When you think of the changing climate, the first thing that likely comes to mind is extreme weather swirling about in the atmosphere. But focus on the oceans — they ultimately control our climate destiny.
The oceans contain 268 times the amount of mass of the atmosphere and can store 1,000 times more heat. The oceans absorb the heat equivalent of 5 Hiroshima style atomic bombs per second, more than 90% of climate change’s excess global heating.
As a result of this excess heat, the oceans are becoming significantly more “stratified,” according to a new study published Monday by some of the world’s top climate scientists. In other words, like olive oil and water in a glass, the oceans are not mixing as well as they used to and that has significant ramifications for many important Earth system functions.
The new data shows that the ocean has become more stratified by 5.3% since 1960 for the upper 2,000 meters. An even stronger ocean stratification increase — as much as 18% — has been observed in the upper 150 meters.
Stratification means less mixing, which leads to more heat in the surface waters. That increases energy available for storms and impacts life in shallow waters.
“Once again, the observations are showing key climate change impacts playing out faster and more dramatically than the models have predicted,” said a co-author of the study, Michael Mann, distinguished professor of atmospheric science at Penn State. “In the case at hand, the models are underestimating the increase in ocean stratification that we find in the observations. That means they are potentially underestimating a whole range of critical climate change impacts.”
The warmer — thus lighter — the water is, the less able it is to sink. However, sinking and rising water is necessary for the oceans to fulfill basic functions from regulating climate to supporting life in the oceans.
Below is a simplified visual of the Great Ocean Conveyor Belt showing how interconnected the far reaches of the ocean are, with blue arrows indicating cold, deeper waters, red arrows noting warm, shallower waters and the transition between illustrating where waters sink or ascend.
When the oceans are more stratified, warm water builds up near the surface, with less heat escaping down into the deep ocean. This is one of the mechanisms leading to more marine heatwaves, a phenomena that is catastrophic for ecosystems like coral reefs, 50% of which have already been wiped out. And because of future heating, the remaining reefs may all be gone by late this century. In the past 100 years, there has been a greater than 50% increase in annual marine heatwave days globally.
It’s not just coral reefs impacted from less mixing and more surface warming. Much of what is called ocean “primary productivity” by scientists, better known simply as ‘life’ to…