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.
USGS
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 most people, is regulated by how well mixed the ocean is in a given location. The more vertical mixing there is, the more cooler waters and nutrients stored in the deep oceans are then brought up to the ocean's surface. Those nutrients help feed the ocean's most basic and important forms of life like plankton. In short, less mixing equals less life.
Stronger storms are another result of warmer waters. So far this season, the Atlantic is a month ahead of a record pace with 23 named storms. While various factors have contributed to the overactive season, Mann says a warmer ocean is a big contributing factor.
Climate Central
Since 1900, Tropical Atlantic sea surface temperatures have warmed by an average of 2 degrees Fahrenheit, providing more high-octane fuel to storms.
This warmer water leads to more intense storms. A recent study conducted by NOAA's hurricane researcher Dr. Jim Kossin confirms that storms are getting stronger. Kossin told CBS News, "My message to your readers is globally, there's about a 25% greater chance now that a hurricane will be at major hurricane intensity than four decades ago. In the Atlantic there's about twice the chance."
Mann is also keen to focus on the impacts of a detrimental feedback on the carbon cycle. The increased near-surface warming and less downward mixing means that less of the carbon dioxide (CO2) can be absorbed and stored in the ocean. That's because physics dictates that warmer water holds less CO2, and also, less CO2 can be mixed downward. The result, Mann says, is that more CO2 accumulates in the atmosphere.
"It's unwise to be complacent given the accumulating scientific evidence that climate change and its impacts may well be in the upper end of the range that climate scientists currently project," said Mann. "There is ever-greater urgency when it comes to acting on climate."
But Mann emphasized that we still have time to act. However, he warns that the choice we make in this upcoming election may well determine whether we succeed or fail: "Our actions make a difference — something to keep in mind as we head into a presidential election whose climate implications are monumental."