A Major Ocean Current Is On The Verge of Collapse. Scientists Say The Effects May Reach California
The Atlantic Meridional Overturning Circulation (AMOC) is a crucial component of Earth's climate system, acting as a planetary conveyor belt that brings balmy water northward from the tropics to Europe and then cycles the cooled water back south along the seafloor. However, human-caused climate change is slowing this vital system and even threatening a potential near-future collapse.
A recent study published in Nature Communications, led by Mohima Mimi from the University of California, Riverside, has shed new light on the potential consequences of an AMOC collapse. The research utilizes decades of NASA-acquired atmospheric data and climate simulations to project the evolution of the AMOC, revealing significant climatic differences worldwide.
One of the key findings is that a weakening AMOC will strengthen storms across parts of North America, particularly along the California coast, while reducing them over Greenland and the Arctic. This is due to the AMOC's influence on atmospheric rivers (ARs), which are long, narrow strips of concentrated water vapor in the atmosphere. Strong ARs can carry up to 15 times more water than the Mississippi River's flow.
In California, ARs play a dual role. They provide up to 50% of annual rainfall, especially in the western US, and are the main driver of the state's volatile water supply. However, they also increase flood risk, as they frequently generate floods, even during droughts, endangering lives, destroying infrastructure, and impacting water quality.
The study also highlights the global implications of an AMOC collapse. Over Antarctica, ARs contribute to 40-80% of summer meltwater in West Antarctic ice shelves, threatening ice stability and accelerating global sea level rise. Furthermore, the global mean frequency of ARs may increase by around 50%, with more moisture and longer durations, as the high-altitude westerly jet stream shifts toward the poles due to anthropogenic warming.
As the AMOC slows, it will alter oceanic temperatures and decrease atmospheric moisture in the Northern Hemisphere, while increasing it in the Southern Hemisphere. This will lead to more frequent and intense ARs in certain regions, such as South America's east coast, southern Asia, western Europe, parts of the Pacific, and around Antarctica. The greatest increases are expected along North America's west coast, from Baja California to Alaska.
Conversely, ARs may become less frequent across the Arctic, Greenland, and northern Asia, as a weakened AMOC leads to cooler surface air temperatures and reduced moisture content. Other lower-latitude areas, including northern Australia and the South Pacific, may also experience a decrease in AR frequency.
The study emphasizes the interconnectedness of Earth's climate systems. A change in the AMOC can have far-reaching effects, driving storms across America, intensifying Amazonian rainfall, and displacing tropical rain belts southward. Mimi highlights the importance of understanding these connections to better prepare for future changes in water resources and extreme weather.
While the research provides valuable insights, it also underscores the need for further exploration and adaptation strategies. The sometimes-destructive ARs also present opportunities, such as California's potential to capture more water by restoring natural landscapes to mitigate droughts caused by hotter, drier weather. Additionally, the study reminds us of the irreversible interdependence of our planet's processes, where a single major ocean current can have profound global impacts.
