More than 8 million people died in 2018 as a result of air pollution from fossil fuels, according to researchers at the University of Harvard. Previous estimates have put the total number of global deaths at 4.2 million, however, this study has highlighted that the death toll is much greater than previously suggested.

In 2018, more than 8.7 million people around the globe died from fossil fuel pollution, the report estimates. That’s twice as many as the 4.2 million people suggested by the previous research – the Global Burden of Disease. This means that air pollution from burning fossil fuels such as coal and diesel was responsible for about one in five deaths worldwide, as per the report.

Previous research relied on satellite and surface observations to estimate the average global annual concentrations of airborne particulate matter, known as PM2.5. The problem is, satellite and surface observations can’t tell the difference between particles from fossil fuel emissions and those from dust, wildfire smoke or other sources. “With satellite data, you’re seeing only pieces of the puzzle,” said Loretta J. Mickley, Senior Research Fellow in Chemistry-Climate Interactions at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and co-author of the study. “It is challenging for satellites to distinguish between types of particles, and there can be gaps in the data.”

To overcome this, the Harvard researchers used GEOS-Chem, a global 3D model of atmospheric chemistry to estimate the emissions from multiple sectors, including power, industry, shipping, aircraft and ground transportation and then they simulated detailed oxidant-aerosol chemistry. They found that the regions with the highest concentrations of fossil fuel-related air pollution were in Eastern North America, Europe and South-East Asia.