By Daniel J. McLaughlin
Trees can be an important weapon in tackling the climate crisis.
As part of photosynthesis, they absorb and store carbon dioxide (CO2), a greenhouse gas that contributes to global heating, before it has a chance to reach the upper atmosphere.
A new study has identified land, the size of the US and China combined, that could be used in a massive reforestation effort.
However, others warn that it is not quite simple as that.
The Fast Company's Adele Peters says that billions of new trees could help stop climate change, and she explains how we can get them.
She reports on a new study, which found that "a massive reforestation effort could be a huge weapon in the climate fight".
A new global map shows huge swaths of land that could potentially be recovered with forests that have disappeared. It identifies 1.7 billion hectares of land that could feasibly return to forest - greater than the total area of the US and China combined.
The study claims that it could "help capture as much as two-thirds of the carbon that humans have pumped into the atmosphere since the industrial revolution".
While Peters admits it is far from the only thing that needs to happen to tackle the climate crisis, she says the study shows how much it can help.
Tom Crowther, a professor of global ecosystem ecology at ETH Zurich and one of the authors of the study, said: "Our research shows that it should really be considered to be a top solution that must be prioritised."
However, in an article for Discover Magazine, Daniel Bastardo Blanco argues that "we can't just plant billions of trees to stop climate change".
He notes that tackling the climate crisis will require more than just plating trees - saying it is part of many strategies, rather than a silver bullet.
Blanco asks whether the challenge is feasible, noting that it would "take many decades before new forests would be mature enough to store large amounts of carbon".
He explains: "Every possible parcel of land identified would have to be fully covered by trees. This is unlikely, considering that countries will lose economic potential as land gets covered up - something politicians might not be keen on doing.
"Additionally, areas along international borders could present logistical challenges. Not to mention the cost of massive reforestation projects - a limitation not considered in the study."
To limit the rise of global heating to 1.5C by 2050, the Intergovernmental Panel on Climate Change (IPCC) said that an extra 1 billion hectares (2.4 billion acres) of trees would be needed.
In the UK, the Committee on Climate Change (CCC) advised that tree planting must double by 2020. They say that new forests would "lock up carbon", as well as helping to limit the more frequent floods expected with global heating.
Their report said that the government should increase tree planting from 9,000 hectares (22,239 acres) per year to 20,000 hectares by 2020 - and then triple it to 27,000 hectares by 2030. This would result in increasing the forest cover from 13 per cent of the UK to 19 per cent by 2050.