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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.
Table 5.1: Classification of CDR techniques and summary of additional impacts relevant to biodiversity (other than climatic benefits via reduced radiative forcing). See text for discussion of available information on effectiveness and feasibility. Technique 1. Ocean fertilization 2. Enhanced weathering 3. Terrestrial ecosystem management 4. Biomass Location of side effects Capture Storage Direct external fertilization – Ocean – Up/downwelling modification – Ocean – Ocean alkalinity – Ocean ** – Ameliorates ocean acidification (OA) * ? Relocates OA effects from ocean surface to ocean interior Yes, but risk of local excess alkalinity Spreading of base minerals – Land *** – Yes Nature of potential additional impacts Some of these are very uncertain; all are highly scale-dependent Changes to phytoplankton productivity and diversity, food-webs and biogeochemical cycling; increased anoxia and acidification in deep sea Habitat destruction from mining and transport on land; high energy use; local impacts of excess alkalinity at sea Habitat destruction from mining and transport; high energy use; effects on soil structure and fertility; increased soil albedo Afforestation – Land – Yes Negative and positive impacts of land use change Reforestation – Land – Yes Generally positive impacts on forest ecosystems Soil carbon enhancement – Land – Yes Mostly positive impacts of soil carbon enhancements Biomass production Land N/A Yes Land-use/habitat change; potential for nutrient depletion Biofuels with CCS Subsurface N/A Charcoal storage Land OA amelioration achieved via CO2 removal (covered above) Above, plus estimated small risk of leakage from CCS storage Above , plus mostly benign but uncertain impacts on soil water retention and fertility; effects on N2O emissions; decreased albedo Ocean biomass storage Ocean Local leakage risk Above, plus damage to benthic environments 5. Direct air capture Either N/A Yes Minor land cover changes; water and energy use; pollution risks 6. Carbon storage Ocean CO2 storage Geological carbon reservoirs N/A Ocean Subsurface Severe local OA impacts Damage to deep sea ecosystems, via severe local ocean acidification Low leakage risk Estimated small risk of leakage * “Yes” in this column indicates that amelioration of ocean acidification is expected to be directly proportional to absolute or relative reduction achieved in atmospheric CO2. ** As indicated in right-hand column, ocean alkalinity will also have unintended, indirect impacts on land. *** Spreading of alkaline minerals will eventually have impacts (expected to be mostly positive) on shelf seas and ocean through river run-off.
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