Greenhouse gas emissions caused by damage to tropical rainforests around the world are being underestimated by a factor of six, according to a new study.
Research led by the University of Queensland finds the climate impact of selective logging, outright clearing and fire in tropical rainforests between 2000 and 2013 was underestimated by 6.53bn tonnes of CO2.
The numbers are likely conservative, and also did not include emissions from other woodlands or the massive boreal forests in the high latitudes of the northern hemisphere.
Study co-author professor James Watson of the University of Queensland and the Wildlife Conservation Society said: “We have been treating forests as pretty one-dimensional, but we know degradation impacts carbon. The bottom line is that we knew the numbers would be big, but we were shocked at just how big.”
Watson said the numbers used for tropical rainforests were “conservative”, adding, “this is a carbon time bomb and policymakers have to get to grips with this”.
When countries declare greenhouse gas emissions from changes in forests, they do not account for the CO2 that forests would have continued to soak up for decades had they not been cleared or damaged. This is a measure known as “forgone removal”.
The study, published in the journal Science Advances, also accounted for those emissions up to the year 2050 – a timeframe relevant to the global Paris climate change agreement.
The study found 6.53bn tonnes of CO2 for foregone emissions and the impacts of other damage that wasn’t being counted.
In comparison, for the year to March 2019, Australia’s emissions are at 538.9m tonnes CO2e (carbon dioxide equivalent) – or 0.54bn tonnes of CO2e. Global emissions from burning coal in 2017 were 14.6bn tonnes of CO2.
“Frankly, inside the environment movement there has been a huge push to get a handle on coal-based emissions, and the role of transport and airplanes. That’s important, but the forgotten child has been forests and woodlands,” Watson said.
The study only counted emissions from tropical forests. In total, the world’s forests soaked up about 28% of human-caused emissions between 2007 and 2016, with tropical forests accounting for about half that absorption.
“We have only looked at tropical forests and we have not looked at woodlands,” Watson said. “We also don’t look at the boreal forests which are the biggest game in town. Those numbers would be staggering. This story would be seriously worse if we looked at the whole vegetation estate.
“From a policy point of view, this is a horror story, but it also points to a simple solution,” he said, adding that keeping forests intact and properly accounting for the benefits would put countries like Australia at a “massive competitive advantage”.
Lead author Sean Maxwell of University of Queensland said: “Usually only ‘pulse’ emissions are considered – these are emissions released the instant intact forest is destroyed. Our analysis considers all impacts such as the effects of selective logging, forgone carbon sequestration, expanding effects on the edges of forests and species extinction.”
Pep Canadell of CSIRO and the Global Carbon Project, who was not involved in the study, said the findings were highly relevant.
“This brings lots of pieces together to show that if our ultimate goal from conservation was climate change, then there are many more components that we are not taking into account in our carbon accounting,” he said. “These researchers are calling this out.
“I think the numbers [in the study] are reasonable. They have developed a framework where we can better include the long-term value of the conservation of forests for the sake of the climate.”