New research shows that air pollution from Europe more than a century ago may have reshaped weather patterns across Asia, intensifying the Asian summer monsoon and influencing rainfall for millions of people.

As industrialisation spread across Europe in the 20th century, emissions from this region rose. As well as greenhouse gases such as carbon dioxide and methane, increasing quantities of sulphate aerosol particles were being released from burning fossil fuels. Sulphate aerosols can artificially cool the Earth’s climate by reflecting sunlight before it can reach the ground, and by triggering the formation of clouds.

Scientists have used climate models and historic weather data to understand how European air pollution might have been a factor in how summer monsoons changed in Asia in the first half of the 20th century. South Asia saw increased rainfall, while parts of East Asia became drier.

The models accurately predicted how Asian summer monsoons changed as increased air pollution in Europe caused the continent to cool. This is an important step in validating the accuracy of these models, which scientists can now use to predict how the climate will react to current and future emissions.

Dr Ioana Colfescu, a research scientist at NCAS and the University of St Andrews, explains how the atmosphere of the past can give us vital clues to the atmosphere of the future.

“Using advanced climate model experiments, we found that increases in European sulphate aerosol emissions during the early 1900s cooled the continent’s surface enough to trigger a ripple effect in the atmosphere – one that reached all the way to South and East Asia,” explains Ioana.

She adds: “This sulphate-induced cooling set off a large‑scale wave pattern high in the atmosphere, altering winds and moisture transport. The computer model result was a wetter monsoon season in South Asia and a southward shift of monsoon rainfall in East Asia, which closely matches historical observations.”

The Asian summer monsoon provides water for more than 60% of the world’s population, so any shift in its intensity or location has consequences for agriculture, water security, and risks related to floods or droughts.

“With European sulphur emissions now declining, our modelling study suggests that monsoon responses may change direction again. This is an important insight for climate forecasting and resilience planning across Asia,” outlines Ioana.

The study highlights how human-driven pollution in one part of the world can affect climate and weather systems far beyond national borders, and why understanding past changes is crucial for predicting future monsoon behaviour as sulphur emissions continue to decline.