Second-hand smoke is already one of the world’s largest preventable environmental health risks. But its significance is changing as climate change creates a more complicated air-pollution landscape.
A new global assessment estimates that 2.71 billion people were exposed to second-hand smoke in 2023, including 767 million children under 15. Exposure was associated with an estimated 1.66 million deaths and 44.8 million years of healthy life lost. The figures cover 204 countries and territories.
The immediate cause is tobacco smoke, not climate change. But the two crises increasingly intersect through a common pathway: the quality of the air people breathe.
That connection deserves much greater attention.
Second-hand smoke remains a massive global problem
The encouraging news is that the proportion of the world’s population exposed to second-hand smoke has fallen substantially. According to the latest assessment, exposure declined from 43.6% in 1990 to 33.9% in 2023.
Yet the absolute number of exposed people increased because global population growth has offset much of the progress.
That distinction is crucial.
A lower percentage does not necessarily mean fewer people are at risk. In 2023, hundreds of millions of children were still breathing tobacco smoke despite never choosing to smoke themselves.
Children are particularly vulnerable because their lungs and immune systems are still developing.
The climate connection is not as simple as saying climate change causes passive smoking
There is an important distinction between direct causation and overlapping environmental risks.
Climate change does not cause people to smoke, and it is not responsible for the toxic chemicals produced by cigarettes. The evidence instead points toward a broader environmental-health problem in which multiple sources of pollution can affect the same people.
Tobacco smoke can pollute indoor environments. Meanwhile, climate change is increasing the frequency or intensity of some extreme heat events and contributing to conditions that worsen wildfire risk in many regions.
That means people can increasingly face several air-quality threats at once.
The World Meteorological Organization has warned that climate-driven heatwaves and wildfires are undermining progress on air quality, with wildfire smoke and ground-level ozone becoming increasingly important pollution threats.
Children are caught between two environmental crises
The number of children exposed to second-hand smoke is particularly alarming when viewed alongside the growing climate risks facing younger generations.
UNICEF’s 2026 climate assessment says more than one billion children are exposed to at least three overlapping climate hazards. Children are also physically more vulnerable to environmental stresses because their bodies are still developing.
This creates a worrying convergence.
A child may live in a household where someone smokes, attend school in an area affected by urban pollution and then experience periods of extreme heat or wildfire smoke.
These exposures have different causes, but the health consequences can overlap—particularly for respiratory systems.
This is why environmental policy increasingly needs to look beyond individual pollutants and consider the total pollution burden experienced by vulnerable populations.
Climate change is making the air-pollution problem more complicated
For decades, many governments focused heavily on reducing pollution from vehicles, factories and power generation.
Those efforts remain essential.
But climate change is creating additional challenges. Hotter conditions can increase the formation of ground-level ozone, while hotter and drier conditions can contribute to dangerous wildfire conditions in vulnerable regions.
Wildfire smoke contains fine particulate matter and other pollutants that can penetrate deep into the respiratory system. The WMO says increasing wildfire smoke and heat-related ozone pollution are threatening recent improvements in air quality.
This means that even if governments successfully reduce some conventional sources of pollution, climate-related pollution can undermine those gains.
Tobacco control and climate policy should no longer operate in isolation
The second-hand smoke findings also expose a larger policy problem.
Health authorities often treat tobacco control, air pollution and climate policy as separate issues. But from the perspective of an ordinary family, they are not separate.
People breathe the same air.
A smoke-free home protects children from tobacco toxins. Cleaner transportation reduces urban pollution. Stronger climate policy can reduce the long-term risks associated with fossil-fuel emissions and climate-driven pollution. Better wildfire preparedness can reduce exposure during smoke events.
These policies can reinforce one another.
The latest second-hand smoke assessment says only about one-third of the world’s population was covered by comprehensive smoke-free legislation in 2024. Although coverage has expanded dramatically since 2007, major gaps remain.
The most dangerous mistake would be to treat indoor and outdoor air separately
Air pollution does not respect the boundaries between a house, street, school or workplace.
Second-hand tobacco smoke is often treated as a private household issue. Climate pollution is usually discussed as an outdoor environmental problem.
That separation can obscure the real exposure experienced by millions of people.
A child exposed to tobacco smoke indoors does not become protected simply because outdoor air is cleaner. Likewise, reducing household smoking does not eliminate exposure to wildfire smoke or ozone during extreme weather.
The solution therefore requires a broader concept of air-health protection.
Europe shows both progress and unfinished work
Europe has made considerable progress in reducing exposure to tobacco smoke.
The latest global analysis found particularly significant reductions in some European countries. Denmark and Norway recorded reductions in exposure of approximately 48.8% and 44.3%, respectively, since 1990. However, exposure in Central and Eastern Europe and Central Asia remained above the global average.
At the same time, Europe is experiencing increasingly visible climate-related air-quality pressures.
The summer of 2026 has brought severe wildfires across parts of southern Europe, while heat extremes and low river levels have highlighted the wider consequences of a warming climate.
The lesson is straightforward: progress against one pollution source does not mean the air-quality crisis has been solved.
The hidden danger is cumulative exposure
Perhaps the most important lesson from these developments is that public-health policy should increasingly focus on cumulative exposure.
A person does not breathe cigarette smoke in one category, wildfire smoke in another and ozone in a third. The lungs receive all of them.
Research published in Nature Human Behaviour this year also reinforces the scale of the health concerns associated with second-hand smoke. An umbrella review of 111 systematic reviews involving approximately 253 million participants found evidence linking exposure with several serious health outcomes, including lung cancer and cardiovascular disease.
This strengthens the case for treating second-hand smoke as an environmental health issue rather than simply a lifestyle issue.
What governments should do next
The policy response should be broader than simply telling smokers to quit.
Governments can strengthen smoke-free laws, increase tobacco taxation, restrict tobacco marketing, expand cessation services and protect children from household exposure.
At the same time, climate adaptation policies should include clean-air shelters, wildfire smoke warnings, better air-quality monitoring and protection for schools and hospitals during extreme pollution events.
UNICEF is similarly calling for climate adaptation measures that protect children and strengthen health, education, water and social-service systems against climate-related shocks.
The common objective is simple: reduce the amount of harmful pollution that reaches people’s lungs.
Clean air is becoming a climate issue
The second-hand smoke crisis should not be presented as evidence that climate change causes passive smoking. That would go beyond the scientific evidence.
The stronger argument is different.
Climate change and tobacco smoke are two distinct threats that increasingly converge through air quality and human vulnerability.
One is largely driven by tobacco consumption and exposure. The other is driven by greenhouse-gas emissions and a changing climate system. But both can increase environmental health risks, particularly for children and other vulnerable populations.
The 2.7 billion people exposed to second-hand smoke are therefore part of a much larger global warning.
The future of public health will not depend only on controlling individual pollutants. It will depend on whether governments can create environments where people—especially children—are protected from multiple, overlapping sources of harmful air.
Clean air is not merely a tobacco-control objective or a climate objective. It is becoming a fundamental public-health priority.
