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 generally considered “carbon sinks” because they absorb more emissions than they emit, with new trees offsetting the carbon released by dead trees.
But a study looking at data from Queensland forests found extreme temperatures caused more tree deaths than growth.
The lead author of the study, published in the scientific journal Nature, said the findings have significant implications for global emissions reduction targets, which rely in part on how ecosystems – such as rainforests – can absorb carbon.
“Current models may overestimate the ability of rainforests to help offset fossil fuel emissions,” said Dr Hannah Carle of 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 curb the worst effects of climate change by absorbing some of the carbon dioxide released by burning fossil fuels, but our work shows this is under threat,” Dr Carle said.
Dr Carle added that the increase in dead trees in recent decades was due to climate change, including more extreme temperatures, atmospheric dryness and drought.
Based on 49 years of data from 20 Queensland forests, the report also found an increase in the number of cyclones and their severity was killing more trees and making it harder for new ones to grow.
“We have evidence in this study that Australia’s tropical rainforests are the first of their kind in the world to exhibit this phenomenon. [woody biomass] change,” said Dr. Carle.
“And that’s really significant. This could be sort of a canary in the coal mine.”
Lead author Patrick Meir also called the results “very worrying”, telling the AFP news agency that it was “likely that all tropical forests [would] react quite similarly” – but added that more data and research would be needed to make a fair assessment.
Australia, one of the world’s largest per capita polluters, recently announced its new carbon emissions reduction targets, pledging to reduce its emissions by at least 62% from 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 – the northwest Woodside Shelf – to continue operating for another 40 years.
Last month, a new report on the impact of climate change found Australia had already reached warming above 1.5°C and no community would be safe from “cascading, cumulative and concurrent” climate risks.
