Australia’s tropical rainforests have become the first in the world to release more carbon than they absorb, a study has found, in a trend linked to climate change.
Rainforests are often viewed as so-called “carbon sinks” because they absorb more emissions than they emit, with new trees offsetting the carbon emitted by dead trees.
But a study that looked at data from Queensland forests found that extreme temperatures caused more trees to die than to grow.
The lead author of the study, published in the scientific journal Nature, said the findings have important implications for global emissions reduction targets that depend in part on how ecosystems – such as rainforests – absorb carbon.
“Current models may overestimate the ability of tropical forests to help offset fossil fuel emissions,” said Dr. Hannah Karl from Western Sydney University.
With fewer new trees, the report found that dead tree trunks and branches – known as woody biomass – became carbon emitters, rather than carbon absorbers, about 25 years ago.
Dr Karl said: “Forests help limit the worst effects of climate change by absorbing some of the carbon dioxide released from burning fossil fuels, but our work shows that this is under threat.”
Dr Karl added that the increase in tree mortality in recent decades was due to climate change such as extreme temperatures, drying of the atmosphere and drought.
Based on 49 years of data from 20 forests in Queensland, the report also found a rise in the number and intensity of cyclones is killing more trees and making it difficult for new ones to grow.
“In this study we have evidence that Australia’s wet tropical forests are the first in the world to show this [woody biomass] “Change,” Dr. Karl said.
“And that’s really important. It could be kind of the canary in the coal mine.”
Senior author Patrick Meir also described the findings as “deeply worrying”, telling AFP that “it is likely that all tropical forests… [would] “It responds fairly similarly” — but she 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 over its continued reliance on fossil fuels, with the government allowing one of the country’s largest gas projects – North West Woodside – to continue operating for another 40 years.
Last month, a new report on the impact of climate change found that Australia had already reached temperatures of more than 1.5 degrees Celsius, and that no community would be immune to “cascading, multiplying and simultaneous” climate risks.