Rainfall in Asia decides harvests, fills rivers, and supports billions of people. The monsoon is not just weather; it is crucial for survival.

Scientists once thought the main monsoon drivers were located close by in the Himalayas and the Tibetan Plateau. That picture is now incomplete. New research shows that distant North America also fuels Asia’s summer rains.

The finding changes how we see global weather. It shows that climate is not local, no matter how it feels. A hot summer in one part of the world can help shape storms and rainfall across an ocean.

Testing continents for monsoon

Researchers from the University of Bristol and the Chinese Academy of Sciences used powerful climate models to test how continents matter. They first created a “water world” without land. Then they added continents step by step.

Most additions made only small changes. Africa pushed more rain into the Indian Ocean. Australia had little effect. Antarctica barely registered.

But when North America entered the picture, rainfall in Asia jumped. In some areas, the boost reached nearly a quarter more rain than before.

Heat as a monsoon driver

Why would North America matter so much? Land heats faster than oceans. In summer, North America turns into a giant heat source.

That heating lowers pressure and strengthens the high-pressure system over the North Pacific. Winds push harder toward Asia, pulling ocean moisture westward. The result is stronger monsoon rains.

This matches the Rodwell-Hoskins theory: heat in one region creates waves that ripple through the atmosphere. Those waves can strengthen or weaken storms far away. In this case, North America’s summer heat pushes more water into Asia’s skies.

Tibet and beyond

The Tibetan Plateau remains the heavyweight in this story. Its height and heat lift huge columns of air, feeding the monsoon. But the new study shows Tibet is not alone.

North America produces about half as much effect on East Asia’s rainfall as Tibet. And in India, the distant continent sometimes has more influence than the Tibetan Plateau.

“In the past few decades, when people talk about what factors would drive such a strong monsoon in Asia, they always looked at the Eurasian and African continents, especially the Himalaya and Tibetan region,” said study lead author Linlin Chen from the University of Bristol.

“These are indeed large influences. But we know Earth climate is closely connected, and now we have more evidence to show precisely how.”

North America and monsoon strength

The researchers also tested whether the ocean played a role. They fixed sea surface temperatures in the models and looked again. The rainfall increase faded.

Next, the team isolated the role of land. The effect came roaring back. The land itself, not the surrounding water, drives the teleconnection.

This is significant because people change land faster than seas. Farming, urban growth, and deforestation in North America could all shape monsoon strength thousands of kilometers away. The connection is real, and it carries human fingerprints.

Geological history backs up the finding. Around 100 million years ago, parts of North America lay under a shallow seaway. Asia’s monsoon was weaker then.

When the land rose back, heating returned and rainfall grew stronger. The story of continents moving and reshaping climate is written deep in Earth’s past. The same forces still operate today, though now amplified by human activity.

Earth’s deeply connected systems

“This study reveals how deeply connected the Earth’s climate systems are: local changes can trigger global effects. Everyone is responsible for both the local and global climate changes,” said study co-author Paul Valdes.

That responsibility is clear. The Asian monsoon feeds over a billion people. It also brings deadly floods when it swings too far.

Knowing that summers in North America can tip the balance means climate policy cannot stay regional. What happens in one place spreads everywhere.

Future risks for monsoon season

The study also shows why models must include both oceans and atmosphere together. Past work sometimes used only atmospheric models, missing crucial feedbacks.

By using fully coupled models, the team uncovered important connections that had remained hidden.

As the planet warms and land use changes, the ties between continents will grow tighter. North America’s heat will not stay at home. It will ride the winds and help decide whether Asia sees bounty or disaster in the rains.

The study is published in the journal Science Advances.

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