Australia's tropical rainforests are contributing more carbon to the atmosphere than they are extracting, a new study suggested - the first such response globally to climate change.
Researchers from Australia, Scotland and France analysed 49 years of data from 20 sites in the eastern state of Queensland encompassing some 11,000 trees.
The scientists found that increased extremes of high temperature and drought have led to more trees dying. From around the turn of the millennium, these trees' woody biomass - trunks, branches and leaves - has become a net source of carbon to the atmosphere rather than a sink.
"Tropical forests are among the most carbon-rich ecosystems on the planet. We rely on them more than most people realise," lead author Hannah Carle said in a Thursday release.
"Forests help to curb the worst effects of climate change by absorbing some of the carbon dioxide released from burning fossil fuels, but our work shows this is under threat."
Carle said that climate change is largely responsible for driving the increased tree mortality behind the release of higher levels of carbon.
"Regrettably, the associated increase in carbon losses to the atmosphere has not been offset by increased tree growth," the researcher said, adding that this could be a sign that "current models may overestimate the capacity of tropical forests to help offset fossil fuel emissions."
Co-author David Bauman said the team's finding "stresses the urgency to take action to reduce emissions, to allow these irreplaceable forests to continue to play their role slowing down global warming."
