A decline in aerosol emissions from Chinese factories may be partly to blame for the recent heat wave in the Pacific Ocean, a new study says.
The study, published this week in the Proceedings of the National Academy of Sciences, suggests that repeated ocean heatwaves over the past decade may be linked to reduced pollution from Chinese factories.
Over the past decade, the North Pacific has experienced several such heatwaves (also known as “warm blobs”), causing fish die-offs, toxic algae blooms, and missing whales.
Although such heat waves are generally thought to be caused by global warming, it is unclear exactly what causes such sudden and variable increases in heat waves in certain regions of the planet.
A research team of oceanographers and scientists from China, the United States and Germany said the onset of the heat wave appears to be the result of successful efforts by the Chinese government to reduce aerosol emissions from its factories.
Why does reducing pollution make the earth warmer?
Aerosols are small particles commonly released from the combustion of coal or oil that act like mirrors suspended in the air, reflecting heat from the sun back into space.
Efforts to curb pollution can have the paradoxical effect of warming nearby regions, as small aerosol particles in the air can “reflect” the sun's heat back into space.
For example, in the ocean, efforts to reduce pollution from ships are associated with the warming effect of reducing aerosol emissions from ships.
Previous research efforts have suggested that large reductions in aerosols in one location can lead to warming elsewhere.
Why is it associated with China?
Using computer modeling, researchers found that the Pacific heatwave appears to coincide with efforts by the Chinese government to reduce pollution.
Starting around 2010, Chinese factories and power plants began significantly reducing emissions of aerosols such as sulfates, resulting in much cleaner air.
The researchers began collecting data and inputting it into 12 different computer climate models.
They performed the experiment under two conditions. One condition is that emissions from East Asia have remained the same for the past several decades, and the other condition is that actual emissions have decreased.
They found that models without the reduction did not cause significant changes in other regions, but models with aerosol droplets produced heat waves in the northeastern Pacific Ocean.
As less heat was reflected back into space over China, coastal regions of Asia began to warm, resulting in the development of an anticyclone.
As a result, the central Pacific low pressure system became more intense, which caused the Aleutian Low to grow larger and move south, weakening the westerly winds that normally cool the ocean surface.
The result was hotter conditions.
The study could raise a warning about efforts at “solar geoengineering,” which involves using aerosols to intentionally reflect heat back into space.
Such approaches, including the idea of spraying aerosols into the air from fleets of planes, have been discussed at academic institutions around the world.
Colorado State University's Maria Rugenstein told Science.org that the study shows that the climate can react quickly and have unexpected effects. “I want to take this as a warning,” she said.
