Abby L. Harvey
GHG Monitor
8/7/2015
Carbon capture and storage alone will not be enough to keep global temperatures from exceeding the internationally recognized 2-degree Celsius limit, according to a study published this week in the journal Nature Communications. ”We find that negative emissions are required at significant levels (that is, 41 [gigatonnes of carbon] per year) to meet the 2-C target, even for very aggressive mitigation floors. Given that negative emission technologies—both on-site capture and atmospheric removal—are still at an early stage of development, this pleads in favour of developing (financial) mechanisms to put them on a technological learning trajectory,” the study says.
The researchers found that even in a best-case scenario “negative emissions of 0.5–3 Gt C (gigatonnes of carbon) per year and storage capacity of 50–250 Gt C are required,” according to the study. In the worst-case scenario, “those requirements are 7–11 Gt C per year and 1,000–1,600 Gt C, respectively.”
The researchers, led by Thomas Gasser, from the Institut Pierre-Simon Laplace in France, based their findings on a model designed to calculate emissions reduction needs. “The ultimate product of our study is an abacus where one can make assumptions on future conventional mitigation and read the negative emission requirements—and associated uncertainty—compatible with maintaining global warming below 2 C, as estimated by state-of-the-art [Earth system models]. Our results suggest that negative emissions are needed even in the case of very high mitigation rates, but also that negative emissions alone cannot ensure meeting the 2-C target.”
The model takes into account three variables. “First, we take fossil CO2 emission trajectories estimated to be compatible with this scenario using Earth system models (ESMs). Second, we make assumptions about maximum feasible pathways of conventional mitigation, covering a wide range of possible futures. Third, calculating the mass balance for each of these pathways we deduce the gross negative emissions needed to be compatible with the [representative concentration pathway] 2.6 scenario,” according to the study.
