For instructors who include a module on climate geoengineering, an excellent short reading on carbon dioxide removal approaches, and the challenges of effectively implementing them, is an article (subscription required) from last year by Sabine Fuss, et al., in the journal Nature Climate Change. As Fuss, et al. note, most emissions pathway scenarios that lead to atmospheric CO2 concentrations consistent with avoidance of temperatures above 2°C from pre-industrial levels contemplate some use of global net negative approaches in the second half of this century. In this study, the authors assess the prospects for the so-called “negative emissions” option most highly touted by the Intergovernmental Panel on Climate Change in its Fifth Assessment Report, Bioenergy with Carbon Capture and Storage (BECCS).
Among the findings of the authors are the following:

1. Many integrated assessment models (IAMs) contemplate carbon dioxide absorption by BECCS of 1,000 GtCO2 or more; this could effectively double the globe’s carbon “budget;”
2. Global net negative emissions strategies would have to be in place by 2070 for the most aggressive emissions scenarios. If deployment is delayed until substantial climate change has occurred, the response of the global carbon cycle will necessitate a larger program. Thus “the future option space depends strongly on today’s decisions;”
3. Challenges for deployment of BECCS include physical constraints associated with alternative land biomass and biomass needs (including agricultural demands and biodiversity conservation), response of terrestrial and ocean sinks to negative emissions, costs of speculative technologies and socio-institutional barriers, including public acceptance of new technologies;
4. In IAM scenarios consistent with keeping temperatures below 2°C from pre-industrial levels, BECCS approaches would have to sequester between 2-10 GtCO2 by 2050 (about 5-25% of 2010 CO2 emissions), and 4-22% of 2050 baseline emissions, which would entail “huge upscaling efforts,” especially in light of the currently challenging environment to develop large-scale CCS projects. This challenge is particularly imposing given the high costs of such projects and the low cost of emissions that are likely to be perpetuated absent the imposition of a meaningful price on carbon through climate policies;
5. While negative emissions options are, ostensibly, more expensive than other mitigation options, in the longer term, alternative mitigation pathways to 2100 are all substantially more costly without use of such technologies;
6. BECCS could serve as an alternative in the absence of a global accord to substantially reduce emissions for those countries lacking either capacity or the will to participate in international regimes.

Among the discussion questions that this piece might suggest:

1. How would we (can we?) reconcile the trade-offs between food production and energy production that, as the article suggests, BECCS might pose?;
2. While the article focuses on the viability of CO2 sequestration, what are the challenges, if any, of transport and storage of 2-10 GtCO2 annually?;
3. Are there tradeooffs associated with devoting substantial amounts of research and development funding to carbon dioxide programs? If yes, how does society, assess such trade-offs?