Nearly 99% of people worldwide are exposed to harmful air pollution, the UN says.
Pollution contributes to nine million deaths annually, mostly in low- and middle-income nations.
Climate change is intensifying wildfires, waste emissions and the formation of dangerous particles.
Cities such as Delhi, Tehran and Lagos continue to record high PM2.5 levels despite global declines.
UNEP warns climate, pollution and biodiversity crises are now costing trillions of dollars each year.
Air pollution and climate change are reinforcing one another in a “vicious cycle” with devastating consequences for human health and ecosystems, a United Nations report has found, with nine million deaths each year linked to pollution-related diseases.
Climate change is worsening the effects of air pollution and waste generation, accelerating biodiversity loss, land degradation and desertification, found the Global Environment Outlook-7 (GEO-7), published on December 9, 2025 by the UN Environment Programme (UNEP).
The report warned that 99 per cent of the world’s population is exposed to some form of air pollution and more than 90 per cent of the nine million deaths occur in low- and middle-income countries.
The report says the combined pressures of warming temperatures, rising greenhouse gases, waste mismanagement and deteriorating air quality are driving “substantial adverse health effects and related economic losses” across the globe.
“Environmental pollution is the world’s largest risk factor for disease and premature death, with nine million human deaths annually attributable to some form of pollution. More than 90 per cent of pollution-related deaths occur in low and middle-income countries,” the paper said.
Air pollution now affects nearly the entire global population through exposure to trace gases, plastic particles, particulate matter, heavy metals and greenhouse gases (GHG), the report noted.
Atmospheric concentrations of long-lived GHGs such as carbon dioxide and nitrous oxide, and short-lived ones like methane (CH4), ozone, and some hydrofluorocarbons are impacting the Earth’s radiative balance. Polluting particles are either emitted directly from combustion, industry, transport, fires, road and soil dust, or formed secondarily from gaseous precursors such as sulphur dioxide (SO2), nitrogen oxides, ammonia and non-methane volatile organic compounds.
While sulphur dioxide and nitrogen dioxide levels fell in Western Europe and North America between 2000 and 2019, concentrations have risen across parts of Asia, the report said. “From satellite measurements, global SO2 emissions trends over 2005-2021 are negative. By contrast, CH4 emissions from human activities increased by around 20 per cent from 2000-2020,” the report said.
Landfills and waste management facilities remain among the top three global sources of methane, with emissions often two to three times higher than reported because of unmonitored leaks and legacy dumps, the paper added.
The report finds that fine particulate matter (PM2.5) concentrations fell across 13,160 cities in North and Central America, Europe, sub-Saharan Africa and Southeast Asia between 2000 and 2019. Cities such as London and Beijing have recorded improvements, but high pollution levels persist in megacities such as Delhi, Tehran and Lagos.
Firework displays during traditional or religious festivals led to sharp spikes in particulate matter concentrations in countries such as Mexico and India, the report identified. Open burning of waste in landfills and informal sites continues to be a major uncontrolled source of pollution.
Nanoparticles from fossil fuels, transport and industry, which are rarely monitored in air quality networks, pose an emerging urban health risk, the report pointed out. Growing evidence also suggested microplastics are affecting regional and transboundary air quality, with potential impacts on human health.
Air pollution’s links to respiratory and cardiovascular disease are well established, but the report also highlights associations with cognitive decline, type-2 diabetes and dementia, including in children.
UNEP cautioned that wildfires and climate change are locked in a self-reinforcing cycle impacting human health, ecosystems and agriculture. “Climate change directly affects the frequency and magnitude of extreme weather, including high temperatures and prolonged droughts, that are conducive to the outbreak and spread of wildfires in many regions,” it said.
Human-induced climate change has increased the global temperature trend to 0.26°C per decade between 2014 and 2023. The World Meteorological Organization confirmed that global average temperature in 2024 reached 1.55°C above pre-industrial levels.
Rising temperatures affect tropospheric ozone and secondary aerosol formation, as many atmospheric chemical reactions are temperature-dependent. These interactions contribute to a continued positive Earth energy imbalance, further intensifying the climate crisis.
Climate change is making wildfires more intense and longer-lasting too. Their number has increased worldwide over the decades and continues to rise, thanks in part to changes in land use.
These fires, in turn, drive up greenhouse gas emissions, destroy forests, raise PM2.5 levels and deepen climate impacts. Wildfire activity is projected to increase significantly without stronger international action, with the probability of global wildfire occurrence rising from 1.31 today to 1.57 by 2100.
Groups most at risk from wildfire smoke include people with existing respiratory, cardiovascular or neurological illnesses, older people, outdoor workers, pregnant women, infants and primary caregivers, UNEP pointed out.
The report also cites the war between Russia and Ukraine as an example of how conflict can severely undermine air quality. Cities in the conflict zone saw average PM2.5 concentrations rise by about 9.8 per cent, nitrogen dioxide by 10.1 per cent, and a 7.9 per cent fall in tropospheric ozone levels.
UNEP also warned that climate change, biodiversity loss, land degradation and pollution are already costing the world trillions of dollars annually, with impacts expected to escalate sharply under current development pathways.