Now researchers say the best solution is also the simplest: plant more forests. "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 unsafe climate change".
The total land, including current forested areas, that can support new trees.
Study author Thomas Crowther says this is the cheapest and best climate change solution.
Planting trees in these regions would increase Earth's forest-covered land by a third, all without affecting land humans use for cities and agriculture.
After recently publishing the most negative "OMG we're stuffed" post about climate change ever, it is a pleasure to write that we really can cure this, with carbon capture and storage - in trees.
"This is by far - by thousands of times - the cheapest climate change solution", study co-author Thomas Crowther, a climate change ecologist at the Swiss Federal Institute of Technology in Zurich, told The Associated Press.
Before his research, Crowther figured there were other more effective ways to fight climate change besides cutting emissions, such as people switching from eating meat to vegetarianism. 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.
That's roughly one trillion to 1.5 trillion new trees across an area the size of the entire United States, the team estimates. (Trees take carbon dioxide from the atmosphere and use it in a process called photosynthesis, which allows them to grow, ultimately storing that carbon in their leaves and other parts.) Russian Federation has the most space at 583,000 square miles (1.5 million square km), followed by the United States at 397,700 square miles (1 million square km), the researchers found.
Forests could be regrown on 1.7 billion-1.8 billion hectares of denuded areas that are no longer in use, adding 1.4 billion hectares if cropland and urban areas were included, it said. Trees remove more carbon from the air when they are younger, the study authors said. The study's lead author, Jean-Francois Bastin, estimated there's space for at least 1 trillion more trees, and potentially 1.5 trillion, AP reports, on top of the estimated 3 trillion trees now on the planet.
However, not everyone was as effusive about the new study.
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. "You can grow trees yourself, donate to forest restoration organizations or just invest your money responsibly in businesses which are taking action on climate change". "This one is not only our most powerful solution - it's one that every single one of us can get involved with".
The researchers, aided by hundreds of helpers, measured the amount of the tree cover shown in 80,000 high-resolution satellite images from Google Earth. "A hugely important blueprint for governments and private sector".
The Paris Agreement, which was first signed in 2015, is an worldwide agreement to control and limit climate change.
"None of this works without emissions cuts", he said. The problem is "related to the way we are living on the planet", he says.
Researchers analyzed tree cover in protected forest areas largely unaffected by human activity across the Earth's ecosystems, from arctic tundra to equatorial rainforest, studying almost 80,000 high resolution satellite photographs. Brazil and China are also on the list, and together those six countries contain 50 per cent of the area where forests could grow again.
They used three well-known climate models to update changes to the variables in order to project tree cover capacity for 2050.