Climate change is producing amnesia in the oceans

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Loss of 'ocean memory' means tomorrow's ocean temperature will likely look a lot like today

most of the oceans
are constantly losing their memory year year after year due to global warming, reveal state-of-the-art projections from Earth System Models.

Compared to the atmosphere's rapid climate fluctuations, the slowly varying ocean exhibits strong persistence, or "memory," meaning that tomorrow's ocean temperature will likely look much like today, with only slight changes. As a result, ocean memory is often used to predict ocean conditions, says the study, published in Science Advances.

The decrease in oceanic memory is found as a collective response through
heClimate models to human-induced warming. As greenhouse gas concentrations continue to rise, such memory decline will become increasingly apparent.

"We discovered this phenomenon by examining the similarity in ocean surface temperature from one year to the next. as a simple metric for ocean memory," said Hui Shi, lead author and a researcher at the Farallon Institute in Petaluma, California. »It's almost as if the ocean is developing amnesia«.

It is found that the memory of the ocean is related to
the thickness of the upper layer of the ocean, known as mixed layer. The deeper mixed layers have a higher heat content, which confers more thermal inertia which translates into memory. However, the mixed layer over most oceans will become shallower in response to continued anthropogenic warming, resulting in decreased ocean memory.

“Other processes, such as changes in ocean currents and changes in energy exchange between the atmosphere and the oceanalso contribute to changes in ocean memory, but increased mixed layer depth and resulting decreased memory occur in all regions of the world, making it a factor.
important to consider for future climate predictions», said Robert Jnglin Wills, a research scientist at the University of Washington in Seattle, Washington, and a co-author of the research.

Along with the decreased memory of the ocean, it is also found that
the thinning mixed layer increases random fluctuations in sea surface temperature. As a result, although the ocean will not become much more variable from year to year in the future, the fraction of signals useful for prediction is greatly reduced.

“Reduced ocean memory coupled with increased random fluctuations suggest
intrinsic changes andn the system and new challenges in forecasting under warming," said Fei-Fei Jin, a professor of atmospheric sciences at the University of Hawai'i in the Manoa School of Ocean and Earth Sciences and Technology, and co-author of the research. .

The memory loss of the oceans not only affects the prediction of physical variables, but could also
influence the way we manage sensitive marine ecosystems.

Less time to forecast the tides

“Reduced memory means
less time in advance to make a forecast. This could hamper our ability to predict and prepare for changes in the oceans, including marine heat waves, which are known to cause sudden and pronounced changes in ocean ecosystems around the world," he said. Michael Jacox, a NOAA research scientist, and co-author of the research.

In fisheries management, biological parameters used for stock assessment are estimated assuming a stable environment represented by the recent past.
Reduced ocean memory may make such an estimate inaccurate and calls for new approaches in ecosystem-based fisheries management to include real-time ocean monitoring and other such efforts.

It is likely that the decrease in oceanic memory also exerts
impacts on populations of biological resources. Depending on whether species are adapted to constant or more variable environmental conditions, future changes in their population can be better estimated and predicted by taking oceanic memory loss into account.

In addition to ocean prediction, prediction of land-based impacts on temperature, precipitation, and extreme events could also be affected by ocean memory decline due to its reliance on persistent sea surface temperature as a source. of predictability.

As the memory of the ocean continues to decline, researchers are likely to be challenged to search for alternative predictors for skillful predictions.

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