California is familiar with atmospheric rivers in the same way as those who live around the coast are familiar with hurricanes, based on what they leave behind and the names people give them. An estimated $30 billion in damage was inflicted by the storms that pounded the state during the winters of 2022 and 2023, flooding agriculture in the Central Valley, submerging mountain villages, and turning rivers brown. They were referred regarded as historic events by scientists. According to a recent study that was published in Nature Communications in May, the term “historic” may grow increasingly commonplace as the century goes on, and it has nothing to do with the Pacific.
The vast network of ocean currents known as the Atlantic Meridional Overturning Circulation, or AMOC, works essentially as a worldwide heat conveyor. From the tropics, warm, shallow water travels northward, releasing heat into the atmosphere over the North Atlantic before cooling, sinking, and cycling back south over the ocean floor.
As increasing water temperatures interfere with the density differences that propel this system, scientists have seen indications that it is slowing down. Researchers at UC Riverside have now modeled a particular downstream effect that was previously unidentified: a decreasing AMOC appears to intensify the atmospheric rivers that strike California’s coast throughout the winter through a series of atmospheric and oceanic reactions.
At first, the mechanism is not intuitive. California is thousands of kilometers away from the Atlantic. However, Mohima Sultana Mimi, a doctoral student and lead author of the study, explains that a slowing AMOC modifies ocean temperature patterns in ways that impact the amount of moisture the atmosphere can hold. Crucially, it seems to intensify the high-altitude westerly winds that drive Pacific storms eastward. More moisture is carried toward the coast by stronger winds. According to climate model simulations, by the end of the century, atmospheric rivers will reach California more frequently and with greater intensity.
It’s important to be clear about what this study claims and doesn’t. This modeling work is conducted under a high-emissions scenario, where greenhouse gas emissions stay high and the AMOC continues to decline throughout the course of the century. It is based on the results of a single study team rather than a firmly established scientific consensus, and it is not a definitive prediction of any particular storm season. According to a 2025 study published in Nature, under high forcing, AMOC deteriorated but did not completely collapse across 34 climate models, in part because Southern Ocean upwelling maintained some circulation. The UCR study’s California result doesn’t require a collapse; progressive weakening is sufficient. However, climate experts are still truly unsure about the extent of this weakening and how rapidly it occurs.
The mechanism that the results identify is what lends them credibility. Rearranging atmospheric circulation far enough downstream to boost Pacific winds due to cooling in the North Atlantic is a physically coherent pathway rather than a theoretical one. The modeling team deliberately isolated the impact of the AMOC from other warming-related changes using coupled climate simulations. Even in cases when there is still uncertainty regarding exact magnitudes, that level of methodological attention makes the finding more difficult to reject.
This narrative is challenging to distilll into a straightforward warning because the consequences cut both ways. Infrastructure that California has spent decades developing to handle water scarcity rather than abundance is threatened by stronger atmospheric rivers, which also raise the risk of flooding and overload drainage systems. When storms surpass design criteria, the infrastructure collapses swiftly, as seen by the 2023 flooding in Pajaro, where a levee breach drowned an agricultural hamlet for weeks.
However, more intense atmospheric rivers also bring potential, according to senior author Wei Liu, if communities make investments in additional reservoir capacity, better forecasting, and more intelligent water capture systems. Since its extreme wet-dry fluctuations in recent years revealed the vulnerability of treating water only as something to drain away, California has been investigating precisely those investments.
