POLICY BRIEF N°17/12 NOVEMBER 2012 | BIODIVERSITY Ocean acidification - what can we do? Raphaël Billé (IDDRI-Sciences Po), Ryan Kelly (University of Washington and Center for Ocean Solutions), Arne Biastoch (GEOMAR), Ellycia Harrould-Kolieb (Melbourne University), Dorothée Herr (IUCN), Fortunat Joos (University of Bern), Kristy Kroeker (University of California Davis), Dan Laffoley (IUCN), Andreas Oschlies (GEOMAR), Jean-Pierre Gattuso (CNRS-INSU and UPMC) This policy brief is based on a more comprehensive research published by Environmental Management in 2013 and available at http://link.springer.com/article/10.1007%2 Fs00267-013-0132-7. It is the second version of policy brief 17/12 published in November 2012 and replaces the previous one. CAUSES AND CONSEQUENCES OF OCEAN ACIDIFICATION The oceans have absorbed about one third of anthropogenic carbon dioxide (CO2) emissions during the past five decades. This massive input of CO2 generates sweeping changes in the chemistry of seawater, especially on the carbonate system. These changes are collectively referred to as “ocean acidification” because increased CO2 lowers seawater pH (i.e., increases its acidity). The basic chemistry of ocean acidification being well understood, future projections are quite straightforward for the surface open ocean for a given atmospheric CO2 trajectory. Those based on the International Panel on Climate Change (IPCC) scenarios give reduc- tions in average global surface pH of between 0.14 and 0.35 units over the 21st century, which means surface pH may reach 7.81 in the year 2100 (Orr, 2011)—compared to 8.18 prior to the industrial era and 8.10 at present. Furthermore, impacts related to ocean acidification Institut du développement durable will continue to aggravate for centuries even if emissions are stopped (Joos et al., 2011). et des relations internationales 27, rue Saint-Guillaume www.iddri.org 75337 Paris cedex 07 France 1. On the total scale. Ocean acidification - what can we do? Although the ocean’s uptake of atmospheric CO2 OPTIONS TO TAKE ACTION AGAINST is by far the major driver of ocean acidification OCEAN ACIDIFICATION globally, two other known or potential causes of ocean acidification have been identified: Preventing ocean acidification m Coastal acidification due to additional pol- lutants: Nitrogen and phosphate runoff from Given the three potential causes of acidification, agricultural, industrial, urban and domestic this may be done through: sources causes acidification of coastal waters. The relative importance of each of these mecha- Limiting CO2 concentration in the atmos- nisms—as well as the importance of each rela- phere, either by reducing emissions or by remov- tive to that of global CO2—is a matter of active ing CO2 once emitted. CO2 and other GHGs have research, but it seems clear that non-CO2 inputs been the primary target of the United Nations can contribute significantly to the overall acidi- Framework Convention on Climate Change (UN- fication threat in some coastal regions (Feely et FCCC) since its adoption in 1992, and of all sub- al., 2012). sequent climate talks. International climate ne- m Release of methane hydrates into the ocean: gotiations, however, have failed to reach a legally Methane hydrates currently stored in the sedi- binding, long-term agreement that would include ments below the ocean represent a significant all major and emerging economies to reduce CO2 fraction of the amount of carbon globally stored. and other GHGs emissions so as to meet the target Owing to high pressure and cold temperature of limiting global average temperature rise to less conditions, methane today remains in stable than 1.5 to 2oC above pre-industrial levels. Regard- hydrate form below 300 m. Deep oceanic war- less, this politically accepted limit chosen “to pre- ming could cause a transition from the hydrate vent dangerous anthropogenic interference with into the gas phase. Microbial aerobic oxidation the climate system”2 may not effectively address would then convert methane remaining in the ocean acidification for two reasons. First, it is still water column, with oxygen, into CO2, thus unclear what level of atmospheric CO2 may con- contributing to ocean acidification. Due to the stitute a “safe” level with respect to ocean acidifi- thermal inertia of the ocean and the delayed cation. Second, climate talks deal with cumulative intrusion of heat into the sediments, the process radiative effects and do not prioritize reductions of methane release would be irreversible and on any one gas (CO2 instead of others). would continue for a long time, even after glo- Removing CO2 from the atmosphere once emit- bal warming has eventually stopped. However ted, on the other hand, could also prevent ocean there is no consensus, as of today, as to whether acidification. Of the methods that aim to enhance the dissolution of methane hydrates represents uptake and storage by terrestrial and oceanic bio- a real and significant threat to the oceans in the logical systems, or to use engineered (physical, course of the 21st century. chemical, biochemical) systems, “none has yet been demonstrated to be effective at an affordable Consequences of ocean acidification on societies cost, with acceptable side effects” (The Royal So- will depend on interactions among and between ciety, 2009). Their effectiveness to reduce ocean species and ecosystems (all reacting at different acidification is technique specific and they hold lit- rates and magnitudes), on the interaction of ocean tle promise in terms of the maximum reduction in acidification with other ocean stressors; and on atmospheric CO2 they might realistically achieve responses of each human group affected. Never- (Williamson and Turley, 2012). However, calls to theless, it is clear that the speed and magnitude evaluate the potential, costs and benefits of geo- of acidification is threatening many marine spe- engineering solutions to ocean acidification grow cies and ecosystems. Calcifying organisms such as louder every day. coral reefs, shellfish and zooplankton are among the first potential victims. Therefore ocean acidi- Reducing local factors of ocean acidification fication will impact various economic sectors (e.g. is another lever for mitigating acidification in the fisheries, aquaculture, and tourism) and coastal coastal ocean3 (Kelly et al., 2011). The potential for communities, and may also have heavy indirect effects on much broader segments of the world economy and population. It is thus an appropri- 2. UNFCCC, Article 2. ate time to review the available management and 3. For the open ocean, which is likely to experience the policy options despite the uncertainties surround- effects of coastal stressors less directly, such policy levers are probably both less important (likely to have less ing the details of acidification impacts. effect) and less feasible (given the governance issues of the high seas). 2 POLICY BRIEF 17/2012 IDDRI Ocean acidification - what can we do? nutrient controls and other local- and national- importance for ocean acidification. This includes scale pollution control measures depends on the but is not limited to well-connected and represent- relative importance of non-CO2 inputs in driving ative networks of marine protected areas. ocean acidification, but they could be of critical The evidence for human-mediated increases in importance in areas where the chemical effects resilience is sparse, and building resilience is not of terrestrial inputs rival CO2-driven acidification. a solution to ocean acidification per se. Ultimate- Where local and national economies rely heavily ly, increasing resilience will only be effective as upon carbonate-dependent ecosystem services, a harm-mitigation technique if it is accompanied for example shellfish farming and coral tourism, by a strong limitation of CO2 concentration in the reducing local acidifying factors could produce re- atmosphere. sults both faster and in a more politically feasible manner than would a global CO2 solution alone. Adapting human activities in Reducing the risks of a potential release of anticipation of or reaction methane hydrates by limiting the greenhouse to ocean acidification effect, hence ocean warming, may be done either by reducing emissions of GHGs or by managing Adaptation to ocean acidification covers a wide solar radiation. To the extent that we really have range of potential actions taken by individuals an acidification problem exacerbated in the long- or human groups, and such measures will inevi- term by the rise of global temperatures, some non- tably be necessary given the inertia of past CO2 CO2 GHG emissions reductions appear technologi- emissions’ effect on present and future ocean cally feasible and politically viable (e.g., for PFCs, acidification. SF6 or HFCs). However, any such measures would Practical examples are still scarce, but revenue- not be sufficient by themselves to significantly generating activities like fisheries or aquaculture limit warming, largely driven by CO2 during this will have opportunities to adapt to an acidified century. On the other hand, methods for manag- ocean as the knowledge base improves and ing solar radiation, and therefore thermal impacts, impacts become more noticeable. The potential of have gained some attention. However, Williamson adaptation is likely to be high for certain specific and Turley (2012) conclude that their effects on activities and issues within a narrow range of pH acidification are uncertain in both their magni-