A UNEP and Climate and Clean Air Coalition study says 25 measures across six sectors would return around $15 for every dollar spent. Each year of delay, it says, costs more than $1.5 trillion.
Governments have long booked climate policy as a cost. They have treated dirty air as the price of growth. A report published on 7 September by the UN Environment Programme and the Climate and Clean Air Coalition argues the opposite. Tackle both problems together, it finds, and every dollar spent returns around $15.
Its title is Hidden Assets. It is the first global economic study of joint action on climate and air quality. UNEP released it on the International Day of Clean Air for blue skies. Its central claim is that the joint return beats tackling either problem alone, because the same sources and policies drive both.
Inger Andersen, Executive Director of UNEP, said the findings overturn an old assumption. “For too long, we have treated climate action as a cost to be managed and air pollution as the unfortunate outcome of development,” she said. “This report shows the opposite: clean air is a key driver of development, health, food and energy security, and climate stability.”
What the 25 measures would return
The package covers six sectors: energy, industry, transport, farming and food, home cooking and heating, and waste. It mixes long-term decarbonisation with steps aimed at super pollutants such as methane, black carbon and HFCs. For instance, it includes renewable power, tighter vehicle standards, electric vehicles and an end to routine venting and flaring. It also covers manure and fertiliser management and a phase-down of HFCs.
The yearly benefits would equal 2.8 per cent of global GDP in 2035. By 2050 that rises to 4.5 per cent, and by 2100 to 11.4 per cent. For comparison, explicit fossil fuel subsidies took 2.18 per cent of global GDP in 2022. Even without the non-market welfare gains, the measures still return about $4 per dollar.
Delay is expensive. The report puts the cost of each lost year at more than $1.5 trillion, or 0.5 per cent of GDP. Weak enforcement and fragmented decision-making could push full delivery back by almost eight years. Removing those barriers could add up to $10 trillion in health benefits by 2040.
The health case
Air pollution is the second pillar of the argument. The report links outdoor pollution from PM2.5 and ozone to an estimated 6.4 million premature deaths in 2025. Household air pollution added a further 2 million, including around 300,000 children.
The study also counts the cost of illness, which earlier work left out. It ties 5.5 million new cases of childhood asthma and 2 million new cases of dementia to outdoor air pollution in 2025. Millions of heart attacks, strokes and cancers sit alongside them. Full delivery of the measures could therefore prevent 144 million premature deaths by 2050.
Climate gains and the finance gap
On the climate side, prompt action would halve global carbon dioxide emissions by 2050 and cut methane by 60 per cent. Black carbon, sulphur dioxide and nitrogen oxides would fall by around 70 per cent. As a result, the measures would avoid roughly 0.34C of warming by 2050 and 1.4C by 2100.
Elliott Harris, independent co-chair of the assessment, said the returns would draw capital in any other field. “A benefit-cost ratio of 15 to 1 would attract capital instantly in almost any other sector,” he said. “Finance ministries and investors who keep climate and air quality in separate budget lines are leaving trillions on the table.”
Simon Dietz co-chaired the assessment and is Professor of Environmental Policy at the London School of Economics. He said modelling the two problems together changed the answer. “When we modelled them together, the returns were larger than each could show alone, because the same sources, sectors and policies so often drive both,” he said.
The report calls for joint planning across climate, air quality, health and the economy. It also wants stronger enforcement and closer coordination of public and private finance. Many of the measures pay back within a single term of government, the authors add. That is a timescale ministers can act on.
