Pacific heat waves linked to lower factory emissions from China

Reductions in aerosol emissions from Chinese factories may be partly responsible for recent heat waves in the Pacific Ocean, a new study has found.

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

Over the past decade, the North Pacific has experienced several such heat waves – known as “warm blob” events – leading to fish die-offs, toxic algae blooms and missing whales.

Such heat waves are generally attributed to global warming, although it is not known exactly why this 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 heat waves appeared to follow successful efforts by the Chinese government to reduce aerosol emissions from their country’s factories.

Why would reducing pollution warm the planet?

Aerosols are small particles commonly emitted when burning coal and oil. They can act as mirrors that float in the air and reflect the sun’s heat back into space.

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

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

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

Why might it be related to China?

Using computer models, the researchers found that heat waves in the Pacific Ocean appeared to coincide with efforts by the Chinese government to reduce pollution.

Starting around 2010, factories and power plants in China began to dramatically reduce emissions of aerosols such as sulfate, resulting in much cleaner air.

The researchers began collecting data and then entered it into twelve different computer climate models.

They conducted them under two conditions: one where emissions from East Asia remained as they had been for the past few decades, and one where they fell as they actually were.

They found that the models without drops did not produce much change elsewhere, while the models with aerosol drops showed heat waves in the northeastern parts of the Pacific Ocean.

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

That in turn intensified the low-pressure systems in the mid-Pacific Ocean, causing the Aleutian Low to expand and move south, weakening the westerly winds that typically cool the sea surface.

The result was warmer conditions.

The research could provide a warning for efforts at “solar geoengineering”: plans to purposefully reflect heat back into space using aerosols.

Such approaches – including the idea of ​​spraying aerosols into the air from a fleet of aircraft – have been discussed by academic institutions around the world.

Maria Rugenstein, a Colorado State University graduate, told Science.org that the research shows that the climate can respond quickly, and with unexpected consequences. She said: “I would consider this a cautionary tale.”