Australian Tropical Forests Switch from CO2 Absorber to Carbon Emitter in World First

Trees in Australia's tropical rainforests have become the first worldwide by transitioning from serving as a CO2 absorber to turning into a carbon emitter, due to increasingly extreme temperatures and arid environments.

The Tipping Point Identified

This significant change, which affects the trunks and branches of the trees but does not include the underground roots, began approximately 25 years ago, as per recent research.

Trees naturally store carbon during growth and emit it when they decompose. Generally, tropical forests are regarded as carbon sinks – taking in more carbon dioxide than they release – and this absorption is assumed to increase with higher CO2 levels.

However, nearly 50 years of data gathered from tropical forests across Queensland has shown that this essential carbon sink may be at risk.

Study Insights

Roughly 25 years ago, tree stems and limbs in these forests became a net emitter, with increased tree mortality and insufficient new growth, as the study indicates.

“It’s the first tropical forest of its kind to display this sign of change,” stated the principal researcher.

“It is understood that the moist tropics in Australia occupy a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it might serve as a future analog for what tropical forests will experience in global regions.”

Global Implications

A study contributor noted that it remains to be seen whether Australia’s tropical forests are a precursor for other tropical forests globally, and additional studies are needed.

But should that be the case, the results could have major consequences for international climate projections, CO2 accounting, and climate policies.

“This research is the initial instance that this tipping point of a transition from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not just for one year, but for two decades,” remarked an authority on climate science.

Worldwide, the share of carbon dioxide taken in by forests, trees, and plants has been relatively constant over the last 20 to 30 years, which was expected to persist under numerous projections and policies.

But if similar shifts – from sink to source – were detected in other rainforests, climate forecasts may underestimate global warming in the coming years. “This is concerning,” he added.

Continued Function

Although the balance between growth and decline had shifted, these forests were still playing an important role in soaking up CO2. But their diminished ability to absorb extra carbon would make emissions cuts “more challenging”, and require an accelerated transition away from fossil fuels.

Research Approach

The analysis utilized a distinct collection of forest data starting from 1971, including records tracking approximately 11,000 trees across 20 forest sites. It considered the carbon stored above ground, but not the gains and losses below ground.

An additional expert highlighted the importance of gathering and preserving extended datasets.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But looking at these decades of recorded information, we find that is incorrect – it enables researchers to compare models with actual data and better understand how these systems work.”