Australia's wet tropics no longer drawing down carbon

Rainforest trunks and branches have gone from net carbon absorbers to a carbon source. (PR IMAGE PHOTO)

Three generations of scientists have been returning to the same few patches of Australian tropical rainforest, jotting down what they see.

For 49 years all up, researchers have been recording how fast trees are growing and how many reaching maturity in the lush green foliage of far north Queensland.