The Forest That Exhales

October 28th, 2025
Dhruv Arun

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. Tropical forests usually act as “carbon sinks,” absorbing carbon dioxide from the atmosphere and storing it within their stems and branches. Now, a new study finds, one Australian rainforest is doing the opposite.

The research, published in Nature, analyzed data from around 11,000 trees in northeastern Australia tracked for nearly 50 years. Nearly half a century of data from tropical forests across Queensland revealed that this crucial carbon sink is now under threat. The study found that the forests have been emitting more carbon than they absorb for roughly 25 years.

Rainforests are typically able to offset emissions as new trees grow to replace dying ones. But extreme temperatures have caused more tree deaths than growth. Drier air, higher temperatures and drought are all contributing factors. From 1971 to 2000, tracked plants absorbed about 553 pounds of carbon per acre each year, but from 2010 to 2019, they emitted about 830 pounds per acre annually.

The change, which affects tree trunks and branches but not roots, marks the first time a tropical rainforest has shifted from a carbon sink to a carbon source. With fewer new trees, the trunks and branches of dead ones, known as woody biomass, became emitters rather than absorbers. Tree deaths resulting from cyclones have further reduced the rainforest’s capacity to store carbon. A rise in the number and severity of cyclones has killed more trees and made it harder for new ones to grow.

Lead author Dr. Hannah Carle of Western Sydney University said the phenomenon could reflect a declining ecosystem in Australian wet rainforests overall. She explained that Australia’s moist tropics “occupy a bit of a warmer, drier climate space than tropical forests on other continents,” making them a preview of what other rainforests may face. Dr. Carle said more frequent drought and atmospheric dryness driven by climate change are increasing tree mortality.

Senior author Patrick Meir described the results as “very concerning,” adding that it is likely all tropical forests will respond similarly. Professor Adrienne Nicotra from the Australian National University said it remained to be seen whether Australia’s forests are a harbinger for other tropical regions, but the implications for climate models are significant.

Professor David Karoly of the University of Melbourne called the study “the first time that this tipping point of a switch from a carbon sink to a carbon source in tropical rainforests has been identified clearly, not just for one year but for 20 years.” He noted that global models often assume forests will continue to absorb carbon at stable rates, but shifts like these could mean climate projections underestimate future warming. Although the forests still play a role in soaking up CO2, their reduced capacity makes emissions cuts “a lot harder” and demands a faster transition away from fossil fuels.

Australia, one of the world’s largest per-capita polluters, has pledged to cut emissions by at least 62% compared to 2005 levels over the next decade. Yet the country continues to face global criticism for its reliance on fossil fuels, with one of its biggest gas projects allowed to operate for another 40 years.

Dr. Raphael Trouve of the University of Melbourne, who was not involved in the research, said the study demonstrates the importance of maintaining long-term datasets to measure environmental change. “We thought the forest would be able to store more carbon because [CO2] is increasing,” he said. “But looking at these long-term empirical datasets, we find that is not the case, it allows us to confront the theory with reality and better understand how these systems work.”

“These findings challenge our future reliance on forests as natural absorbers of excess atmospheric carbon.”