Negative greenhouse gas emissions: Assessments of feasibility, potential effectiveness, costs and risks

10-06-2015

The negotiating text for the new international climate agreement contains several references to 'net-zero' carbon emissions. This level of emissions is to be achieved some time in the second half of this century to avoid the dangerous levels of global warming that would result from high greenhouse gas concentrations in the atmosphere. Since some carbon emissions cannot be avoided completely (for example in agriculture, aviation and iron production), carbon dioxide (CO2) would have to be removed from the air, resulting in 'negative emissions' that compensate for the remaining emissions. Negative emissions may also be needed to reduce atmospheric greenhouse gas concentrations if safe limits are exceeded. Most of the climate stabilisation scenarios of the Intergovernmental Panel on Climate Change assume the use of negative emission technologies. Recent reports by Oxford University and the US National Academy of Sciences assess available and emerging negative emission technologies, along with their benefits and risks. The reports agree that negative emission technologies are not a substitute for substantial cuts in emissions, but they are expected to play an important role in climate stabilisation by compensating for the remaining emissions. The cheapest and least risky approaches in the short to medium term are forestation and soil carbon enhancement. Bioenergy with carbon capture and storage may play a big role later in this century. Other technologies are still considered too expensive, risky and energy-intensive. Questions of financing and governance remain unresolved.

The negotiating text for the new international climate agreement contains several references to 'net-zero' carbon emissions. This level of emissions is to be achieved some time in the second half of this century to avoid the dangerous levels of global warming that would result from high greenhouse gas concentrations in the atmosphere. Since some carbon emissions cannot be avoided completely (for example in agriculture, aviation and iron production), carbon dioxide (CO2) would have to be removed from the air, resulting in 'negative emissions' that compensate for the remaining emissions. Negative emissions may also be needed to reduce atmospheric greenhouse gas concentrations if safe limits are exceeded. Most of the climate stabilisation scenarios of the Intergovernmental Panel on Climate Change assume the use of negative emission technologies. Recent reports by Oxford University and the US National Academy of Sciences assess available and emerging negative emission technologies, along with their benefits and risks. The reports agree that negative emission technologies are not a substitute for substantial cuts in emissions, but they are expected to play an important role in climate stabilisation by compensating for the remaining emissions. The cheapest and least risky approaches in the short to medium term are forestation and soil carbon enhancement. Bioenergy with carbon capture and storage may play a big role later in this century. Other technologies are still considered too expensive, risky and energy-intensive. Questions of financing and governance remain unresolved.