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Why air pollution is sometimes good news for the climate

In December talks in Paris involving more than 200 countries may result in a new agreement aimed at reducing carbon emissions. In the months leading up to the conference, The Economist will be publishing guest columns by experts on the economic issues involved. Here, Stefan Ambec of the Toulouse School of Economics and Jessica Coria of the University of Gothenburg argue that efforts to reduce greenhouse-gas emissions and efforts to reduce other pollutants are not always complementary.

BURNING fossil fuels for heating, generating electricity or for transport does not simply produce carbon-dioxide emissions, but also other greenhouse gases (GHG), such as particulate matter (PM), sulphur dioxide (SO2), nitrogen oxides (NOx) and volatile organic compounds (VOC). They are harmful to human health and damage the environment. Local air pollution is a big concern in many countries, and measures to reduce carbon-dioxide emissions have been implemented to combat this. China has recently issued a national five-year action plan to cut air pollution, by reducing the use of coal in generating electricity, and by encouraging investment in wind power and improved energy efficiency.

At first, this appears to be good news for the climate. The general public often thinks that measures to improve local-air quality will also cut carbon emissions. Yet this is not the full story. Policies to cut carbon emissions sometimes also cause a rise in the emissions of other greenhouse gases, such as SO2 and NOx, which contribute to climate change even more than carbon does. For instance, filtering SO2 emissions out by installing flue-gas desulphurisation devices on coal boilers uses energy, thereby creating more carbon emissions. Most notably, over the last decade fuel-tax policy in Europe has incentivised drivers to switch from petrol cars to diesel ones, cutting carbon-dioxide emissions but increasing ones from more NOx and PM.

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