Comparing approaches for carbon dioxide removal Author links open overlay panelNiallMac Dowell1R

[Andrew Lockley]

https://www.sciencedirect.com/science/article/pii/S2542435122004573

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Greenhouse gas removals—old news repackaged

Alternatively known as greenhouse gas removal (GGR), carbon dioxide removal (CDR), or negative emissions technology (NET), the concept of removing greenhouse gases (GHGs)—primarily CO2—from the atmosphere has been gaining increasing academic, industrial, financial, and political attention over recent years as corporate and national commitments to net-zero targets proliferate. Practically all pathways to net zero include essential contributions from NET, typically 10%–20% of current national emissions.

However, removing CO2 from the atmosphere is a much more established concept than one might think. The concepts of bioenergy with carbon capture and storage (BECCS)1 and CO2 disposal in carbonate minerals—the precursor to what is today referred to as “enhanced weathering” (EW)—have both been actively discussed since the mid-1990s.2 Direct air capture (DAC) was proposed from the late 1990s.3 The potential for including negative emissions as part of an emissions trading scheme (ETS) was first suggested over 20 years ago,4 but there has been little practical, legislative, or regulatory progress to date.

When these pathways for removing CO2 from the atmosphere were first proposed, their purpose was to manage atmospheric CO2 concentrations without needing to limit access to fossil energy. At this time, modern renewable energy was not nearly as developed as it is today. Although Article 2 of the 1992 UN Framework Convention on Climate Change calls for stabilizing GHG concentrations to avoid “dangerous anthropogenic interference” with the climate system, the 1997 Kyoto Protocol focused entirely on emissions rates. Whereas the former implies a transition to net zero at some point, the latter does not.

This paradigm shifted rapidly in the 2000’s. In 2008, the UK committed to an 80% reduction in economy-wide remissions—an unprecedented commitment at that time. However, even then the “need” for “at scale” deployment of CDR was unclear. Much of the required mitigation could be achieved via the (relatively) conventional approaches of energy efficiency, fuel switching, increased use of non-fossil energy sources, and carbon capture and storage (CCS). BECCS was included as a theoretical modeling construct as it was deemed the most carbon-efficient use of finite biomass resources, freeing up space to leave difficult emissions elsewhere in the economy. At this time, CDR—mostly in the form of BECCS—had made its way into various integrated assessment models (IAMs), and was not, initially, overly scrutinized. However, as time went on, observations regarding the impracticability of various model outcomes became more common, leading to increased emphasis on alternative pathways to the removal of GHGs from the atmosphere.

It was not until the 2015 Paris Agreement, and the subsequent special report by the IPCC on 1.5°C, that the need for the at-scale deployment of CDR was crystalized. To put “at scale” in context, today, total anthropogenic emissions are on the order of 50 GtCO2,e per year. By 2100, total global CDR is anticipated to be on the order of 10–20 GtCO2,e per year. In other words, the CO2 removal industry has the potential to grow to a scale that is comparable to the contemporary fossil fuel industry