Atlantic Ocean current collapse could trigger severe California storms

Atlantic Ocean current collapse could trigger severe California storms

A critical system of Atlantic Ocean currents is significantly more likely to collapse than previously estimated, according to recent research. The Atlantic Meridional Overturning Circulation (AMOC), which functions as a planetary conveyor belt moving warm tropical water toward the Northern Hemisphere, is showing signs of a potential breakdown that could trigger catastrophic weather shifts across the Americas, Europe, and Africa.

New findings published in Science Advances indicate the AMOC is projected to slow by an estimated 42% to 58% by 2100. This projection is approximately 60% higher than the average of previous standard climate models. Researchers used a mathematical technique called ridge-regularized linear regression to combine real-world ocean observations with simulations. According to lead author Dr. Valentin Portmann of the Inria Centre de recherche Bordeaux Sud-Ouest, the AMOC is closer to a tipping point than previously thought.

Global Climatic Ripple Effects

While the current is located in the Atlantic, its influence extends globally. A study published in Nature Communications reveals that a weakening AMOC alters oceanic temperatures and atmospheric moisture, which in turn affects "atmospheric rivers"—long, narrow strips of concentrated water vapor.

Mohima Mimi, a climate dynamics researcher at the University of California, Riverside, explains that a weakening AMOC will strengthen storms across parts of North America by the end of the century, specifically along the California coast. In California, these atmospheric rivers are described as a double-edged sword; they provide up to 50% of annual rainfall in the western US but also generate floods that threaten infrastructure and water quality.

The impacts extend to the poles and other continents:

• The Arctic and Greenland: Atmospheric rivers may become less frequent due to cooler surface air temperatures and reduced moisture.
• Antarctica: Atmospheric rivers account for 40 to 80% of summer meltwater in West Antarctic ice shelves, accelerating global sea level rise.
• Southern Hemisphere: Increased moisture is projected for southern Asia, the east coast of South America, and western Europe.

Mechanisms of Collapse

The AMOC relies on "deep water formation," where cold, salty water in the North Atlantic becomes dense enough to sink to the ocean floor. However, anthropogenic warming is disrupting this process. Rising air temperatures in the Arctic mean surface water cools more slowly, and melting ice caps dilute salt concentrations. This makes the water less dense, preventing it from sinking and creating a feedback loop that slows the entire system.

Research published in the Journal of Geophysical Research: Oceans suggests the timing of a collapse depends heavily on carbon emissions. In a scenario where emissions double between now and 2050, the AMOC could reach a tipping point as early as 2055. Under a "middle of the road" scenario, where global warming is kept to 4.8 degrees Fahrenheit above preindustrial levels, the collapse could begin in 2063. Professor Sybren Drijfhout of the University of Southampton estimates the overall chance of a collapse this century is about 50-50.

Socioeconomic and Environmental Risks

A full collapse would result in drastic changes. In Europe, the redistribution of heat could plunge northwestern regions into extreme cold, with some studies suggesting extremes of -20°C in London and -48°C in Oslo. Agricultural losses in Europe could reach about 30%, and tropical rain belts could shift southward, threatening food security for millions in West Africa and South Asia.

The American coast also faces significant risks. Sea levels along the US northeast coast are already rising faster than the global average, and a collapse could add another 50-100cm to those levels. Additionally, a 2025 study found that the current's recent weak phase has already contributed to up to 50% of flooding events along the US northeast coast since 2005.

Detection and Prevention

To better prepare, oceanographer René van Westen and colleagues developed an early warning signal based on salinity transport at the southern boundary of the Atlantic Ocean. According to the researchers, once a specific salinity threshold is reached, a tipping point is likely to follow within one to four decades.

Despite the gravity of the projections, some scientists emphasize that the outcome is not yet inevitable. A weakening of only around 20% was projected in the most optimistic scenario involving aggressive emissions reductions. Van Westen notes that a collapse could possibly be prevented if the world reaches net-zero carbon emissions around 2050.

Current efforts to separate human-caused decline from natural variability are ongoing. Scientists state they will need until at least 2033 to possess enough measurements to confidently distinguish the two.