Williams, also from the University of Liverpool and co-author of the paper, said: “This is the first time we have been able to measure ocean memory. We find that, in contrast to observation-based estimates, state-of-the-art climate models significantly underestimate ocean memory, estimating it to be only eight to ten years. This significant discrepancy in ocean memory could have significant implications for the accuracy of decadal climate predictions from these models.

“Our work shows how the ocean impacts our climate and how understanding ocean temperature changes will lead to better climate projection skills over the next decade.”