Negative Emissions Technologies and Direct Air Capture

AuthorTracy Hester
Pages749-771
Page 749
I. Introduction
Deep decarbonization wil l require a fundamental trans-
formation of U.S. energy and manufacturing industries,
but those sweeping changes alone wil l likely not suce.
Anthropogenic emissions since the star t of the Industrial
Revolution have already resulted in concentrations of car-
bon dioxide (CO2) in the ambient atmosphere that will lea d
to disruptive average global surface temperature increases
before the end of this century. Simply put, even if current
anthropogenic emissions drop to zero, the levels of CO2
already present in the atmosphere will have locked us into
rapid and intractable warming.1 Deep decarbonization of
future emissions also wi ll not suciently oset or respond
to damaging physical transitions caused by ongoing cli-
mate change that could cause substantial new greenhouse
gas (GHG) emissions, such as melting permafrost, reduced
arctic albedo, and carbon releases from forest res.2
1. I P  C C (IPCC), C
C 2014: S R §2.4, at 63 (2014) (“[w]arming caused
by CO2 emissions is eectively irreversible over multi-century timescales
unless measures are taken to remove CO2 from the atmosphere”).
2. Id. §2.2.4, at 62.
To address CO2 concentrations already stockpiled in the
atmosphere, deep decarbonization will li kely require addi-
tional steps beyond simply halting carbon emissions from
ongoing economic activities. One potential option under
active investigation is ambient CO2 removal t hrough t he
deployment of negative emissions technologies (NETs),
including the direct air c apture (DAC) of atmospheric CO2
or other GHGs to sequester them in an inaccessible or inert
form or convert them into a commercial product or good.3
Given the enormous challenges facing eort s to adequately
reduce current GHG emissions, climate change forecasts
and strategies have begun to devote growing attention to
NETs as a complement to broad emissions mitigation.4 For
3. E A S A C, EASAC P R-
 N. 35, N E T: W R  M-
 P A T (2018); James Hansen et al., Young People’s
Burden: Requirement of Negative CO2 Emissions, 8 E S. D
577-616 (2017), https://doi.org/10.5194/esd-8-577-2017. Some research-
ers, it should be noted, believe that the Paris Agreement’s 1.5°C target can
still be attained without relying on NETs, but this approach would require
aggressive decarbonization of energy sources and drastic reductions in en-
ergy usage. Elmar Kreigler et al., Pathways Limiting Warming to 1.5° C: A
Tale of Turning Around in No Time?, 376 P. T. R. S. A 20160457,
https://doi.org/10.1098/rsta.2016.0457 (2018).
4. Robert B. Jackson et al., Focus on Negative Emissions, 12 E. R. L-
 110201 (2017).
Chapter 29
Negative Emissions Technologies and
Direct Air Capture
by Tracy Hester
Summary
Given the U.S. economy’s continuing reliance on fossil fuel energy sources and the high levels of anthropogenic
greenhouse gases already in the atmosphere, a full deep decarbonization pathway assessment will have to explore
the use of negative emissions technologies (NETs), which include the direct air capture of ambient CO2. NETs
are technologies that capture or consume more CO2 than they emit on a cumulative basis, and direct air cap-
ture, loosely dened, is a subset of NETs that use any industrialized chemical or physical methods to remove
greenhouse gases from the ambient atmosphere and then store or reuse those gases typically in a way that does
not allow them to escape back into the atmosphere. While still nascent, NETs include a wide array of approaches
such as biomass energy with carbon capture and sequestration, enhanced weathering of minerals, and the direct
mechanical capture of ambient CO2 through lters and chemicals. is chapter focuses on the legal pathways
needed to accelerate the development and use of NETs and assure their proper governance.
Page 750 Legal Pathways to Deep Decarbonization in the United States
example, the United Nations Intergovernmental Panel on
Climate Change’s (IPCC’s) latest integrated assessment
models suite of 900 scenarios found only a small set of 76
pathways that could attain the Paris Agreement’s target of
limiting temperature increases to 2 degrees Celsius (°C)
or less, and the vast majority of those models relied on
NE Ts. 5 In particula r, the models assume that the world
community will broadly adopt the technology of generat-
ing power through burning biomass for energy w ith car-
bon capture and sequestration (BECCS) of the resulting
emissions.6 More recent assessments have emphasized that
the Paris Agreement’s ambitious 1.5°C target will virtually
require broad use of NETs, while the original 2°C target
allows more exibility for a gradual or reduced deployment
of NE Ts.7
While most of this book focuses on approaches to
remove carbon from the production of energy and eco-
nomic goods, this chapter assesses the legal and policy
challenges of decarboni zing the atmosphere itself through
NETs and, in particular, DAC. e Deep Decarboniza-
tion Pathways Project’s (DDPP’s) analysis does not discuss
the viability and impact of th is potential approach because
it concluded that the feasibility and sustainability of large-
scale NETs, including DAC, remained too uncertain at
that time to include in country-level deep decarboniz a-
tion pathw ays.8 For example, in its 2014 interim report,
the DDPP excluded from its pathway assessments any
signicant reductions achieved by NETs. According to
the DDPP, “[t]he sustainability of the large-scale deploy-
ment of some net negative emissions technologies, such as
BECCS, raises issues still under debate, in part due to the
5. Kevin Anderson & Glen Peters, e Trouble With Negative Emissions, 354
S 182 (2016) (“[i]t is not well understood by policy-makers, or in-
deed many academics, that [integrated assessment models showing attain-
ment of the Paris Agreement’s 2°C goal] assume such a massive deployment
of negative-emission technologies,” including assumptions that NETs will
bring global emissions to at least net zero in the second half of the 21st cen-
tury); J B. H  ., H P  C A-
, I   P A  C D R-
  S G 3 (2016). See also M G,
C/SIPA C  G E P, W  P
A M L  F F 2 (2015) (concluding that
the Paris Agreement will require capture of carbon emissions before they
enter the air, create new sinks, and “[d]evise, and deploy on a massive scale,
technologies to remove the carbon from the air, and sequester it”).
6. Anderson & Peters, supra note 5, at 183.
7. J Minx et al., Negative Emissions—Part 1: Research Landscape and Synthesis, 13
E. R. Lers 063001, at 13 (2018), https://doi.org/10.1088/1748-
9326/aabf9b (“In fact, 2°C scenarios do not fundamentally depend on
negative emissions at large scale.”)
8. S D S N  I  S-
 D  I R, P 
D D: 2014 R 8-9 (2014) [hereinafter P-
 R] (“We have therefore made an assumption in the DDPP that
large-scale net negative emissions are still too uncertain to build into our
country-level Deep Decarbonization Pathways (DDPs), even though we
strongly support research programs that could make net negative emissions
a future reality”); id. at 19 (“A disadvantage is that the process of isolating
and removing the CO2 from air at low ambient concentrations is technically
challenging, currently expensive, and unproven at scale.”)
competition in land uses for energy and food purpose s.”9
e DDPP’s nal report did not rely on NETs or DAC for
similar reasons.10
Yet, despite its current technological uncertainty, the
potential broad use of NETs could oer signicant ben-
ets to the deep decarbonization initiative. As the DDPP’s
authors note, the availability of NETs such as BECCS or
DAC would enable a gentler transition to a low-carbon
economy because they would allow for a higher CO2 bud-
get in the rst half of the 21st century to the extent that
those NETs become widely available in the second half
of the century.11 More importantly, the widespread use of
NETs could help reduce the historical accumulations of
atmospheric GHGs that would currently result in poten-
tially disruptive climate change even if ongoing emissions
dropped to zero. While we now have only an initial sense
of the technological eciency and economic viability of
NETs, some early assessments foresee that the wide use of
NETs and DAC in the United States alone could lead to
a removal of approximately 13 gigatons (Gt) of CO2 per
year with a cumulative removal of approximately 1,100 Gt
CO2 by 210 0.12 In the United Kingdom (U.K.), land-based
NETs could potentially remove 12 to 49 megatons (Mt) of
carbon equivalent annually, or about 8% to 32% of cur-
rent emissions.13 By comparison, anthropogenic emissions
of CO2 equiva lent (CO2e) emissions reached a rate or 49
+4.5 Gt per year.14 A clearer legal framework that removes
potential regulatory and liability barriers, as well as poli-
cies that foster and support the actua l implementation of
NETs, could encourage their broader deployment at scale
in a speedier time frame.
e widespread deployment of NET strategies to achieve
deep decarbonization would need to surmount several leg al
hurdles. Given the potentially important role that ful ly
developed NETs could play in reducing CO2 levels in the
ambient atmosphere, the removal of these legal obstacles at
an early stage could play an important role in improving
the odds for their availability a s a policy option.15 For clar-
9. S D S N  I  S-
 D  I R, P 
D D I R 2 (2014), http://www.iddri.org/
Publications/Rapports-and-brieng-papers/DDPP%20Executive%20Sum-
maryEN.pdf.
10. P R, supra note 8, at 8-9, 19.
11. Id. at 18-19.
12. N R C   N A, C
I: C D R  R S
62 (2015) [hereinafter NAS R].
13. Pete Smith et al., Preliminary Assessment of the Potential for, and Limitations
to, Terrestrial Negative Emission Technologies in the UK, 18 E. S.: P-
  I 1400 (2016).
14. C C 2014: S R,  F A R-
   I P  C C 5 (2015),
available at https://www.ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_
FINAL_full_wcover.pdf.
15. While this chapter focuses on the legal issues related to NETs and DAC
under U.S. environmental laws, other nations and international organiza-
tions have begun to actively explore the same issues. For example, the Eu-

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