The Hidden Role of Sulphur Pollution in Accelerating Global Warming
Cleaner air may be revealing the true pace of climate change.
1The Debate Over Clean Air and Climate
During Britain's record-breaking summer of 2023, a debate erupted on social media about the causes of heatwaves. Richard Tice, deputy leader of Reform UK, claimed that cleaner air, not carbon dioxide, was driving higher temperatures. While his assertion about CO2 was incorrect, it highlighted a lesser-known aspect of climate science: the role of sulphur pollution in cooling the Earth.
2Two Types of Pollution
Fossil fuels emit both carbon dioxide and sulphur pollution. CO2 is well-known for its warming effect, but sulphur pollution forms tiny particles that reflect sunlight back into space, partially offsetting global warming. Clean-air policies, like the US Acid Rain Program in the 1990s, have drastically reduced sulphur emissions, removing this cooling effect.
3The Accelerating Pace of Warming
The past three years have been the warmest on record, and 2027 is predicted to surpass 2024 as the hottest year ever. Scientists believe the reduction in sulphur aerosols is slightly speeding up global warming. This raises concerns that the planet may be more sensitive to greenhouse gases than previously thought.
4Natural Climate Fluctuations
Global temperatures naturally fluctuate due to phenomena like El Niño, which temporarily raises temperatures. However, researchers like Reto Knutti at ETH Zurich have stripped out these natural variations to reveal an underlying acceleration in the rate of global warming.
5The Role of Aerosols
Sulphur dioxide from burning coal and oil forms sulphate aerosols, which reflect sunlight and cool the planet. These aerosols also influence cloud formation, making clouds brighter and longer-lived. Ship pollution, for example, creates visible trails in marine clouds, enhancing their reflective properties.
6The Greenhouse Analogy
Sulphur pollution acts like dust on greenhouse windows, reducing the amount of sunlight that enters. As clean-air policies reduce sulphur emissions, it’s as if we’re wiping dust off the windows, allowing more sunlight in and accelerating warming.
7Health and Environmental Costs
While sulphur pollution cools the planet, it also harms human health and causes acid rain, which damages forests and aquatic life. Countries have spent decades cutting sulphur emissions, leading to significant reductions in Europe, North America, and China.
8Short-Lived Cooling Effect
Unlike CO2, which remains in the atmosphere for centuries, sulphate aerosols last only days or weeks. When sulphur emissions fall, their cooling effect disappears almost immediately. This has contributed to an estimated half-degree increase in summer warming in western-central Europe since 1980.
9Quantifying the Impact
Climate scientist Piers Forster estimates that declining aerosol pollution adds 0.05C to 0.1C of warming per decade. While significant, this is overshadowed by the 0.2C per decade warming caused by greenhouse gases. Aerosols have masked some of the earlier warming caused by greenhouse gases.
10The Bigger Picture
Cleaner air is not causing global warming but is revealing its true pace by removing the cooling effect of sulphur aerosols. This underscores the urgent need to address greenhouse gas emissions, which remain the primary driver of climate change.
Original article: BBC News — The Hidden Role of Sulphur Pollution in Accelerating Global Warming