Michael Mann: Ocean Stratification Is Not Good News. Very Not Good News.

[hatrack]

EDIT

My colleagues and I have just published an article in the journal Nature Climate Changeshowing that the oceans are not only becoming more stable, but are doing so faster than was previously thought. Led by Guancheng Li of the Institute of Atmospheric Physics in China, our team (which also includes Lijing Cheng, Jiang Zhu, Kevin Trenberth and John P. Abraham) analyzed a quantitative measure of stability known as “stratification”. We found that the stratification of the world oceans is not only increasing, but is doing so at a greater rate than estimated in previous studies. Our study uses more comprehensive data and a more sophisticated method for estimating stratification changes, and we found a nearly 6 percent increase in the stratification of the upper 200 meters (~650 feet) of the world oceans over the past half century.

This seemingly technical finding has profound and troubling implications. The more stable the upper ocean, the less vertical mixing that takes place. This mixing is a primary means by which the ocean buries warming surface waters. So the surface warms up even faster. It’s what we call a “positive feedback”—a vicious cycle. That’s bad for a number of reasons. As we currently watch the most active Atlantic hurricane season on record play out, a key underlying factor is the anomalous surface warmth of the tropical Atlantic. The increasingly intense and damaging hurricanes we’ve seen in recent years have fed off warmer surface waters. More stably stratified waters tend to inhibit the wind-driven mixing up of cold deeper waters that often serves as a sort of release-valve, shutting off the source of energy at the surface that intensifies these storms. A more stably stratified ocean potentially favors more intense, destructive hurricanes.

Warmer waters absorb less atmospheric carbon dioxide (just as warm soda loses its carbonation faster when you open the top.) Less ocean mixing also means that less of the atmospheric carbon dioxide gets buried beneath the ocean surface. So carbon pollution accumulates even faster in the atmosphere, causing yet more warming. Another “positive (i.e. bad) feedback” and another double whammy. Finally, warmer upper ocean waters hold less dissolved oxygen. And less ocean mixing means less oxygen (and nutrients,) since oxygen and nutrients depleted by sea life are less likely to be replaced from rising, colder more oxygen-rich waters. That’s bad for marine productivity. It means the potentially interruption of food webs and fish populations that provide the main source of protein for more than three billion people.

Our findings also have important implications for how much additional warming we may see in the future. State-of-the-art climate models used today to predict future climate change tend to underestimate the stratification of the ocean. They consequently bury heat (and carbon) too easily beneath the ocean surface. For that reason, they are likely underestimating the impact that the increased stratification (and decreased mixing) found in our study is having on rising atmospheric carbon dioxide levels and surface warming.

EDIT

https://climatecrocks.com/2020/09/28/ocean-stratification-is-not-good-news-very-not-good/

[bronxiteforever]

1. Kick and recommend.