Australian rainforests ‘no longer a carbon sink’

SYDNEY

Australia's tropical rainforests are among the first in the world to start leaking more carbon dioxide than they absorb, scientists said on Thursday as they linked the worrying trend to climate change.

The world's rainforests are typically thought of as crucial "carbon sinks," sucking huge quantities of planet-heating emissions from the atmosphere.

But new research has found rainforests in Australia's northern tropics have become net carbon emitters, "the first globally to show this response to climate change."

"Forests help to curb the worst effects of climate change by absorbing some of the carbon dioxide released by burning fossil fuels," said lead author Hannah Carle, from Western Sydney University.

"But our work shows this is under threat."

The researchers pored through records charting the growth of Queensland's rainforests over almost 50 years.

Extreme temperatures and severe droughts linked to climate change were making it harder for trees to grow, they found.

Trees store carbon dioxide in their trunks and branches as they grow but release the gas into the atmosphere when they die.

"Tropical rainforests are among the most carbon-rich ecosystems on the planet," said Carle.

"The change our study describes is largely due to increased tree mortality driven by climate change, including increasingly extreme temperatures, atmospheric dryness and drought. Regrettably, the associated increase in carbon losses to the atmosphere has not been offset by increased tree growth."

Co-author Adrienne Nicotra said it "remains to be seen whether Australian tropical forests are a harbinger for other tropical forests globally."