First of all, why even ask this question? In a recent piece on climate change policy, Ezra Klein captured the zeitgeist on geoengineering with the heading: "geoengineering is nuts." For US politicians/regulators, even speaking of geoengineering presents large risks, and leaves one open to rebukes from liberals and conservatives alike.
This negative perception of geoengineering likely stems from the conflation of geoengineering with the field of Solar Radiation Management (SRM). Consider the three SRM techniques the Oxford Geoengineering Programme lists on its website:
- Albedo enhancement. Increasing the reflectiveness of clouds or the land surface so that more of the Sun’s heat is reflected back into space.
- Space reflectors. Blocking a small proportion of sunlight before it reaches the Earth.
- Stratospheric aerosols. Introducing small, reflective particles into the upper atmosphere to reflect some sunlight before it reaches the surface of the Earth.
Each of these interventions is:
- Highly untested and has a large potential for adverse unintended consequences
- Relatively inexpensive such that a single actor could unilaterally enact them
- Not directly targeted at reducing GHG levels in the atmosphere, but rather targeted at other pathways that affect the climate
Thinking only about SRM, I can't blame Ezra for proclaiming that geoengineering is nuts.
The problem, however, is that the technical definition of geoengineering proposed by the Oxford Geoengineering Programme also includes CDR under its umbrella:
"Geoengineering - the deliberate large-scale intervention in the Earth's natural systems to counteract climate changes."
Now consider a few of the CDR techniques listed on Oxford's website:
- Afforestation. Engaging in a global-scale tree planting effort.
- Biochar. 'Charring' biomass and burying it so that its carbon is locked up in the soil.
- Bio-energy with carbon capture and sequestration. Growing biomass, burning it to create energy and capturing and sequestering the carbon dioxide created in the process.
None of these CDR interventions fits into the untested/risky/unilateral/non-carbon-cycle categories like SRM interventions do. But as long as CDR is considered in the same discussion as SRM, it is likely to languish in political and research obscurity.
Removing CDR from the geoengineering umbrella
Geoengineering scholars Rob Bellamy et. al note that the current definition of geoengineering that includes both SRM and CDR is "ambiguous" and creates "an artificial choice between geoengineering proposals." Another geoengineering scholar, Clare Heyward, proposes to resolve these issues by getting rid of the term geoengineering altogether, and adopting the following map of responses to climate change:
In this redefinition, Solar Radiation Management (SRM) would replace today's conception of geoengineering. CDR would fall under a category that I call "carbon management." GHG emission mitigation strategies designed to prevent GHGs from going in to the atmosphere would be one side of the "carbon management" coin, CDR strategies designed to take carbon out of the atmosphere would be the other side of this coin.
Why redefining geoengineering is important
Climate change remains a real and ever increasing threat. Our society urgently needs as many reasonable, low-risk "carbon management" solutions to this problem as possible, and I think most would agree that planting trees, incentivizing carbon sequestering agricultural practices, and building biomass power plants with carbon capture are reasonable sounding options that we should consider alongside renewable energy, energy efficiency, and other GHG emission mitigation strategies in our fight against climate change. But we won't start considering these strategies as long as they are conflated with the risky and untested SRM interventions. And if/when we do start talking about governance and policy for SRM, the conversation will proceed much more effectively if we already have governance/policy for CDR in place.
Bottom line: It doesn't make sense to classify CDR under the same umbrella as SRM. Let's start classifying CDR along with GHG emission mitigation strategies under the "carbon management" definition instead, leaving SRM for its own conversation.
More interesting links for the conversation on CDR and geoengineering:
Update: This is a great visual from Ken Caldeira that helps further put this debate in context: