Ozone gas is significantly impeding the growth of tropical forests, resulting in an estimated 290 million tonnes of carbon going uncaptured annually, according to recent research.
Despite successfully protecting the ozone layer in the stratosphere against harmful ultraviolet radiation, ground-level ozone, a byproduct of human activities and sunlight, hampers plants’ capacity to absorb carbon dioxide and poses substantial risks to human health.
A new study by a team of researchers at the University of Exeter reveals a concerning finding – ground-level ozone is responsible for reducing the annual growth of tropical forests by an average of 5.1%.
Notably, the impact is even more pronounced in certain regions, with Asia’s tropical forests experiencing a notable 10.9% loss in new growth.
Tropical forests play a crucial role as “carbon sinks,” where they capture and store carbon dioxide that would otherwise remain in the atmosphere, helping to combat global warming.
“Tropical forests play a crucial role in mopping up our carbon dioxide emissions,” said co-lead author Dr Alexander Cheesman of James Cook University and the University of Exeter. “Our study shows that air pollution can jeopardize this critical ecosystem service.
“We estimate that ozone has prevented the capture of 290 million tonnes of carbon per year since 2000. The resulting cumulative loss equates to a 17% reduction in carbon removal by tropical forests so far this century.”
The researchers conducted experiments to assess the ozone vulnerability of diverse tropical tree species and subsequently integrated the findings into a comprehensive computer model of global vegetation.
The rise in “precursor” molecules, like nitrogen oxides, due to urbanization, industrialization, fossil fuel combustion, and fires has contributed to the formation of ozone.
“Ozone concentrations across the tropics are projected to rise further due to increased precursor emissions and altered atmospheric chemistry in a warming world,” said co-lead author Dr Flossie Brown, a recent graduate of the University of Exeter.
“We found that areas of current and future forest restoration – areas critical for the mitigation of climate change – are disproportionately affected by this elevated ozone.
“It is clear that air quality will continue to play an important but often overlooked part in the way forests absorb and store carbon.”
Professor Stephen Sitch, from the University of Exeter, added: “Embracing a future with greater environmental protection would lead to reduced ground-level ozone, thus improved air quality and the additional benefit of enhanced carbon uptake in tropical forests.”
Journal reference:
- Alexander W. Cheesman, Flossie Brown, Paulo Artaxo, Mst Nahid Farha, Gerd A. Folberth, Felicity J. Hayes, Viola H. A. Heinrich, Timothy C. Hill, Lina M. Mercado, Rebecca J. Oliver, Michael O’ Sullivan, Johan Uddling, Lucas A. Cernusak & Stephen Sitch. Reduced productivity and carbon drawdown of tropical forests from ground-level ozone exposure. Nature Geoscience, 2024; DOI: 10.1038/s41561-024-01530-1