New Delhi: Whatever the world spends to cut greenhouse gas emissions will be far outweighed by what it saves in health expenses because of a decline in disease and premature deaths from air pollution, scientists have said.

Their study shows that India and China will make the biggest health gains. It indicates that the number of premature deaths from air pollution in India between 2020 and 2050 could fall from an estimated 41 million to 22 million or even 19 million depending on how the world cuts its emissions.

Led by researchers in Spain, the study says the world will make health gains even if countries merely meet their current pledges - called nationally determined commitments (NDCs) - made under the 2015 Paris climate agreement.

The gains will be higher if countries act to prevent the global average temperature from rising beyond 1.5°C or even 2°C, says the study, published on Friday in The Lancet Planetary Health. The current pledges are not enough to meet a 2°C target.

According to the study, the cost of efforts aimed at achieving a 2°C target range from $22 trillion to $41 trillion, or 0.5 to 1 per cent of the global gross domestic product. But the health savings from reduced air pollution will be 1.6 to 2.5 times the mitigation costs, it adds.

"China and India, being the most populated and with the largest populations exposed to air pollution, will have higher positive impacts (health gains)," Jon Sampedro, a research scholar at the Basque Centre for Climate Change in Spain and a co-author of the study, told The Telegraph.

The health gains made by India and China will far outweigh their costs of climate-change mitigation efforts. But for the European Union and the US, their health savings alone would not offset their costs.

Anil Markandya, a professor at the Basque Centre who led the study, said that while earlier studies too had estimated the health gains from reduced air pollution, this was the first to calculate the benefit-cost ratios under different scenarios of emission reductions.

"We hope that the large health benefits we have estimated for different scenarios and countries might help policy-makers move towards adopting more ambitious climate policies and measures to reduce air pollution," Markandya said in a statement.

The new study "makes visible the very large, previously hidden health and economic benefits of climate mitigation and shows the benefits are greater than the costs of climate change prevention", said Philip Landrigan, an epidemiologist at the Icahn School of Medicine in Mount Sinai, US.