Cleaner Air Is Contributing to Global Warming — Study

Last Updated on: 27th July 2025, 03:04 pm

The law of unintended consequences is cruel. When the things we do with the best of intentions give us results that confound our expectations, it leads to cognitive dissonance and an urge to understand why our expectations were not met. We all want cleaner air — for ourselves, for our children, for our planet.

In 2020, the International Maritime Organization mandated low-sulfur fuels for ships that follow its rules (many do not). As a result, global sulfur dioxide emissions fell by about 10 percent. That’s good. So why did average global temperatures increase? Because it turns out that sulfur dioxide in the atmosphere tends to mask the warming effect of carbon dioxide.

“Sulfur particles contained in ships’ exhaust fumes have been counteracting some of the warming coming from greenhouse gases. But lowering the sulfur content of marine fuel has weakened the masking effect, effectively giving a boost to warming,” Carbon Brief reported a year ago.

Sulfur & Carbon Emissions

Last week, University of California–Riverside announced a new study published in Communications Earth & Environment that claims cleaner air in East Asia, particularly China, may be partially responsible for a spike in average global temperatures in recent years. “Cleaner air,” in this instance, means lower sulfur dioxide levels — exactly what happened with ship emissions.

The study found that East Asia’s aerosol reductions contributed about 0.05 degrees Celsius per decade to global temperatures since 2010, which accounts for most of the acceleration in warming observed during this period. The trend persists even after accounting for natural fluctuation events like El Niño.

“When something like the anomalous, record breaking warmth of 2023 and 2024 happens, climate scientists start to wonder if there’s a factor we’re missing,” said Robert Allen, climatology professor at the University of California, Riverside. “This study was our effort to figure out what that might be.”

Lead author Bjørn Samset, a senior researcher at the Center for International Climate and Environmental Research in Norway, said the answer became increasingly clear through multiple model simulations. “The spike in warming aligns with a dramatic drop in aerosol pollution from China’s skies.”

The findings are based on simulations from eight major climate models. Data came from the Regional Aerosol Model Intercomparison Project, or RAMIP, which includes contributions from modeling centers in the United States, Europe, and Asia.

Since 2010, China has implemented aggressive air quality policies, slashing sulfur dioxide emissions by roughly 75 percent. Before these policies were enacted, pollution was a leading cause of premature death in China. But fewer cooling aerosols in the atmosphere also mean intensified warming, especially over East Asia. The region is expected to face more extreme heat, shifting monsoon patterns, and possible disruptions to agriculture.

Allen quite correctly calls the cleanup a double-edged sword. “Reducing air pollution has clear health benefits, but without also cutting CO₂, you’re removing a layer of protection against climate change. It highlights the need for parallel efforts to improve air quality and reduce greenhouse gas emissions.”

Aerosols like sulfur dioxide do not remain in the atmosphere for a significant amount of time. “Sulfur dioxide and sulfate aerosols have lifetimes of about a week. Once they’re removed, we’ll eventually settle back into a warming rate that’s more consistent with the long term trend,” Allen added.

Cleaner Air, Hotter Planet

The study reinforces that carbon dioxide and methane remain the dominant drivers of long term climate change, UC Riverside says. “Our study focused on the recent, dramatic speedup in global warming, which is very concerning but still small compared to the overall, long-term amount of warming from increased CO2 and methane,” Samset said. Other regions, including South Asia, Africa, and North America, are also beginning to phase out aerosol emissions. RAMIP researchers plan to analyze how these shifts could shape climate trends in the years ahead. Samset and his co-authors wrote in the abstract to their study:

“Global surface warming has accelerated since around 2010, relative to the preceding half century. This has coincided with East Asian efforts to reduce air pollution through restricted atmospheric aerosol and precursor emissions. A direct link between the two has, however, not yet been established.

“Here we show, using a large set of simulations from eight Earth System Models, how a time-evolving 75% reduction in East Asian sulfate emissions partially unmasks greenhouse gas driven warming and influences the spatial pattern of surface temperature change.

“We find a rapidly evolving global, annual mean warming of 0.07 ± 0.05 °C, sufficient to be a main driver of the uptick in global warming rate since 2010. We also find North Pacific warming and a top-of-atmosphere radiative imbalance that are qualitatively consistent with recent observations. East Asian aerosol cleanup is thus likely a key contributor to recent global warming acceleration and to Pacific warming trends.”

Geoengineering Rears Its Ugly Head

All this chatter about sulfur dioxide is making people start talking about … geoengineering. Why? Because putting sulfur dioxide back into the atmosphere could potentially cool our fragile planet, which is beginning to overheat dangerously. Remember that law of unintended consequences? That is what scares the bejeezus out of those who have not drunk deeply of the geoengineering Kool-Aid.

“It’s a card we might have to play if we’re pushed into a corner,” Robert Allen said. “But it comes with a host of risks, including disrupted rainfall patterns, food insecurity, and political tensions. Air quality improvements are a no-brainer for public health, but if we want to prevent the worst impacts of climate change, we have to cut CO₂ and methane too. The two must go hand in hand.” [Emphasis added]

The problem is, for many people, geoengineering is just a convenient excuse for continuing to burn fossil fuels. Rather than address the existential threat they represent, those advocates — who are raking piles of profits — are saying, “Don’t worry about carbon dioxide. Just keep pumping into the atmosphere. Some technology will come along to offset the damage we are doing — carbon capture, geoengineering, unicorn farts — so just keep doing what you are doing and don’t worry.”

Michael Barnard wrote a few months ago about one startup peddling dreams of rainbows made from pixie dust and how misguided such ventures can be. And what happens when some lunatic finds himself in a position of power and decides to end geoengineering attempts because he finds them to be part of a green new scam or the product of “wokeness?” What then?

Once geoengineering starts, it can’t be stopped without huge risk of an increase in global temperatures as a result. It’s not like turning your back on pledges made in Paris in 2015. It’s a genuine, gold plated threat to the future of humanity. Why take that risk when the path forward is so clear — a full fledged embrace of renewable energy and a circular economy? Politics is an open invitation to experience the law of unintended consequences first hand — to the detriment of every living thing on Earth. Surely humans are too smart to take that risk … aren’t they?