Restoration of forests has long been seen as a potential measure to combat climate change. The latest special report by the Intergovernmental Panel on Climate Change suggests that an increase of 1 billion hectares of forest will be necessary to limit global warming to 1.5°C by 2050. What has so far been unclear, however, is how much of this tree cover might be actually possible in the existing conditions on the planet.
Now, researchers have quantified how much land around the world is available for reforestation, as well as the extent of carbon emissions these would prevent from being released into the atmosphere. Trees, which absorb carbon dioxide, are a natural sink for the gas emitted into the atmosphere. According to the US National Oceanic and Atmospheric Administration, trees absorb about 25% of the carbon dioxide released into the atmosphere by the burning of fossil fuels, while the oceans absorb another 25%. The half that remains in the atmosphere contributes to global warming.
How they worked it out
The study, by researchers with the Crowther Lab of ETH Zurich university, has been published in the journal Science. On the basis of nearly 80,000 images from around the world, they calculated that around 0.9 billion hectares of land would be suitable for reforestation. “We are trying to restore a trillion trees,” Thomas Crowther, co-author of the paper and founder of the Crowther Lab, told The Indian Express by email. If an area of 0.9 billion hectares is indeed reforested, the researchers calculated, it could ultimately capture two-thirds of human-made carbon emissions.
“One aspect was of particular importance to us as we did the calculations: we excluded cities or agricultural areas from the total restoration potential as these areas are needed for human life,” lead author Jean-François Bastin said in a statement.
Earth’s continuous tree cover is currently 2.8 billion hectares, and the researchers calculated that the land available could support 4.4 billion hectares, or an additional 1.6 billion hectares. Out of this, 0.9 billion hectares — an area the size of the US — fulfil the criterion of not being used by humans, according to the paper.
These new forests, once mature, could store 205 billion tonnes of carbon, the researchers calculated. That is about two-thirds of the 300 billion tonnes of carbon that has been released into the atmosphere as a result of human activity since the industrial age.
“But we must act quickly, as new forests will take decades to mature and achieve their full potential as a source of natural carbon storage,” Crowther said.
Where’s that land
In India, there is room for an estimated 9.93 million extra hectares of forest, Crowther told The Indian Express. India’s existing forest cover makes up 7,08,273 sq km (about 70.83 million hectares) and tree cover another 93,815 sq km (9.38 million hectares), according to the Environment and Forest Ministry’s ‘State of Forest Report 2017’.
The study found that the six countries with the greatest reforestation potential are Russia (151 million hectares); the US (103 million hectares); Canada (78.4 million hectares); Australia (58 million hectares); Brazil (49.7 million hectares); and China (40.2 million hectares).
In a post on the website of Legal Planet, a joint initiative of University of California’s Berkeley and Los Angeles law faculties, Jesse Reynolds of UCLA described the new research as “misleading, if not false, as well as potentially dangerous”.
Among various arguments, Reynolds noted that the authors do not consider how such reforestation might come about when the land proposed to be reforested is owned and managed by many private persons, companies, nongovernmental organisations, and governments. Reynolds also found the authors’ estimate of carbon removal per area “remarkably high”.
He said the research will likely be used to “argue that we can rely more on reforestation to reduce climate change, potentially displacing efforts toward other responses [including] emission cuts”.