The Ocean Can Remember for 20 Years, Study Says
To create accurate climate models, scientists need to understand how long conditions persist in the ocean.
A new study led by scientists from the University of Liverpool analyzed the “memory” of the North Atlantic and created a new framework for understanding ocean memory.
They discovered that temperature fluctuations persist for a full 10 to 20 years, which is much longer than current models predict.
Memory can be a flighty thing. The past can be recalled with rose-colored glasses, and many of our memories dim as we age—there’s a reason eyewitness testimony is considered one of the most unreliable forms of evidence in a judicial proceeding. However, the ocean doesn’t have these same failings when it comes to memory. While this doesn’t indicate some form of neurological oceanic hive mind, this aquatic form of memory refers to the ability of oceans to retain certain ecological conditions. Climate scientists are eager to understand the “strength” of this memory, as an inaccurate representation could throw off current models and predictions for the future as the world warms.
However, determining ocean memory isn’t easy, as the continual alteration of atmospheric forcing—how changes in the atmosphere impact land and sea modeling—masks the more long-term effects of ocean circulation. To help clear up this oceanic misunderstanding, scientists from the University of Liverpool set out to answer a simple question: “How long does the ocean remember?” The results, which were published earlier this year in the journal Geophysical Research Letters, indicate that the North Atlantic’s memory lasts anywhere for one to two decades, which is far longer than current estimates of only a handful of years.
“The study addresses a fundamental question of what ocean memory truly is,” University of Liverpool’s Hemant Khatri, a lead author of the study, said in a press statement. “The new ocean memory framework reveals physical mechanisms responsible for multi-year ocean memory and paves the way for new methods for evaluating climate models.”
The study focused on how the North Atlantic Oscillation influences subpolar North Atlantic Ocean temperatures. This new “ocean memory framework” accounted for short-term local effects involving air-sea heat fluxes, as well as long-term impacts created by ocean circulation. These long term effects include gyre circulations—the largest systems of rotating ocean currents—and meridional overturning, such as the Atlantic Meridional Overturning Circulation (AMOC) that brings warm water north and cool water south (and has been slowing in intensity since the 90s). The results of the team’s various models showed that temperature anomalies in the ocean persisted for a full 10 to 20 years before fully dissipating, though the team notes that variability can occur from region to region due to differences in background circulation and basin size.
“Ocean memory in the subpolar North Atlantic is estimated to be approximately 18 years based on observations, while climate models suggest a range of 8–12 years,” the authors wrote. “The significant discrepancy between ocean memory in observations and climate models suggests that climate models may be too dissipative in terms of ocean memory…potentially underestimating multi-decadal climate variability.”
This underestimation of nature’s memory only highlights the existential need to lower emissions. The World Economic Forum reported in 2022 that if the world magically went to zero emissions overnight, there’d still be a 42 percent change in temperatures, exceeding safe limits. Because of this memory, it’s vital that humans end this self-inflicting greenhouse trauma as soon as possible, so that the healing—and the forgetting—can begin.
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