'Forest protection' schemes used by airlines to allow carbon-neutral flying are flawed, according to a report by Greenpeace.
The research suggested that the calculations used by Verra, a major US non-profit organisation, to work out carbon offsetting through some forest protection schemes can be erroneous.
Carried out by Greenpeace and The Guardian, the report examined 10 forest protection schemes administered by Verra, which oversees the carbon credit standard VCS (Verified Carbon Standard).
Verra strongly denies the claims.
Forest protection schemes that rely on predictions of deforestation that would have occurred without the Verra scheme in place are often flawed, the report said.
Greenpeace said in a statement this week: "Satellite analysis of tree cover loss in the projects’ reference regions, carried out by leading consultancy McKenzie Intelligence Services, found no evidence of deforestation in line with what had been predicted by the schemes.
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"The offsetting market may not be fit for purpose because projects calculate their climate benefit using what some experts viewed as simplistic methodologies that fail to account for the impact of markets and governments on deforestation."
Thales West, who has worked on similar schemes, told The Guardian that the methodologies “are not robust enough".
West said: "There is room for projects to generate credits that have no impact on the climate whatsoever."
Carbon offsets, generated by emissions reduction projects, such as tree planting or shifts to less polluting fuels, have struggled for years to gain credibility.
As climate action has become urgent, the market is expected to grow to as much as $50 billion (£36 billion) by 2030.
Verra denied the claims, saying in a statement of The Guardian’s piece: "The article exhibits clear bias, is riddled with substantive errors that betray ignorance about how carbon crediting works, and fails to acknowledge the role of such projects in channeling finance to save the world's rainforests.
"The article is a product of a collaboration between The Guardian and the Unearthed house organ of Greenpeace, which has made no secret of its opposition to carbon offset credits.
"As such, it should come as no surprise that the conclusions in the article seek to discredit carbon finance generally and the use of it to protect forests, both of which have been targets of Greenpeace for years."
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