Scaling up six climate and health interventions could prevent 1.56 million deaths and 16.67 billion tonnes of greenhouse gas emissions annually, according to WHO.
The measures could generate $3.92 trillion in annual economic welfare benefits and $5.44 trillion in fiscal benefits.
Five interventions with measurable costs could deliver an estimated $24 in benefits for every $1 invested.
Heat-health warning systems offer the highest return on investment, generating an estimated $835 in benefits for every $1 spent.
More efficient fossil fuel pricing, including removing inefficient subsidies, could deliver the largest overall economic gains, with substantial benefits for low- and middle-income countries.
Scaling up six climate and health interventions worldwide could prevent an estimated 1.56 million deaths annually, reduce greenhouse gas emissions and generate trillions of dollars in economic benefits, according to a new World Health Organization (WHO) report.
The report, Global benefits and costs of prioritized actions on climate change and health, estimated that implementing the measures globally could prevent 16.67 billion tonnes of carbon dioxide equivalent emissions each year.
It also projected annual economic welfare benefits of about $3.92 trillion and fiscal benefits of $5.44 trillion, largely driven by policies to price fossil fuels more efficiently.
The analysis examined six interventions: heat-health warning systems, climate-resilient drinking water, basic sanitation, hand hygiene, cleaner household energy and fiscal policies to improve fossil fuel pricing.
Together, these measures could deliver three benefits: improved public health, lower emissions and stronger economies.
"The climate crisis is a health crisis, but much of the harm it causes can be prevented with tools we already have," said WHO Director-General Tedros Adhanom Ghebreyesus.
He said scaling up proven interventions could save lives, particularly in countries facing the greatest health risks, and urged governments to place health at the centre of climate negotiations.
The WHO assessed the health, environmental and economic benefits of all six interventions. For five, it was also able to calculate implementation costs and returns on investment.
These five measures could generate approximately $24 in benefits for every $1 invested, with estimates ranging from $8 to $36 under different scenarios.
Heat-health warning systems offered the highest benefit-cost ratio, generating an estimated $835 in benefits for every $1 invested. Depending on the assumptions used, returns ranged from $364 to $1,272.
The report found that low- and middle-income countries could see particularly large benefits, potentially helping reduce health and economic inequalities.
Fiscal policies to price fossil fuels more efficiently, including removing inefficient subsidies, were projected to generate the largest overall economic benefits.
The WHO estimated annual economic welfare benefits of $3.04 trillion from these policies alone, with projections ranging from $691 billion to $5.34 trillion across different scenarios.
They could also generate fiscal benefits of approximately $5.44 trillion annually, although estimates varied depending on the assumptions used.
Unlike heat-health warning systems, fossil fuel pricing was not included in the calculation of the overall benefit-cost ratio because comparable implementation cost estimates were unavailable.
The report called on governments to prioritise and finance climate-health interventions, integrate health considerations into climate policies and strengthen resilience to climate-related risks.
It argued that existing measures could simultaneously reduce preventable deaths, cut greenhouse gas emissions and improve economic well-being, particularly in countries most vulnerable to climate change.