REFLECTIONS ON AIR CAPTURE: THE POLITICAL ECONOMY OF
ACTIVE INTERVENTION IN THE GLOBAL ENVIRONMENT
An Editorial Comment
When global climate change came onto domestic and international policy agendas
in the late 1980s, only two types of response were initially considered: reducing
emissions by improving efficiencies or switching to lower or non-carbon energy
sources; and adapting to the anticipated changes. Since that time the agenda of
potential responses has been progressively expanded, principally by adding various
ways to intervene in the global carbon cycle or the climate to break the connection
between emissions of greenhouse gases and the resultant climate changes.
1
Three
types of these “intervening” responses are now, to varying degrees, present in policy
debate: biological sequestration of carbon in forests or soils (Schlamadinger and
Marland, 2000); point-source carbon capture from fossil fuels or combustion gases,
followed by sequestration in stable reservoirs (Parson and Keith, 1997); and various
forms of albedo modification or other direct manipulation of the climate system,
collectively called geoengineering (Keith, 2000).
In this issue of Climatic Change, Keith, Ha-Duong, and Stolaroff (2006) propose
that one additional intervening option should be considered: capturing CO
2
directly
from the atmosphere, then sequestering it in the same reservoirs as would be used
for carbon captured from point sources. They argue that air capture, like a conven-
tional backstop energy technology, can provide an essentially unlimited quantity of
mitigation at constant, high marginal cost. But because air capture would be com-
pletely uncoupled from the energy system, it would have two key advantages over
any prior mitigation technology. First, air capture would take place in free-standing
dedicated plants, and so would offer complete flexibility in siting, timing, and scale.
Second, air capture would not be bound to any particular emissions stream, and so
could be conducted at large enough scale to make any enterprise, nation, or human
civilization as a whole, a net remover of carbon from atmosphere, rather than a
contributor to it.
1. The Benefits of Air Capture in a Dynamically Optimal Climate Response
Assuming cost trends that make air capture competitive with conventional mitiga-
tion by late this century, the authors examine its significance using a dynamically
optimizing integrated-assessment model. This analysis yields two important re-
sults. First, rather than atmospheric CO
2
concentration reaching some elevated
level at which it then stabilizes, optimal concentration time-paths reach some max-
imum value, then decline. This behavior arises from two characteristics of the
cost and benefit functions assumed in the model, which are plausible although
Climatic Change (2006) 74: 5–15
DOI: 10.1007/s10584-005-9032-z
c
Springer 2006