Carbon removal from atmosphere unavoidable for 1.5 degree target

Technologies that extract carbon dioxide (CO2) from the atmosphere will be needed to limit global warming to 1.5 degrees – the cornerstone of the Paris Agreement on Climate Change – but significant differences in their potential and risks are not being addressed by policy makers.

An international consortium of climate scientists, led by Prof Jan Minx, Priestley Chair in Climate Change and Public Policy, have undertaken three comprehensive studies of these “negative emissions technologies” (NETs), identifying a major gap between the science and policy.

With the exception of the USA, all countries in the world have committed to “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C”. However, technology development and expansion, as well as the start of pilot projects, are lagging behind deployment in climate mitigation scenarios.

Meeting the 1.5°C goal necessitates large scale dependence on negative emissions: 500-1000 Gt CO2 needs to be stored safely under the Earth’s crust (equivalent to 10- 25 years of today’s global emissions).

The good news, the scientists point out from their review, is that the extensive use of negative emission technologies can be reduced to a minimum or even zero to keep warming below 2°C.

Prof Minx is lead author of one of the studies, which were headed by the Mercator Research Institute on Global Commons and Climate Change (MCC) in Berlin. They were published in a special section of Environmental Research Letters on Tuesday 22 May 2018.

Max W Callaghan, PhD student at the School of Earth and Environment at the University of Leeds, was a co-author in all three studies and instrumental in building up the infrastructure for the systematic assessment of thousands of articles on negative emissions.

Science-policy gap

Underlining the gap between the state of the science and policy on negative emissions, the authors point out that the necessary deployment of NETs is rarely discussed in politics, despite the fact that some of these technologies involve considerable conflicts for land use, water consumption or energy requirements among others.

“Although policymakers like to set ever more ambitious targets in the climate negotiations, the concrete actions so far are lagging far behind. The result is a growing dependence on negative emissions,” says Jan Minx, head of the MCC Working Group on Applied Sustainability Science.

“There is an urgent need for the international community not to further increase but reduce its dependence on technologies for carbon removal from the atmosphere. To achieve this, we need to reduce greenhouse gas emissions much more rapidly”.

Negative emission technologies aim to remove carbon dioxide (CO2), the major driver of man-made climate change, from the atmosphere. They include relatively simple options like planting more trees to lock up CO2 as they grow, or crushing rocks that naturally absorb CO2 and spreading them on soils so that they remove CO2 more rapidly.

Other higher-tech options include using chemicals to sequester CO2 from the air, or burning plants for energy and capturing the CO2 that would otherwise be released, then storing it permanently deep below the ground (known as bioenergy with carbon capture and storage, or BECCS).

Big data methods

The three new studies represent the most comprehensive literature review to date. They  were prepared by an international consortium of 20 researchers at six institutes in different countries.

More than 6,000 documents were considered on seven groups of technologies: BECCS, afforestation and reforestation, direct air carbon capture and storage (DACCS), enhanced weathering, ocean fertilisation, biochar and carbon sequestration in soil. Using a systematic process and big data methods, 1000 studies were identified that provided relevant information on the potential, costs and side effects of the various technologies for CO2 removal.

According to the studies, all technologies have relevant potential, except ocean fertilization. However, they differ in terms of costs, side effects, development status and long-term storage potential: afforestation, for example, could already be carried out at large scale today, but the CO2 could be released more easily again by human or natural influence. BECCS could safely store large quantities of CO2, but the technology is still in the demonstration phase and faces opposition from the public.

Urgent upscaling

The researchers found that almost two-thirds of the literature focuses on the early phases of NET research and development, making it all the more important to research actual use and upscaling of new technologies.

“If negative emissions technologies are to be massively scaled up by mid-century in the way many IAM scenarios portray them, then the innovation literature implies that we should be seeing demonstrations, niche applications, and early adoption occurring imminently,” says co-author Greg Nemet of the University of Wisconsin-Madison, who led the review on NETs innovation and upscaling.

Sabine Fuss, Head of the MCC Working Group for Sustainable Resource Management and Global Change, emphasised the importance of research to support upscaling. “In order to clarify the opportunities and risks of negative emissions and to make them possible on an industrial scale, a roadmap for pilot projects must be developed.”

Negative emissions will likely feature prominently in the IPCC’s Special Report on Global Warming of 1.5°C, which will be published in the autumn.

Image: Andreas Habich – Own work, CC BY-SA 3.0