During an unusually hot summer, a public debate emerged on social media regarding the causes of rising global temperatures, with one prominent figure incorrectly suggesting that reduced pollution rather than carbon dioxide was the primary driver of warming. However, the underlying scientific phenomenon is more nuanced and potentially significant than initially claimed.
Fossil fuel combustion produces two distinct types of pollution with opposing climate effects. While carbon dioxide traps heat in the atmosphere, sulphur pollution creates tiny particles that reflect sunlight back into space, providing a cooling influence. Decades of clean-air regulations in Europe, North America, and China—such as the US Acid Rain Program of the early 1990s and shipping industry rules—have sharply reduced sulphur emissions, though carbon dioxide levels remain near record highs. As sulphate aerosol concentrations decline, their temporary cooling effect diminishes almost immediately, whereas greenhouse gases persist in the atmosphere for centuries.
Research suggests that this loss of the aerosol cooling effect is accelerating global warming. One study estimates it has added approximately half a degree to summer warming in western-central Europe since 1980, while another indicates declining aerosol pollution may now contribute 0.05C to 0.1C of warming per decade. The three warmest years on record have occurred recently, and forecasts indicate 2027 is very likely to become the warmest year yet. Scientists have determined that some of this acceleration represents a removal of masking—the aerosols had previously hidden the full warming effect of greenhouse gases rather than causing new warming.
Despite the significance of the aerosol effect, greenhouse gas emissions remain the dominant driver of warming, currently adding approximately 0.2C per decade globally. This raises a broader question for climate scientists: whether the planet may be more sensitive to greenhouse gases than previously understood, potentially indicating faster climate change than anticipated. Energy balance analyses examining how much solar radiation Earth absorbs versus heat lost to space continue to inform these assessments.
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