A new UN report suggests that the world needs a Plan B on climate change because politicians are failing to reduce carbon emissions.
It warns governments if they overshoot their short-term carbon targets they will have to cut CO2 even faster in the second half of the century to keep climate change manageable, the BBC reported.
If they fail again, they will have to suck CO2 out of the atmosphere.
This could be achieved by burning wood and capturing the CO2 emissions. The gas could then be stored in rocks underground.
But a leaked draft of the UN report also says that the technology for carbon dioxide removal is untested at such a scale.
The authors warn that carbon removal systems may encounter resistance from the public - and if the policy goes wrong, it could damage forests and ecosystems.
The final draft report to the Intergovernmental Panel on Climate Change (IPCC) adopts a new tone of realism in the face of repeated failures by governments to meet their rhetoric on climate change with action.
It warns that governments are set to crash through the global CO2 safety threshold by 2030. Humans have tripled CO2 emissions since 1970, it says - and emissions have been accelerating rather than slowing.
The experts advise governments that it will be cheaper overall to cut the greenhouse gas before 2030 if they want to hold emissions at 430-480ppm CO2 - a level that's calculated to bring a 66 percent chance of staying within a desired 2C threshold of warming by the end of the century.
