cbd-ts-66-en

Part I: Impacts of Climate-related Geoengineering on Biological Diversity
CHAPTER 5
POTENTIAL IMPACTS ON BIODIVERSITY OF CARBON DIOXIDE
REMOVAL GEOENGINEERING TECHNIQUES
5.1 GENERAL FEATURES OF CDR APPROACHES
5.1.1 Reducing the impacts of climate change
By removing carbon dioxide (CO2) from the atmosphere, CDR techniques are intended to reduce the concentration
of the main causal agent of anthropogenic climate change. In addition, they are expected to ameliorate ocean
acidification (Figure 2.1).
Any reductions in the negative impacts of climate change and ocean acidification on biodiversity (as summarized
in Chapter 3) that might be achieved by effective and feasible CDR techniques would therefore be expected
to have positive impacts on biodiversity, in a way that is far more certain than for SRM. However, as noted in
Chapter 2: (i) these beneficial effects are generally slow-acting; (ii) the climatic conditions resulting from a specific
atmospheric CO2 value may be different if CO2 is falling (as a result of a CDR measure) from the conditions
previously experienced at the same CO2 value when it was rising;259 and (iii) several CDR techniques are of only
modest or doubtful effectiveness,260, 261 with few (if any) considered realistically capable of fully offsetting current
anthropogenic carbon emissions.
In addition, any positive effects from reduced impacts of climate change and/or ocean acidification due to reduced
atmospheric CO2 concentrations may be offset (or, in a few cases, augmented) by additional, unintended impacts
on biodiversity of the particular CDR technique employed. Such additional impacts are summarised in Table 5.1,
and are reviewed on a technique-specific basis in sections 5.2 -5.7 below.
5.1.2 Carbon sequestration (removal and storage)
The term “carbon sequestration” was (provisionally) defined by the tenth meeting of the Conference of the Parties
to the CBD262 as “the process of increasing the carbon content of a reservoir/pool other than the atmosphere”.
However, in a geoengineering context this usage is ambiguous, since no temporal constraints are included. It is
therefore preferable to clearly recognise that carbon sequestration (through CDR geoengineering) necessarily
involves two steps:
54
i) removal of CO2 from the atmosphere; and
ii) long-term storage of the captured carbon, taking it out of circulation for a climatically-significant
period (e.g., at least 10 years, and preferably > 100 years).
These processes occur naturally, but the former does not necessarily lead to the latter. Thus most of the products
of either terrestrial or marine photosynthesis are recycled annually or on shorter timescales by plant, animal or
microbial respiration. Effective sequestration requires that both steps can be demonstrated. Nevertheless, the term
is sometimes used as the descriptor for only the latter, storage component,263 contrasting to the CBD’s definition
above that seems to focus only on the initial removal.
259 Chadwick et al. (2012).
260 Vaughan & Lenton (2011).
261 McLaren (2011).
262 Footnote to CBD decision X/33, paragraph 8(w).
263 In legal and/or financial usage, sequestration involves secure holding and access restrictions, e.g. of assets.