There is compelling scientific evidence that climate change is causing significant changes in the world’s oceans. These changes are having a negative impact on marine ecosystems, including coral reefs, which are especially vulnerable to rising sea temperatures. Warmer water temperatures can cause coral bleaching, which is when coral loses its color and dies.
Furthermore, climate change is causing sea levels to rise, which can have a variety of negative consequences, including more frequent and severe coastal flooding, shoreline erosion, and saltwater intrusion into freshwater aquifers. These changes have the potential to have serious consequences for coastal communities and the species that rely on marine ecosystems. It is important that we take action to reduce our carbon emissions and mitigate the impacts of climate change on the world’s oceans.
Climate change will slow deep overturning ocean circulation in the coming centuries. Using three dozen Earth system models, researchers concluded that the Southern Meridional Overturning Circulation could completely shut down by 2300, wreaking havoc on the world’s marine ecosystems.
According to University of California, Irvine Earth system scientists, climate-driven heating of seawater is causing a slowdown in 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.
Analysis of the projections from 36 Earth system models over a range of climate scenarios shows that unchecked global warming could lead to a shutdown of the ocean deep circulation. This would be a climate disaster similar in magnitude to complete melting of the ice sheets on land.J. Keith Moore
In a recent study published in Nature Climate Change, these researchers analyzed projections from three dozen climate models and found that the Atlantic Meridional Overturning Circulation and the Southern Meridional Overturning Circulation will slow by as much as 42 percent by 2100. The simulations suggest that under worst-case warming, the SMOC could cease entirely by 2300.
“Analysis of the projections from 36 Earth system models over a range of climate scenarios shows that unchecked global warming could lead to a shutdown of the ocean deep circulation,” said co-author J. Keith Moore, UCI professor of Earth system science. “This would be a climate disaster similar in magnitude to complete melting of the ice sheets on land.”
The importance of overturning circulation
In the Atlantic, as warm water flows northwards on the surface, it cools and evaporates, making it saltier and denser. This heavier water sinks into the deep ocean and proceeds to the south where it eventually rises back up, carrying from the depths the nutrients that are the food foundation of marine ecosystems.
Furthermore, global ocean circulation creates a powerful factory for the processing of atmospheric CO2. Moore and his colleagues refer to the basic physical and chemical interaction of seawater and air as a “solubility pump,” which draws CO2 into the ocean. While ocean circulation returns some carbon to the atmosphere, the majority is sequestered in the ocean’s depths.
A “biological pump” also occurs when phytoplankton use CO2 during photosynthesis and the formation of carbonate shells. When plankton and larger animals die, they sink and slowly decompose, releasing carbon and nutrients deep in the ocean. Some is brought back up by circulation and upwelling, but some remains banked beneath the waves.
“A disruption in circulation would reduce ocean uptake of CO2 from the atmosphere, exacerbating and extending the hot climate conditions,” Moore explained. “The nutrients that support marine ecosystems would become increasingly trapped in the deep ocean over time, resulting in declining global-ocean biological productivity.”
According to Moore, humans rely on the solubility pump and the biological pump to help remove some of the CO2 emitted into the atmosphere by fossil fuel combustion, land use practices, and other activities.
“Our analysis also shows that reducing greenhouse gas emissions now can prevent the deep circulation from completely shutting down in the future,” he added.