Planting a forest the size of the US could stop climate change - study
Planting an area the size of the US with trees would be the most effective way to combat change, according to a study published in the journal Science.
Researchers from the Crowther Lab in Switzerland say their analysis suggests there is the potential for 2.2 billion acres of tree cover in areas that would naturally support woodlands and forests.
As they grew and matured, the trees could absorb and store 205 billion tonnes of carbon.
If that mostly came from the atmosphere, it could tackle around two-thirds of the 300 billion extra tonnes of carbon which are in the atmosphere as a result of human activity since the industrial revolution.
The UK could play its part - the research estimates 11.37 million acres of tree cover could be created, much of it on grazing land which could continue to support livestock while providing carbon storage.
Professor Tom Crowther, senior author of the study, said: "We all knew restoring forests could play a part in tackling climate change, but we had no scientific understanding of what impact this could make.
"Our study shows clearly that forest restoration is the best climate change solution available today and it provides hard evidence to justify investment.
"However, it will take decades for new forests to mature and achieve this potential.
"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 in order to avoid dangerous climate change."
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The analysis used almost 80,000 high resolution satellite images of protected areas to assess natural levels of tree cover in areas ranging from Arctic tundra to savanna, open woods and dense forests.
In Google Earth Engine, they then used machine learning to determine tree cover in each area and map the potential coverage of trees across the world in the absence of human activity.
Much of the land that would be suitable for trees is used for cities and agriculture, needed to support a growing population.
However, some climate change scientists believe the conclusions drawn by the study are too optimistic.
Prof Simon Lewis, from University College London, said the estimate the extra forests could store 200 billion tonnes of carbon was "too high".
"New forests can play a role in mopping up some residual carbon emissions, but the only way to stabilise the climate is for greenhouse gas emissions to reach net zero, which means dramatic cuts in emissions from fossil fuels and deforestation," he said.
Prof Myles Allen, from the University of Oxford, said: "The additional 200 billion tonnes of carbon the study highlights represents less than one-third of human-induced carbon dioxide emissions to date, and less than 20 years of emissions at the current rate."
"Heroic reforestation" could help, he said, but there was no "nature-based solution" to ongoing fossil fuel use.
