Among scientists a noticeable shift in major ocean currents is emerging, with concerns rising about their potential collapse. Warming seawater driven by human-ca influences is slowing deep circulation in the Atlantic and Southern Oceans. If this trend continues, the ocean’s capacity to remove carbon dioxide from the atmosphere could be severely reduced, amplifying global warming according to Earth system researchers at the University of California, Irvine.
In a recent Nature Climate Change study the researchers examined projections from three dozen climate models and found that the Atlantic Meridional Circulation and the Southern Meridional Circulation are likely to slow by about 42 percent by 2100. In the most pessimistic scenarios, these currents could shift toward a near collapse by 2300. In the study, projections from 36 Earth system models across a range of climate futures were analyzed to assess how sustained warming might disrupt deep ocean circulation. These findings underscore the potential for a climate crisis comparable in scale to the complete melting of large ice sheets, according to J. Keith Moore, a co author and professor of Earth Systems Sciences at UCI.
Big currents seem to be on their way to collapse.
In the Atlantic, surface currents transport warm water northward where it evaporates and becomes saltier. This makes the water denser, causing it to sink and travel southward, a cycle that supports nutrient transport from the deep ocean to surface waters and sustains marine ecosystems.
A planet wide ocean circulation acts like a global factory for processing atmospheric carbon dioxide. The basic physics and chemistry of seawater and air drive a solubility pump that pulls CO2 into the ocean. While some carbon returns to the atmosphere through circulation, a large portion remains stored in the ocean depths.
Formation of carbonate crusts
Another crucial process involves phytoplankton using CO2 during photosynthesis and contributing to the formation of carbonate structures. When plankton and larger marine life die, their remains sink through the water column, slowly breaking down and releasing carbon and nutrients deep in the ocean. Some of this material is brought back to the surface by circulation and upwelling, while another portion remains locked within subsurface layers for longer periods.
Moore notes that impairment of circulation would reduce the ocean’s uptake of atmospheric carbon dioxide and could intensify hot weather conditions over extended periods. This connection highlights the intertwined fate of climate and marine systems, where a slowdown of deep ocean currents may amplify extreme heat and disrupt regional climate patterns.
Impacts on climate and biodiversity could be substantial. Over time, vital foods for marine ecosystems become increasingly trapped in deeper waters, reducing the global ocean’s biological productivity and altering ecosystem balance. Human activities, including burning fossil fuels and land use changes, contribute to the increases in atmospheric greenhouse gases that drive these changes. A reduction in emissions now might prevent the complete disruption of deep circulation in the future, reducing the risk of a profound climate disruption, according to Moore.
The study consolidates evidence that ongoing warming could threaten the deep ocean’s role in stabilizing climate. By altering how heat and carbon are distributed across ocean basins, these changes would influence weather extremes, precipitation patterns, and the health of marine habitats worldwide. The research emphasizes the need for robust climate action to protect ocean health and global climate stability.
Researchers reference the detailed findings published in Nature Climate Change and encourage ongoing evaluation of climate model projections to better understand potential trajectories for ocean circulation under various emission scenarios.