Ozone emissions reduce tropical forests' ability to store CO2, study says

Ozone emissions caused by human activity are reducing the productivity of tropical forests and their ability to store carbon, Australian-led research has found.

According to a new study, published by Australia's James Cook University (JCU) on Friday, elevated levels of ozone at ground level have significantly affected the ability of tropical forests to collect and store carbon dioxide (CO₂) from the atmosphere.

The researchers measured the ozone susceptibility of various tropical trees at a purpose-built experimental facility in the northeast Australian city of Cairns and then incorporated their findings into a global vegetation model.

"We found that current ozone caused by human activity resulted in a substantial decline in annual net primary productivity (NPP) – the net uptake of CO₂ from the atmosphere – across all tropical forests," Alexander Cheesman, lead author of the research from the Cairns-based JCU and the University of Exeter in the United Kingdom, said in a media release.

Between 2005 and 2014, the research said ozone produced by human activity reduced tropical forest NPP by an average of 5.1 percent.

"We calculate that this productivity decline has resulted in a cumulative loss in carbon drawdown to tropical forests, the removal of carbon from the atmosphere by this critical ecosystem, of about 17 percent in the 21st century," Cheesman said.

Ozone is a molecule made up of three oxygen atoms. It is one of several naturally occurring gases that make up the Earth's atmosphere and filter out damaging ultraviolet radiation from the sun.

However, ozone at ground level, caused by emissions of precursor chemicals from human activity, is damaging to human health and is the main component of smog.

The authors of Friday's study said ozone concentrations across the tropics are projected to rise further and that areas of current and future forest restoration are disproportionately affected by elevated ozone levels.