In their latest study, researchers Jean-Francois Bastin and Tom Crowther of the Swiss Federal Institute of Technology in Zurich (ETH) have shown for the first time where in the world new trees could grow and how much carbon they would store.
The researchers are working in the Crowther Lab at ETH, where they are investigating nature-based solutions to climate change.
Study lead author Jean-François Bastin explains: “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.”
The researchers calculated that under the current climate conditions, Earth’s land could support 4.4 billion hectares of continuous tree cover. That is 1.6 billion more than the currently existing 2.8 billion hectares. Of these 1.6 billion hectares, 0.9 billion hectares fulfil the criterion of not being used by humans. This means that currently, an area of the size of the USA is available for tree restoration.
Once mature, these new forests could store 205 billion tonnes of carbon: 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 Revolution.
“We all knew that restoring forests could play a part in tackling climate change, but we didn’t really know how big the impact would be. Our study shows clearly that forest restoration is the best climate change solution available today,” says Professor Thomas Crowther, co-author of the study and founder of the Crowther Lab at ETH Zurich. “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.”
The study also shows which parts of the world are most suited to forest restoration. The greatest potential can be found in just six countries: Russia (151 million hectares), the USA (103 million hectares), Canada (78.4 million hectares), Australia (58 million hectares), Brazil (49.7 million hectares) and China (40.2 million hectares).
Many current climate models are wrong in expecting climate change to increase global tree cover, the study warns. It finds that there is likely to be an increase in the area of northern boreal forests in regions such as Siberia, but tree cover there averages only 30 to 40 per cent. These gains would be outweighed by the losses suffered in dense tropical forests, which typically have 90 to 100 per cent tree cover.
A tool on the Crowther Lab website enables users to look at any point on the globe, and find out how many trees could grow there and how much carbon they would store. It also offers lists of forest restoration organisations.
Link to study in the journal Science: