Scientists have documented a dismal shift in Australia''s rainforests: Tree lifespans have halved in the last 35 years, and it appears to be caused by climate change on the ecosystems.
These arid carbon sinks can result in devastating effects on the planet, creating a feedback loop that is both caused by global warming and which then contributes to it.
The signs of the increased mortality rate date back to the 1980s, implying that Earth''s natural systems have been able to respond to fluctuate temperatures and atmosphere for longer than we imagined.
"It was a relief to see such a significant increase in tree mortality, nor was it a rise in the number of species and sites we examined," says a ecologist and lead author from the University of Oxford in the United Kingdom.
"A sustained doubling of mortality risk might result in a double that carbon was stored in trees twice as fast to the atmosphere."
Over 70,000 data points were collected from previous records to complete the study, with 24 different forest plots included. The oldest information from the study has come back to 1971, making it possible for the team to track tree fatalities over an extended period.
The rise in tropical tree mortality is the reason for the rising water stress attributed to global warming, according to researchers: Trees are dryer and more quickly.
The study authors compared the stress that rainforests have experienced to what''s been happening to the Great Barrier Reef, another delicately balanced ecosystem that is dealing with higher temperatures.
"Our most likely driver," says ecologist Yadvinder Malhi from the University of Oxford, is the increasing drying power of the atmosphere due to global warming.
"If that is the case, tropical forests may soon become carbon sources, and the challenge of limiting global warming much below 2C becomes both urgent and more challenging."
Other research suggests that a similar rate of tree death is observed in the Amazon rainforests, reducing the amount of carbon that the region is able to pull out of the atmosphere and store. Rather, these forests will begin contaminating the atmosphere, rather than removing it.
The latest study is particularly useful because it uses a large pool of data collected over years, allowing scientists to eliminate the fear of such busy and active ecosystems in order to detect these long-term trends.
More research across a similar length of time is required to better understand the challenges that the natural world is facing. As difficult as it is to work together research projects that last decades, more studies across a similar level of timescale are urgently required to understand the situation.
"Long-term analyses like this one are very rare and very important for studying forest changes in response to climate change," says ecologist Susan Laurance from James Cook University in Australia.
"This is because rainforest trees may have such long lives, and that tree death is not always immediate."
Nature has recently published the research.