Ambitious climate action to improve global air quality could save up to more than 1 million lives per year by 2040.

However, the research, led by Cardiff University, found developing countries will rely heavily on international cooperation to see these benefits, because much of their pollution originates outside their borders.

The first-of-its-kind study analysed these cross-border pollution “exchanges” for nearly every country – 168 in total.

The study revealed how a fragmented world, with little collaborative climate mitigation policymaking, would lead to greater health inequality for poorer nations who have less control over their own air quality.

The team focused on the impact of fine particulate matter (PM_2.5), exposure to which is the leading environmental risk factor for premature deaths globally.

Lead author Dr Omar Nawaz from Cardiff University’s School of Earth and Environmental Sciences, said: “While we know climate action can benefit public health, most research has ignored how this affects the air pollution that travels across international borders and creates inequalities between countries.

“Our analysis shows how climate mitigation decisions made in wealthy nations directly affect the health of people in the Global South, particularly in Africa and Asia.”

The team, which included researchers at the University of Colorado Boulder, used advanced atmospheric modelling and NASA satellite data to simulate different future emissions scenarios for the year 2040.

Together with a health burden estimation, these data enabled the researchers to understand who benefits – and assess different levels of dependency – when countries implement climate mitigation policies.

“We wanted to see how the health benefits of action on climate change could differ when there is greater or weaker global cooperation,” explained Nawaz.  “We were surprised to find that although Asia sees the most total benefits from climate action to its large share of the population, African countries are often the most reliant on external action, with the amount of health benefits they get from climate mitigation abroad increasing in fragmented future scenarios.”

The team’s projections also show the balance of pollution flowing across borders may shift, even when total global air pollution declines.

“This is vital information for policymakers and global aid organisations as they seek to address climate change challenges amidst domestic and international priorities,” the study added.

Co-author professor Daven Henze of the Department of Mechanical Engineering at the University of Colorado Boulder added: “Some climate policies could inadvertently make air pollution inequalities worse, specifically for developing nations that might rely heavily on their neighbours for clean air. It’s thus not sufficient to focus only on domestic co-benefits. More inclusive climate strategies entail explicitly accounting for evolving transboundary inequalities.

“Holistic climate policy should therefore evaluate how dependent a nation is on others’ emissions reductions, how mitigation scenarios reshape air-pollution flows across borders, and whether global efforts are helping or harming equity.”