“Determining the carbon sequestration potential of lands and land uses is a raging debate,” said Rob Jackson, Earth System Science professor at Stanford University.

This report, however, attempts to put a number on the amount of land this practice might require.

Around 1.2 billion hectares of land would have to earmarked for carbon dioxide removal to fulfil countries’ climate pledges – an area larger than the United States or almost four times the size of India, according to the authors.

“Countries treat land like a limitless resource in their climate plans,” said Kate Dooley, lead author and a researcher at the University of Melbourne.

“Using a land area equivalent to half of current global croplands for tree planting simply won’t work.”

The focus should be on stopping deforestation of standing forests rather than planting monocultures of new trees which can be more susceptible to fires and draught on land that could be used for food, the Land Gap report authors said.

Dooley said that restoring existing degraded forests, rangelands and farmlands of around 551 million hectares would be a reasonable target.

“Natural climate solutions are important but probably can’t offset more than a quarter of annual global fossil emissions of around 40 gigatonnes of CO2 equivalent,” Jackson said.

The criticism is not just levelled at countries but also companies.

“Corporations are currently pushing for scale in the voluntary carbon markets to service claims of carbon neutrality, but no one is doing the math on what is actually possible,” said co-author Jens Friis Lund of the University of Copenhagen.