Since approximately 2010, the rate of global warming has demonstrably intensified, precipitating a succession of historically warm years. The underlying causes for this phenomenon remain an area of considerable scientific inquiry and represent one of the most significant unresolved questions in contemporary climate science.
Our recent investigation elucidates that a primary contributor to this accelerated warming trend is the reduction in atmospheric pollution, particularly observed in China and other East Asian regions.
While the curtailment of sulfur emissions from international maritime activities has been previously identified in scholarly works as a potential factor, this regulatory shift only commenced in 2020. Consequently, its impact is deemed insufficient to fully account for the magnitude of this recent escalation.
Researchers at NASA have posited that alterations in cloud dynamics might play a role, potentially through diminished cloud cover over tropical regions or the North Pacific Ocean.
However, a factor that has not been extensively quantified is the profound impact of the substantial endeavors undertaken by East Asian nations, most notably China, to mitigate air pollution and enhance public health through the implementation of stringent air quality regulations.
Since around 2013, there has been a remarkable 75 percent decrease in sulfur dioxide emissions across East Asia. This pollution reduction effort accelerated precisely during the period when global warming began to intensify.
Our research specifically investigates the correlation between improvements in East Asian air quality and global temperature trends, building upon the foundational work of eight international climate modeling consortia.
We have ascertained that atmospheric pollutants may have effectively obscured the full extent of global warming. The ongoing improvement in air quality, conversely, is now likely exposing more of the human-induced warming driven by greenhouse gases.
In addition to being responsible for millions of premature fatalities, atmospheric pollution acts to shield the Earth’s surface from solar radiation, thereby inducing a cooling effect. The sheer volume of air pollution over recent decades has exerted a cooling influence, potentially suppressing human-induced warming by as much as 0.5°C over the past century.
As air pollution is progressively cleaned up – a vital undertaking for public health – this artificial solar screen is systematically dismantled. Given that greenhouse gas emissions have continued to rise, the consequence is an accelerated warming of the Earth’s surface.
Simulating the Impact of Pollution Reduction
Our research team employed 160 distinct computer simulations derived from eight global climate models. This comprehensive approach facilitated a more precise quantification of the effects that atmospheric pollution in East Asia has on global temperature and precipitation patterns.
We simulated a scenario of pollution reduction mirroring the actual reductions observed globally since 2010. Our findings indicated an additional global warming effect of approximately 0.07°C.
Although this figure is relatively modest when contrasted with the total global warming of roughly 1.3°C since 1850, it is nonetheless substantial enough to account for the recent acceleration in global warming, particularly when natural climate variability, such as the El Niño phenomenon impacting global weather patterns, is statistically removed.
Based on long-term trends, an expected warming of approximately 0.23°C since 2010 would have been anticipated.
However, the measured warming has been around 0.33°C. This discrepancy of an additional 0.1°C can largely be attributed to the air pollution cleanup in East Asia, along with other contributing factors such as modifications in shipping emissions and the recent amplified increase in atmospheric methane concentrations.
Air pollution induces a cooling effect by reflecting solar radiation or by altering cloud properties to enhance their reflectivity. The reduction in air pollution across East Asia influences global temperatures by diminishing the localized shading effect of pollutants over the region itself.
Furthermore, it leads to a reduction in transboundary pollution transported across the North Pacific, consequently lessening the amount of sunlight reflected by clouds in the eastern Pacific region.
The spatial distribution of these simulated climatic changes across the North Pacific aligns closely with observations derived from satellite data. Our modeling results and actual temperature records also reveal comparatively pronounced warming over the North Pacific, situated downwind from East Asia.
The primary driver of global warming remains greenhouse gas emissions, and the remediation of air pollution was both a necessary and long-overdue environmental action. This cleanup did not instigate the additional warming; rather, it removed a prior artificial cooling influence that had temporarily shielded us from some of the more severe consequences of climate change.
Global warming is projected to persist for many decades. Indeed, our historical and future greenhouse gas emissions will continue to exert an influence on the climate for centuries to come. However, atmospheric pollutants are typically short-lived in the atmosphere. Therefore, the recent acceleration in global warming stemming from this particular unmasking of its full effects may prove to be transient.
Laura Wilcox, Professor, National Centre for Atmospheric Science, University of Reading and Bjørn H. Samset, Senior Researcher in Climate and Atmospheric Sciences, Center for International Climate and Environment Research – Oslo
