Smog in Beijing. Efforts in reducing aerosol emissions in China have been successful, but they could ... [+]
Over the course of the past decade, China’s clean air policies have produced substantial results in reducing the emissions of pollutants and alleviating the production of harmful aerosols. However, a new research paper suggests China’s success in improving air quality could actually make climate change mitigation efforts more difficult by unmasking the global warming which aerosols previously “hid.”
The study, which involves researchers across institutions including the Carnegie Institution for Science and the Chinese Academy of Environmental Planning, used climate models to analyze the results of China’s emission reduction efforts. Their simulations showed the decrease in atmospheric aerosols could end up leading to a more than 0.1 degree Celsius increase in global temperatures over the northern hemisphere.
Aerosols are the tiny liquid and solid particles which are suspended in the air as the result of either natural or human activity. Anthropogenic aerosols, such as those created by the burning of fossil fuels, hang lower in the atmosphere. There, the particle matter can be breathed lungs, where it burrows, causing health problems. But beyond being a serious issue of public health, aerosols also are known to have a role in the fluctuation of Earth’s temperature due to their ability to both absorb and reflect incoming solar radiation.
Aerosols and Radiative Forcing
The researchers used simulations to model the effects of clean air policies enacted in China between the years of 2006 to 2017.
They found the emission changes affected radiative forcing, which denotes the difference between sunlight absorbed by the Earth and the energy radiated back. This disparity in absorption and radiation causes global temperature fluctuations. If more energy is being absorbed than is being reflected, temperatures will rise and if more energy is reflected than absorbed, temperatures will cool.
Over the course of the years the researchers analyzed, sulphur dioxide levels in China were reduced by an incredible 70 percent. Sulfate aerosols, a by-product of sulphur dioxide emissions, are also naturally expelled during volcanic eruptions. The eruption of Mount Pinatubo in the Philippines in 1991 was a major factor in leading climatologists to confirm the resulting sulfate aerosols have a cooling effect on Earth’s temperatures because they reflect back such a large portion of incoming radiation.
Sulfate aerosols from volcanic eruptions have such a cooling effect that some scientists have considered mimicking the natural process by dispersing them in the atmosphere via plane as a climate change mitigation strategy. However, while this would lead to the intended drop of temperature, models have shown this approach also would have some potentially disastrous consequences, such as reduced global rainfall.
The substantial reduction in sulphur dioxide emissions lessens this cooling effect, which effectively reveals the global warming it previously masked.
Over the same time period in which sulphur dioxide emissions were reduced, carbon dioxide emissions in China grew by more than 50 percent. With less sulfate aerosols to reflect radiation, the increase in greenhouse gases has further amplified carbon dioxide’s global warming effect.
Still, the researchers of the study view the reduction in aerosols as a “win” for climate causes, despite warming effects. While China’s air pollution reduction efforts may unmask global warming, good air quality is still crucial to public health.
On the other end of radiative forcing, China also reduced black carbon emissions which absorb incoming sunlight. Knowing how changes in these different aerosol concentrations affect global temperatures will be critical in crafting climate change mitigation strategies. The researchers suggest policies which simultaneously target both aerosol emissions and greenhouse gases will be the most successful in addressing global warming.
