SYDNEY — Australia's tropical rainforests have become the first in the world to release more carbon than they absorb, in a trend linked to climate change, a study has found.

Rainforests are usually regarded as so-called "carbon sinks" as they absorb more emissions than they emit with new trees offsetting the carbon released by dead ones.

But a study looking at data from Queensland forests found that extreme temperatures have caused more tree deaths than growths.

The lead author of the study, which was published in science journal Nature, said the findings have significant implications for global emissions reduction targets which are partly based on how ecosystems — such as rainforests — can absorb carbon.

"Current models may overestimate the capacity of tropical forests to help offset fossil fuel emissions," said Dr Hannah Carle of the Western Sydney University.

With fewer new trees, the report found that the trunks and branches of dead trees — known as woody biomass — became carbon emitters, rather than carbon absorbers, about 25 years ago.

"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," said Dr Carle.

Dr Carle added that said an increase in trees dying in recent decades was due to climate change such as more extreme temperatures, atmospheric dryness and drought.

Based on 49 years of data from 20 forests in Queensland, the report also found a rise in the number of cyclones and the severity of them was killing more trees and making it harder for new ones to grow.

"We have in this study evidence that Australia's moist tropical forests are the first of their kind globally to to exhibit this [woody biomass] change," Dr Carle said.

"And that's really significant. It could be a sort of canary in the coal mine."

Senior author Patrick Meir also described the results as "very concerning", telling news agency AFP that it was "likely that all tropical forests [would] respond fairly similarly" — but added that more data and research would be needed to make a fair assessment.

Australia, one of the world's biggest polluters per capita, recently announced its new carbon reduction targets, pledging to cut emissions by at least 62% compared to 2005 levels over the next decade.

The country continues to face global criticism for its continued reliance on fossil fuels, with the government allowing one of the country's largest gas projects -Woodside's North West Shelf — to keep operating for another 40 years.

Last month, a new report into the impact of climate change found Australia had already reached warming of above 1.5C and that no community would be immune from "cascading, compounding and concurrent" climate risks. — BBC