Pacific heatwaves linked to lower factory emissions from China

Reductions in emissions of aerosols from Chinese factories may be partly to blame for recent heatwaves in the Pacific, a new study has said.

The study, published in the Proceedings of the National Academy of Sciences, suggests that repeated marine heatwaves over the past decade could be linked to reduction in pollution from factories in China.

Over the past decade, the north Pacific has experienced multiple such heatwaves – also known as "warm blob” events – leading to fish die-offs, toxic algae blooms and missing whales.

Such heatwaves have been generally attributed to global warming though it is unknown exactly why it could cause such sudden and variable increases in a specific part of the planet.

The research team of oceanographers and scientists from China, the US and Germany noted that the onset of the heatwaves appeared to follow successful efforts by the Chinese government to reduce aerosol emissions from their country's factories.

Why would a reduction in pollution warm the planet?

Aerosols are small particles that are commonly emitted from burning coal and oil – they can act like mirrors floating in the air, reflecting heat from the sun back into space.

Efforts to curb pollution can sometimes have a paradoxical effect of warming up areas nearby, due to the fact that tiny aerosol particles in the air can ‘reflect’ the sun’s heat back into space.

In the oceans, for example, efforts to curb pollution from ships have been linked to a warming effect due to lower aerosol emissions from shipping.

Earlier research efforts have suggested that massive reductions of aerosols in one place could lead to warming in other places.

Why could it be linked to China?

Using computer modelling, the researchers found that heatwaves in the Pacific seemed to coincide with efforts by the Chinese government to reduce pollution.

Beginning around 2010, factories and power generating plants in China began dramatically reducing emissions of aerosols such as sulphate, resulting in much cleaner air.

The researchers began collecting data and then input it into 12 different computer climate models.

They ran them under two conditions – one where emissions from East Asia remained as they were over the past several decades and one where they dropped in the way they actually had.

They found that the models with no declines did not cause much change elsewhere, whereas those with aerosol drops showed heatwaves occurring in the northeast parts of the Pacific Ocean.

As less heat was reflected back into space over China, warming of coastal regions in Asia began, resulting in the development of high-pressure systems.

That, in turn, made low-pressure systems in the middle Pacific more intense, resulting in the Aleutian Low growing bigger and moving south which weakened the westerly winds that typically cool the sea surface.

The result was hotter conditions.

The research could offer a warning about efforts in ‘solar geoengineering’ - plans to deliberately reflect heat back into space using aerosols.

Such approaches - including the idea of spraying aerosols into the air from a fleet of planes - have been debated by academic institutions around the world.

Speaking to Science.org, Maria Rugenstein, a Colorado State University said that the research shows the climate can respond rapidly, and with unexpected repercussions. She said: “I would take this as a cautionary tale.”