Two recent studies are offering new evidence that the carbon-sequestering forests required to hold average global warming to 1.5°C are in peril.
“The Earth saw nearly 260,000 square kilometres of lost tree cover last year—an area roughly the size of Colorado,” reports the Washington Post, citing a just-released satellite-based survey by Global Forest Watch. That figure is an overall increase of 7% from 2019.
The world’s tropical rainforests fared even worse: more than 41,500 square kilometres of these biodiverse and carbon rich ecosystems were lost in 2020, an increase of 12% over the year before.
The climate impact has been immediate and heavy. “All those felled trees in primary tropical forests contributed the equivalent of 2.6 billion tonnes of CO2 emissions to the atmosphere,” the Post writes.
Such a loss being recorded despite COVID restrictions is “shocking,” said Simon Lewis, a professor of global change science at University College London. But, the Post notes, while it is shocking, it is not surprising—given that the drivers of forest loss are a combination of climate feedbacks already in play and ongoing failures of key countries (think Bolsonaro’s Brazil) to implement and enforce forest protection measures.
In places like Australia, Russia, and the United States, last year’s forest loss was largely due to the pressures of drought, insect infestations, and ferocious wildfires—all largely a consequence of warmer winters.
“In the tropics, meanwhile, the key drivers were deliberately set fires that escaped their keepers and the expansion of agriculture,” the Post writes, adding that Brazil’s Amazon rainforest experienced the greatest losses.
All told, Brazil lost “a swath of old-growth forest in 2020 larger than the state of Connecticut.” Included in this measure is a “staggering” 30% loss of wetlands in the Pantanal. Vast stretches of peat-rich land burned in that region last year, “triggering intensive carbon emissions to the atmosphere.”
And 2020’s losses in the Amazon have global significance, the Post adds. While forests lost to wildfires and drought in more temperate regions stand some chance of growing back, such resilience is far less likely for much of the Brazilian rainforest, whose destruction is part of the economic calculus of a government determined to advance the fortunes of cattle ranchers and soy and palm oil producers.
And even if vegetation were permitted to return, some scientists fear that parts of the Amazon may be close to “tipping” into savanna, a transformation that would permanently lower the forest’s capacity to store carbon.
What is desperately needed, Lewis told the Post, is public policy geared to forest protection—as the improving situation in Indonesia has proven.
“What governments do matters,” he said. “Countries could get hold of deforestation rates and drive them down. It’s possible. It’s within our grasp.”
Confirming the key role that tropical forests will play in keeping global warming below the critical threshold of 1.5°C, Lewis flagged the particular need to figure out how to feed a still expanding global population without expanding the global footprint of agriculture—with reducing food waste and promoting plant-based diets as critical strategies.
And South America’s tropical rainforests aren’t the only ones in trouble. A study just published in Science Advances has found that the Ivory Coast, Guinea, and Ghana have lost respectively 71%, 67%, and 60% of their rainforest cover, a total of some 220 million hectares, reports SciDevNet.
Analyzing 30 years of satellite data, including 1.37 million images courtesy of cloud computing, the researchers discovered that 17% of forest losses in the area studied owe to agriculture and other land use changes.
Meanwhile,the University of Birmingham reports on a review just published in Nature Plants that reveals a dangerous lack of knowledge about the increasingly high mortality rates of the world’s biggest and oldest tropical trees.
Led by Adriane Esquivel-Muelbert, a lecturer at Birmingham, and Evan Gora, a Smithsonian Tropical Research Institute (STRI) fellow, the review of hundreds of research papers determined that “nearly nothing is known about the biggest trees and how they die because they are extremely rare in field surveys.”
That dearth of knowledge owes in large part to the sheer physical difficulty of measuring trees, said Esquivel-Muelbert. (It isn’t easy to carry a ladder through the jungle.) But, Gora added, skipping the study of trees above 50 centimetres in diameter effectively “leaves out half the forest biomass in most forests.”
Scientists theorize that the giants of the rainforest may be suffering greater mortality than their smaller kin because their height makes them more likely to be damaged by storms which, due to climate change, tend to bring much stronger winds and more lightning. And because big trees need to pull more water, they may be more vulnerable to drought.
To more fully ascertain why big tropical trees are dying, future researchers will need to ensure that big trees do get included in field surveys, that the geographical scope of large-tree studies is expanded beyond Latin America, and that studies focus more on other factors that can kill big trees (insects and disease, for example).
Speaking with the Washington Post about the Global Forest Watch study, Deborah Lawrence, a professor of environmental sciences at the University of Virginia, called tropical forests a “carbon sequestering machine”.
“We cannot lose that stock,” she said. “If we don’t lose them, we still have to work really, really hard [to cut global emissions]. If we do lose them, I don’t think we can make it.”