According to the University of California, Irvine Earth system scientists, climate-driven heating of seawater is slowing deep circulation patterns in the Atlantic and Southern oceans, and if this process continues, the ocean's ability to remove carbon dioxide from the atmosphere will be severely limited, exacerbating global warming.
The importance of overturning circulation
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In a recent study published in Nature Climate Change, these researchers examined forecasts from three dozen climate models and discovered that the Atlantic and Southern Meridional Overturning Circulations will slow by up to 42 percent by 2100. The calculations indicate that, in the worst-case scenario, the SMOC might end totally by 2300.
"Analysis of forecasts from 36 Earth system models across a variety of climatic scenarios suggests that unchecked global warming might result in the shutdown of ocean deep circulation," co-author J. Keith Moore a UCI Earth system science professor. "This would be a climatic calamity on par with the entire melting of the land ice sheets."
As warm water moves northward over the surface of the Atlantic, it cools and evaporates, becoming saltier and denser, as per ScienceDaily.
This heavier water dips into the deep ocean and travels south, ultimately rising again, delivering nutrients from the depths that constitute the food base of marine life.
Furthermore, global ocean circulation generates a strong factory for the processing of atmospheric CO2.
Moore and his colleagues refer to the underlying physical and chemical interaction of salt water and air as a "solubility pump," which sucks CO2 into the ocean.
While ocean circulation returns some carbon to the atmosphere, the majority is trapped in the ocean's depths.
A "biological pump" also occurs when phytoplankton utilizes CO2 during photosynthesis and the formation of carbonate shells.
When plankton and bigger creatures die, they sink and slowly decompose, releasing carbon and nutrients deep in the ocean.
Some are brought back up by circulation and upwelling, but some remains banked beneath the waves.
According to Moore, a disturbance in circulation would diminish ocean absorption of CO2 from the atmosphere, increasing and extending the hot climatic conditions.
The nutrients that support marine ecosystems would become more locked in the deep ocean over time, resulting in decreased global-ocean biological output.
How is climate change impacting the world's oceans?
Rising temperatures raise the possibility of permanent loss of marine and coastal ecosystems.
Widespread effects have been documented, including coral reef and mangrove damage and species migration to higher latitudes and elevations where the water may be cooler.
According to the latest UN Educational, Scientific, and Cultural Organization projections, more than half of the world's marine species may be on the verge of extinction by 2100.
With today's 1.1°C temperature increase, an estimated 60% of the world's marine ecosystems have already been destroyed or are being utilized in an unsustainable manner.
A 1.5°C increase threatens to kill 70 to 90% of coral reefs, whereas a 2°C increase means a virtually 100% loss at the point of no return.
Marine heatwaves have increased in frequency, becoming longer-lasting, more severe, and more widespread.
According to the IPCC, human activity is the primary cause of the observed rise in ocean heat since the 1970s.
Between 2006 and 2015, the bulk of heatwaves occurred, resulting in significant coral bleaching and reef destruction.
Nearly 60% of the world's ocean surface suffered at least one session of marine heatwaves in 2021.
According to the UN Environment Programme, if the ocean continues to warm, all of the world's coral reefs would bleach by the end of the century.
Coral bleaching happens when reefs are stressed and lose their life-sustaining tiny algae.
