A weakening Atlantic Ocean current could dramatically reshape storm patterns across the Northern Hemisphere, bringing heavier, more damaging storms to California while leaving Greenland with less snowfall. That is the conclusion of new research from the University of California, Riverside, published in the journal Nature Communications.
The Atlantic Meridional Overturning Circulation, known as AMOC, functions like a massive conveyor belt for the planet's oceans. It carries warm tropical water northward toward Europe, then cools, sinks, and flows south along the ocean floor. Scientists have already observed it slowing, but the downstream effects on storm systems far from the Atlantic have been less clear.
As Science Daily reported, doctoral student Mohima Mimi led the research and found that the ripple effects of a weakening AMOC extend well beyond Europe.
"It is well known that the AMOC is a big player in the world's climate system, and that it is slowing down. What we didn't know is exactly how the AMOC might impact atmospheric moisture and storms outside the Atlantic region," Mimi said.
The study found that a weaker AMOC would alter ocean temperatures in ways that change how much moisture the atmosphere can hold. It would also strengthen high-altitude winds that guide storms across the Northern Hemisphere. Those winds would push more moisture toward the West Coast of North America, amplifying atmospheric rivers.
Atmospheric rivers are long, narrow corridors of water vapor that carry moisture from tropical regions toward higher latitudes. For California, they already supply a large share of the state's annual water. They also cause flooding.
"In California, atmospheric rivers are a double-edged sword," Mimi said. "They supply much of the state's water supply, but as they become stronger, they're likely to also bring widespread destruction."
The modeling projects these changes under a high greenhouse gas emissions scenario in which AMOC continues weakening throughout the century. Under that scenario, more atmospheric rivers would also develop along the eastern coast of South America and around Antarctica.
The effects on Greenland would move in the opposite direction. Fewer storms would reach the island, leading to reduced snowfall and slower ice accumulation. That outcome carries its own consequences, since Greenland's ice sheet is a major factor in global sea level.
The researchers noted that flood risks in California could rise, putting pressure on infrastructure and water management systems already strained by the state's cycles of drought and deluge.
Mimi said the study fills a gap in climate science by connecting Atlantic circulation changes to Pacific weather in concrete terms. The work suggests that decisions about emissions reductions carry consequences not just for the Atlantic region, but for storm behavior thousands of miles away.
