Just weeks before the 2008 Beijing Olympics, Chinese authorities restricted half of all private cars from the city’s roads, alternating daily bans for number plates ending in even and odd numbers.

The radical move was just one of a suite of measures aiming to curb the city’s choking smog, alongside factory closures and halts on construction.

Over decades of intensive development, residents had become accustomed to smog that not only caused untold respiratory and health problems but was also threatening to derail the Games.

Even after the haze cleared, complaints by athletes and visiting media clouded the Games’ legacy, spurring a renewed campaign of pollution reduction in China.

As China’s economy kept growing after 2008, its emissions of aerosols — small particles in the air, distinct from greenhouse gases — peaked and then dropped rapidly.

Aerosols can include particles emitted by burning fossil fuels, others by volcanic eruptions or bushfires — even airborne sea salt is considered an aerosol.

When enough of them are concentrated in one place, haze can become visible, and weather conditions, including temperature and rainfall, may be impacted.

Likewise, when emissions are reduced, that can cause a significant change, too.

Such has been the success of China’s air-cleaning effort since the 2010s that researchers have now linked it to changes in weather far beyond its borders, including in Australia.

Researchers have also tied it to global temperature rises as the aerosols’ masking effect on global warming is diminished.

Reflecting heat, changing rain

Unlike greenhouse gases, which trap heat in the atmosphere, most aerosols reflect sunlight away from Earth and produce a cooling effect.

CSIRO scientist Melita Keywood likened their effect to the colour of a roof over a home.

“In some countries where it’s cold, you might want to have a black roof, but in Australia you probably want to have a white roof.”

Many aerosols also interact with water vapour in the air, affecting clouds and rainfall both positively and negatively.

Late in 2025, a team of Chinese researchers published a paper linking Australia’s hot and dry weather in the 2010s to China’s aerosol reductions.

They found weather systems were impacted thousands of kilometres across the Pacific, reducing moisture across large parts of Australia and significantly raising the risk of bushfires in all states and territories.

Despite Australia’s relatively high rainfall since 2020, Nanjing University of Information Science and Technology professor Yang Yang, who was among the study’s authors, said changes in China had continued to impact Australian weather.

“The marked increase in Australian rainfall after 2020 does not invalidate conclusions about the influence of Chinese aerosols on Australia’s climate,” he said.

“Rather, it indicates that during this later period, large-scale climate variability exerted a stronger influence.”

Multiple climate scientists said more work was needed to properly understand the effect of China’s emissions reduction on Australian weather.

Nonetheless, some researchers have argued the effect of China’s clean-up has been felt even further afield.

From China across the globe

Last year, a team of mostly European climate scientists labelled East Asian aerosol reductions as the biggest reason for the acceleration of global warming since 2010.

One of them, Finnish Meteorological Institute researcher Joonas Merikanto, said China’s changes had disrupted continental weather patterns, spreading the impact.

“It affects the local circulation patterns over the Pacific and, for example, influences the monsoon precipitation over the Asian region,” he said.

Scientists frequently liken the impact of removing pollution to “unmasking” or “revealing” warming that had already been caused by greenhouse gas emissions.

Decades before China’s emissions peaked, Europe’s effort to cut pollution demonstrated this effect.

“[Europe] was heavily polluted in the 80s,” Leipzig University professor of theoretical meteorology Johannes Quaas said.

Climate scientist Karsten Haustein estimated that most central European countries had experienced almost 3 degrees Celsius of warming since pre-industrial times, exacerbated when the cooling effect of that pollution was removed.

“Probably a bit more than a degree of extra warming was essentially just hidden by the aerosols,” he said.

Hazy understanding

In 2024, Tim Cowan was among a group of researchers who found Asian aerosol emissions had increased Australia’s monsoon rainfall in the decades before China’s historic clean-up.

“Observations show a significant increase in Australian summer monsoon rainfall since the mid-twentieth century,” the researchers wrote in a paper published in The Journal of Climate.

This aligns with Professor Yang’s assertion that China’s reduction of its aerosol emissions had the opposite effect on Australian rainfall from 2013.

However, there are relatively few papers besides these to compare the results with.

Dr Cowan said Australia was probably not pulling its weight in aerosol research.

Dr Keywood agreed Australia had not placed as much research attention on aerosols as other countries and said they would become more important as the climate warms.

“It’s something that’s kind of always been in the hard basket because it’s quite [computationally] intensive,” she said.

This is particularly true when studying rainfall, one of the most closely watched weather statistics in Australia.

Knowing how Australian rain might be affected by Chinese aerosols is made harder by the different effects of the particles and complex weather systems transporting them across the Pacific.

“One of the key things you need to produce rain is a cloud condensation nuclei particle, and it turns out that the things that are really good at that are like sulphate,” Ms Keywood said.

“But [other aerosols] like black carbon don’t like water.”

More changes coming

While scientists unpack the consequences of China’s dramatic smog reversal, more of Australia’s Asian neighbours are seeking to emulate its success.

In India and Bangladesh, air pollution is a persistent and deadly problem linked to millions of excess deaths each year and, increasingly, acidic rainfall.

Climate experts agree it is imperative to reduce the pollution, but acknowledge it will likely increase heating and extreme weather in the South Asian region.

“From the temperature point of view, there will definitely be a local increase,” Dr Haustein said.

However, when asked how this might affect the Pacific and Australia, Dr Haustein was hesitant to make such clear predictions.

“Disentangling the remote effects [of aerosols], not only the regional effects … it’s crazy difficult,” he said.

Only 2,000km from Australia, Indonesia’s capital Jakarta, now recognised by the UN as the world’s largest city, also ranks among the most polluted metro areas.

“I think the issue now for Australia is we feel like we’re fairly far removed from the problem [of aerosol pollution],” Dr Cowan said.

“I think our understanding of the role aerosols play in driving our climate … it’s fairly rudimentary.”