An upcoming UN report suggests that unproven technologies to suck carbon out of the air might be a fix for climate change, according to a leaked draft obtained by the Guardian.

Scientists and government officials gather in Berlin this week ahead of Sunday's publication of the Intergovernmental Panel on Climate Change's third part of its series of blockbuster climate change reports, which deals with policies addressing the emissions that drive global warming.

But environmentalists criticised the report's inclusion of a controversial new technique that would involve burning biomass – trees, plant waste, or woodchips – to generate electricity, and then capturing the released carbon, pumping it into geological reservoirs underground.

Proponents of the technique – known as bio-energy with carbon capture and storage (BECCS) – suggest that regrown trees and crops might sequester additional carbon, making the technology "negative emission" because it might reduce the overall amount of carbon dioxide in the atmosphere.



It is part of broader group of geoengineering technologies to suck carbon dioxide out of the air – most of them experimental – that the IPCC is now forecasting may require "large-scale deployment" to keep global warming below rises of 2C.

But critics have warned that "negative emissions" claims about the technology aren't well-founded, since associated industrial agriculture and forestry activities cause heavy emissions and regrown tree plantations do not act as carbon sinks. They further warn that large-scale conversion of land for the technology could threaten the livelihoods of millions of people in developing countries in the same way that the drive for biofuels has been linked to land grabs and food price rises.

"The technology is the dangerous spawn of two very bad ideas: it brings together the false premises and injustices of the bio-energy debacle with the risky, costly and unproven notion that we can bury carbon dioxide out of sight. That hardly seems a hopeful formula for calming the climate crisis. Such techno-fix fantasies will be welcomed by oil companies because they distract attention from the obvious solution of cutting fossil fuel use," said Almuth Ernsting, co-director of bio-energy watchdog Biofuelwatch.

A paper released last week by US-based Partnership for Policy Integrity concludes that biomass-burning facilities produce more pollutants and carbon emissions per megawatt-hour than coal-burning.

Meanwhile, carbon capture and storage technologies remain expensive, may leak, and will be impossible to commercialise soon enough to make an impact on carbon reductions before 2050, experts say. At present most of the carbon dioxide captured from existing carbon-capture projects is being sold for "enhanced oil recovery", which extracts extra petroleum from fields already exploited by conventional methods.

The full UN draft report admits that "the potential costs and risks of BECCS are subject to considerable scientific uncertainty," and the most recent UN report on climate change impacts advised that such CO2 removal technologies "might invite complacency regarding mitigation efforts."

Observers have pointed out that one of the co-chairs of the UN report's drafting team, Prof Ottmar Edenhofer, has been a long-time advocate for the BECCS technology.

The report refers to the CO2 removal technologies as "negative emissions" instead of geoengineering, a label that certain proponents have been promoting to disassociate the technologies from criticisms of geoengineering.

Currently, the draft for policymakers makes no mention of solar geoengineering, an even more controversial method that involves spraying sulphate aerosols into the atmosphere to reflect the sun and cool the planet. But observers close to the process say that Russia has continued to push for high-profile mentions of the solar geoengineering approach right up to the latest drafts of the report.