The North American continent plays a critical but overlooked role in strengthening the Asian summer monsoon, intensifying seasonal rainfall over India and East Asia by as much as 23 percent, according to a new study published in Science Advances.

Researchers from the University of Bristol and the Chinese Academy of Sciences found that North America acts as a powerful heating center in the Northern Hemisphere, triggering atmospheric teleconnections that funnel more moisture toward Asia.

The finding challenges long-standing assumptions that the Tibetan Plateau is the main driver of the monsoon system, which sustains more than a billion people across South and East Asia.

Lead author Linlin Chen, a climate scientist at the University of Bristol, said the results reveal a missing piece in monsoon science.

“Our study shows that North America’s landmass is not just a passive bystander but an active player in driving the strength of the Asian summer monsoon,” Chen said. “This influence is comparable to that of the Tibetan Plateau in some regions, especially when it comes to sustaining rainfall over India.”

Rainfall Gains Comparable to Tibet

Using a coupled atmosphere–ocean climate model, the team simulated the effects of adding or removing individual continents.

They discovered that the presence of North America increases East Asian summer monsoon rainfall by 1.28 millimeters per day or 32 percent and Indian summer monsoon rainfall by 0.63 mm per day or 14 percent, compared with scenarios without the continent.

Across the broader region, precipitation rose by nearly 2 mm per day, marking North America’s contribution as comparable to, and in some cases more critical than, Tibet’s influence.

The mechanism works through large-scale circulation shifts. Heating over North America strengthens the North Pacific subtropical high, drives poleward movement of the Hadley circulation, and intensifies low-level winds that transport moisture into Asia.

These teleconnections persist even when the Tibetan Plateau is factored in, suggesting that multiple remote landmasses jointly shape monsoon intensity.

“Tibet has always been considered the dominant factor, but our work shows that North America supplies about half the rainfall boost over East Asia and can actually offset Tibet’s weakening effect on the Indian monsoon,” Chen said.

Climate Change Implications

While Tibet boosts East Asian rainfall by 34 percent, it suppresses Indian monsoon precipitation by 41 percent in the model. North America, in contrast, increases Indian rainfall by 28 percent, partly offsetting Tibet’s weakening effect.

Chen said the findings highlight broader risks in a warming world. “What happens in North America — whether through land use change or climate-driven heat extremes — can ripple across the Pacific and affect rainfall for billions of people in Asia,” she said.

Although the simulations rely on simplified land-sea configurations, the authors argue that their results provide a conceptual baseline for understanding monsoon evolution through Earth’s history and its sensitivity to continental positions.

They caution, however, that more realistic models including detailed topography and vegetation are needed to confirm the robustness of the findings.

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