(CN) — The world's oceans hit their highest temperatures in recorded history, according to a study published in the journal Advances in Atmospheric Science on Wednesday.
For the study, 24 scientists across 16 institutions worldwide analyzed observations of ocean heat content and its impact dating back to the 1950s. They found that changes in Earth’s ocean heat content, salinity and stratification — the separation of water into layers — provide vital indicators for changes in heat distribution and the hydrological cycle.
“First of all, the oceans hold the key to the climate. The oceans are what absorb almost all of global warming heat. So, if you want to know how fast the Earth is warming, the answer is in the oceans. If you want to know what our future climate is going to look like, the answer is in the oceans,” said John Abraham, study co-writer and professor of mechanical engineering at St. Thomas University.
Abraham said the research took millions of temperature measurements of ocean water surfaces to depths of over 6,500 feet. From there, researchers determined how much the oceans have heated up since 1958.
“We were able to show that, between 1958 and about 1980, the warming was pretty modest,” Abraham said. “It was a slow but steady increase. And then between about 1980 and the year 2000, the oceans began to warm up much more dramatically.”
In 2022 alone, researchers found Earth’s oceans exceeded the 2021 record by 10 zettajoules — a joule with 21 zeros behind it — and among the world’s seven oceanic regions, the North Pacific, North Atlantic, Mediterranean Sea and Southern Ocean recorded their highest ocean heat content since the 1950s.
According to lead researcher Lijing Cheng from the International Center for Climate and Environmental Sciences, more than 90% of the excess heat accumulated by Earth’s climate system is deposited into its oceans. However, Cheng writes that “rising ocean temperatures bolster the energy exchanges from ocean to atmosphere, increase the quantity of atmospheric moisture and change the patterns of precipitation and temperature globally.”
Added to the issue of salinity, and now we’re talking about a problem of ocean circulation.
“The changes in ocean salinity reflect the global exchanges of surface freshwater,” Cheng writes. “Evaporation refers to the transfer of freshwater from a water body to the atmosphere, leaving behind liquid water that is higher in salinity. On the other hand, precipitation injects freshwater into otherwise saline water, resulting in freshening.”
In short, as the climate becomes warmer, salty water becomes saltier, and freshwater becomes fresher. According to researchers, the “salty-gets saltier” pattern reached its highest level on record in 2022, and with that comes issues of ocean stratification.
“We don't like stratified oceans. The reason why we don't like them is when the oceans become very stratified or stable, they don't move,” Abraham said. “You'll get waters that sit near the surface for a long time, and they will get hot because they get sunlight, and they will absorb a lot of carbon dioxide from the atmosphere.”
Under normal circumstances, hot, carbonated water at the ocean surface falls to the bottom of the ocean. “But they're not doing that as much anymore,” Abraham said.
“At some point, they'll get saturated, and they will no longer be able to take in more heat or carbon dioxide. So, when the ocean becomes stratified, it actually makes it harder for the oceans to soak up the heat and carbon dioxide that we are pumping into the atmosphere.”
Researchers also noted how this imbalance in the ocean can lead to climate patterns where rainy climates experience more rain and drier climate become drier.
“Some places are experiencing more droughts, which lead to an increased risk of wildfires, and other places are experiencing massive floods from heavy rainfall, often supported by increased evaporation from warm oceans,” said Kevin Trenberth, co-author and researcher at the National Center for Atmospheric Research and the University of Auckland, in a statement. “This contributes to changes in the hydrologic cycle and emphasizes the interactive role that oceans play.”
But while the researchers may seem like the bearers of bad news, Abraham is quick to point out that humanity has options.
“We humans can reduce emissions, and we can start taking action to reduce global warming,” Abraham said. “We have the technology available right now. We just, in some respects, lack the will to institute good policies.”
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