/cloudfront-us-east-2.images.arcpublishing.com/reuters/YCHI7RNDAJNMTJFB4U3OCDATPY.jpg)
Nov 2 (Reuters) – New findings suggest that air pollution, although a grave health hazard that causes millions of deaths annually, is actually shielding the Earth from the full impact of the sun. Paradoxically, eliminating air pollution would accelerate climate change. Scientists studying China’s successful 10-year “war on pollution” have reached this unsettling conclusion. China’s efforts to reduce pollution, particularly sulfur dioxide (SO2) emissions from coal plants, have resulted in a nearly 90% decrease in SO2 levels and the saving of countless lives, as confirmed by Chinese official data and health studies.
However, the removal of the toxic shield provided by air pollution, which scatters and reflects solar radiation, has led to a rise in China’s average temperatures of 0.7 degrees Celsius since 2014. This increase in temperature has caused more intense heatwaves, according to meteorological data and expert interviews conducted by Reuters.
This dilemma, referred to as a “Catch-22” by atmospheric chemist Patricia Quinn of the U.S. National Oceanic and Atmospheric Administration (NOAA), demonstrates the interconnectedness of cleaning up air pollution and the potential consequences of doing so on global warming. The phenomenon of removing air pollution, known as “unmasking,” may have had a more significant impact on temperatures in some Chinese cities than greenhouse gas emissions alone over the past decade, according to experts. They warn that other heavily polluted regions, such as India and the Middle East, would experience similar temperature increases if they follow China’s lead in reducing sulfur dioxide emissions and the resulting polluting aerosols.
The experts highlight the potential for efforts to improve air quality inadvertently driving the world towards catastrophic levels of warming and irreversible climate impacts. According to Paulo Artaxo, an environmental physicist and lead author of a chapter on short-lived climate pollutants in the most recent Intergovernmental Panel on Climate Change (IPCC) report, aerosols currently mask one-third of global warming. Hence, implementing technologies to reduce air pollution would significantly accelerate global warming in the short term.
The Chinese and Indian environment ministries have not yet responded to requests for comment on the effects of pollution unmasking. However, the IPCC’s 2021 report recognized the link between reducing sulfur dioxide pollution and warming, stating that, without the protective shield of SO2, global average temperatures would have already risen by 1.6 degrees Celsius above preindustrial levels, surpassing the goal of limiting warming to 1.5 degrees Celsius.
Reuters’ review of Chinese data provides the most comprehensive understanding to date of how pollution unmasking is manifesting in the real world. The data analysis includes previously unreported numbers on temperature changes and SO2 emissions over the past decade, corroborated by environmental scientists. The analysis involved interviews with a total of 12 scientists, including four who have contributed to or reviewed sections on air pollution in IPCC reports.
While climate experts do not suggest easing efforts to combat air pollution, which poses a clear and immediate danger and causes approximately 7 million premature deaths annually, they emphasize the need for more aggressive action to reduce emissions of greenhouse gases. One promising approach in the short term is to prioritize the reduction of methane emissions to offset the effects of pollution unmasking.
China’s President Xi Jinping pledged to combat pollution upon assuming power in 2012, following decades of coal-burning that had made China the world’s factory. In 2013, the government launched its version of the U.S. Clean Air Act in response to record smog in Beijing, ominously referred to as the “Airpocalypse.” This led to the closure of hundreds of inefficient factories, the implementation of stricter vehicle fuel standards, and the mandatory use of lower-sulfur coal in power plants and steel mills. Consequently, China’s SO2 emissions decreased from nearly 26 million metric tons in 2006 to 2.7 million metric tons by 2021, representing an 87% reduction.
The reduction in pollution coincided with a rise in temperatures. According to Reuters’ calculations based on yearly weather reports, China’s national average annual temperatures have increased by more than 0.7 degrees Celsius since 2014, reaching 10.34 degrees Celsius. Scientists differ in their estimates of how much of this temperature increase is attributed to pollution unmasking versus greenhouse gas emissions or natural climate variations.
Local temperature increases near pollution sources, such as heavy industrial regions, were immediately observed in China due to pollution unmasking. Climate scientist Yangyang Xu, who models the impact of aerosols on the climate at Texas A&M University, estimates that unmasking has caused temperatures to rise by almost 1 degree Celsius near the cities of Chongqing and Wuhan since the mid-2000s, when sulfur emissions peaked. On heatwave days, the unmasking effect becomes even more pronounced, with computer simulations suggesting that the rapid decline in SO2 in China could increase temperatures by as much as 2 degrees Celsius. Scientists warn that these temperature increases pose significant risks in a country like China, which already experiences dangerous heatwaves.
The effects of pollution unmasking are most acute in developing countries, as the United States and Europe have already taken significant steps to reduce pollution in previous decades. However, the impacts of pollution unmasking can also be felt in distant regions. A study published in 2021 suggests that the decrease in European aerosol emissions since the 1980s may have altered weather patterns in Northern China.
In India, sulfur pollution levels have actually increased in the past two decades, approximately doubling according to researchers from NOAA. In 2020, when pollution significantly decreased due to COVID-19 lockdowns, ground temperatures in India were the eighth warmest on record, 0.29 degrees Celsius above the 1981-2010 average. India aspires to achieve an air cleanup similar to China’s and introduced its National Clean Air Program in 2019 to reduce pollution in more than 100 cities by 40% by 2026. If India and other polluted regions in the Middle East follow China’s example and improve their air quality by transitioning to green energy sources, they too will experience the loss of the protective shield provided by sulfates.
As the consequences of pollution unmasking become more apparent, experts are exploring various methods to counteract the associated warming. One proposal involves deliberately injecting sulfur aerosols into the atmosphere as a form of “solar radiation management” to cool temperatures. However, many scientists are concerned about the potential unintended consequences of this approach. Another widely supported plan is to reduce methane emissions since methane’s effects on the atmosphere are short-lived. Cutting methane emissions would yield relatively quick results in mitigating global temperatures.
