Climate targets cannot be met by negative emission technologies

Technology should not be used to delay action on reducing emissions

NEGATIVE emission technologies cannot remove enough carbon from the atmosphere to meet the Paris climate goals, and we should instead focus on cutting emissions at source, a new report finds.

The European Academies’ Science Advisory Council (EASAC) has looked at how techniques to remove carbon dioxide from the atmosphere could be used to meet the target of limiting global temperature rise this century to less than 2^oC above pre-industrial levels, and pursue efforts to limit the temperature increase to 1.5^oC.

A previous analysis by the European Commission in 2014 concluded that NETs are not a viable near-term solution but they should still be investigated to assess their future potential.

The EASAC report, Negative emission technologies: What role in meeting Paris Agreement targets?, is an updated analysis based on recent peer-reviewed literature, with more detailed descriptions of the candidate technologies and their future potential.

The report states that NETs should not be relied upon later in the century to compensate for failure to mitigate emissions now. Not only do the NETs investigated in the report fail to reach the level of carbon removal predicted in some climate scenarios, the time taken between researching new technologies and successfully implementing them will take decades. If NETs are a viable solution to climate change, they could influence policy makers to focus on these rather than to prioritise the more urgent need to curb emissions.

Staying within the carbon budget

Climate change scenarios have been calculated by the Intergovernmental Panel on Climate Change (IPCC) and use the concept of a “carbon budget”. This is the total amount of CO₂ that can be added to the atmosphere without exceeding the target temperatures.

In 2014, the IPCC calculated that no more than 1,000 Gt of CO₂ (GtCO₂) can be emitted between 2011 and 2100 for a 66% chance (or better) of remaining below 2^oC of warming. More than a fifth of that carbon budget has already been used in the past five years, and to stay within the budget now requires an end to carbon emissions from fuel production, transport, and energy use by 2050. Some IPCC scenarios rely on NETs after 2050 to compensate for continued emissions, however these projections assume that the technologies are fully functional. The EASAC report assessed the different types of NETs used in climate change scenarios.

Afforestation and reforestation

Plants absorb CO₂ so offer a possible low-cost ‘technology’ for carbon removal. However, for plants to absorb between 1.1–3.3 Gt of carbon (GtC) per year, 20–60% of global arable land would be required for their growth, and this would compete with land for agriculture. Afforestation and reforestation have already taken place in parts of Europe and China and while they show potential for carbon storage, numerous challenges have also been identified.

It is possible that carbon stored in the soil could be released during planting. Also, nitrous oxide emissions from fertilisers would increase and would have adverse effects on biodiversity. A significant change in land use has the potential to cause increased photoevaporation, changes in cloud cover, and changes in how much sunlight is reflected from the Earth’s surface. The carbon captured in plants is also vulnerable to fires, pests, and diseases – all of which are likely to increase with climate change. Using forestation as a carbon sink also needs to consider current rates of deforestation and that this would need to be dramatically reduced.