Tropospheric ozone is a reactive gas that doesn’t come from direct emissions, but forms when nitrogen oxides react with volatile organic compounds, like methane, in sunlight. These chemicals mainly come from transportation, industry, livestock, and energy production. Ozone levels vary based on these pollutants and environmental factors, such as temperature and sunlight.

Unlike stratospheric ozone, which protects us from harmful UV rays, tropospheric ozone is a toxic pollutant that poses a threat to all living organisms, including plants, animals, and humans. In addition to its toxic effects, tropospheric ozone also contributes to climate change as a potent greenhouse gas.

Because ozone stays in the lower atmosphere between 6 and 27 days, it is considered a short-lived climate pollutant, or super pollutant. Reducing tropospheric ozone has an immediate positive impact on climate, bringing benefits mostly over the same regions that take actions to reduce its concentrations.

Levels of tropospheric ozone have risen significantly since the 20th century, with a climate impact similar to methane. Present decarbonization pathways alone are insufficient to mitigate the impact of ozone on climate, health and the environment. It is estimated that those pathways will result in single digit changes in ozone levels by 2045.

Tropospheric ozone (which includes ground-level ozone) also poses serious health risks, particularly for children, the elderly, and outdoor workers. Exposure can cause respiratory issues, reduce lung function, and exacerbate chronic conditions like asthma. It’s linked to nearly half a million premature deaths globally each year.

Lastly, tropospheric ozone has significant impacts on food security and biodiversity. Globally, it can reduce the yield of sensitive staple crops, such as wheat and soybeans, by up to 26%. Additionally, it contributes to a reduction of up to 11% in carbon capture by forests, exacerbating food insecurity and accelerating biodiversity loss. These effects threaten ecosystems and agricultural productivity.

Therefore, tropospheric ozone represents a gap in global climate strategy and an opportunity to prevent climate change, improve human health, and protect our ecosystem.