A commonly cited statistic during the lead-up to the signing of the 2015 Paris Agreement has come to be known as the “2-degree guardrail.” This term is a nod to the idea that if the combined emissions-mitigation efforts of the world’s nations could succeed in keeping global temperatures from rising 2°C above preindustrial levels, the human race might avoid inflicting lasting, and perhaps irreparable, damage on Earth’s environment.
However, although 197 countries signed off on the agreement, each pledging to reduce emissions, most scientific experts agree it will not be enough. Even if every country meets its goals, a large‐scale removal of carbon dioxide from the atmosphere will likely be necessary to offset greenhouse gas emissions, which are notoriously difficult to mitigate. And for every country that fails to meet its own emissions goal, this carbon dioxide removal effort would need to be all the more gargantuan.
Here Boysen et al. consider a type of terrestrial carbon dioxide removal project involving the construction of highly managed massive farms, or biomass plantations, with the purpose of capturing and storing carbon. Many mitigation scenarios assume this kind of project to be economically feasible and promote the use of green, nonfossil fuels.
However, the researchers found that it would be all but impossible to sufficiently counteract estimated emissions levels with such a project: The plantations would need to be so extensive that they would overtake all the livable land and natural ecosystems on Earth. Even if sizable emissions cuts take place, it would be impractical; to be effective, the proposed project would need to use more than two thirds of today’s farmland or one third of global forest area. Needless to say, this land use would seriously affect humans’ ability to grow food as well as basic planetary functions. On the contrary, intense irrigation, substantial fertilizer application, and high-tech carbon-processing facilities would be vital to fulfill the required levels of carbon dioxide extraction considered by many mitigation scenarios that include such social and economic constraints.
The study makes plain that relying solely on biomass plantations would not be a viable alternative to the near-future emissions reduction strategy put forth by the Paris Agreement. But that’s not to say we should rule out such terrestrial carbon dioxide removal altogether. In conjunction with other techniques and in well-selected places, the researchers say, it could be a strong component of future mitigation plans. (Earth’s Future, https://doi.org/10.1002/2016EF000469, 2017)
—Sarah Witman, Freelance Writer