"It is vitally important that we protect the forests that exist today, pursue other climate solutions, and continue to phase out fossil fuels from our economies".
"This is by far - by thousands of times - the cheapest climate change solution" and the most effective, said study co-author Thomas Crowther, a climate change ecologist at the Swiss Federal Institute of Technology in Zurich. Even with existing cities and farmland, there's enough space for new trees to cover 9 million square kilometres, they reported in yesterday's journal Science. The potential for removing the most carbon is in the tropics.
"Restoration of trees may be "among the most effective strategies, ' but it is very far indeed from "the best climate change solution available, ' and a long way behind reducing fossil fuel emissions to net zero", said Myles Allen, a geosystem science professor at Oxford".
The study calculated that over the decades, those new trees could suck up almost 750 billion tonnes of heat-trapping carbon dioxide from the atmosphere.
The ETH Zurich researchers say six countries with the most space for new trees are Russian Federation, the United States, Canada, Australia, Brazil and China.
Also, if cropland and urban areas were included, the forests could be regrown on an additional 1.4 billion hectares of land, adding 0.7 billion hectares of tree canopy cover, according to the study.
In a first of its kind study, a team at ETH Zurich has calculated the potential area and impact of a new forest large enough to slash roughly two-thirds off the atmospheric carbon pool.
"But the question of whether it is actually feasible to restore this much forest is much more hard", Field said in an email.
"The restoration of ecosystems that could support trees is our main weapon to fight climate change", Jean-François Bastin, the study's lead author from ETH-Zürich, told us in an email. However, the study finds that over 43% of these countries have committed to restore less than half the area that can support new forests while 10% have committed to restoring considerably more land than is suitable for forest growth.
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And while the northern boreal forests in areas such as Siberia are expected to increase with climate change, dense tropical forests are likely to become less hospitable and could face losses that outweigh the possible gains. But a proposal that costs a tenth as much as carbon capture and geoengineering has to be given serious consideration. Individuals could make a tangible impact by growing trees themselves, donating to forest restoration organizations and avoiding irresponsible companies, he added.
Prof, Crowther added: "Although government action is essential to make the most of this opportunity, this is a climate solution we can all get involved in and make a tangible impact".
"Finally an authoritative assessment of how much land we can and should cover with trees without impinging on food production or living areas", she said in a statement.
"None of this works without emissions cuts", he said.
There are skeptics quoted in the Guardian who say that these calculations are not accurate, and of course we are actually losing forest to grazing and monoculture farming. This was made possible because of a unique global dataset of forest observations and the free mapping software of Google Earth Engine. They then used artificial intelligence computing to combine that data with 10 key soil, topography and climate factors to create a global map of where trees could grow.
The forests could be regrown on 1.7 to 1.8 billion hectares of land in areas that are not now used as urban or agricultural land, adding 0.9 billion hectares of tree canopy cover, according to the study.