Climate change impacts on the biophysics and economics of world fisheries

Global marine fisheries are underperforming economically because of overfishing, pollution and habitat degradation. Added to these threats is the looming challenge of climate change. Observations, experiments and simulation models show that climate change would result in changes in primary productivity, shifts in distribution and changes in the potential yield of exploited marine species, resulting in impacts on the economics of fisheries worldwide. Despite the gaps in understanding climate change effects on fisheries, there is sufficient scientific information that highlights the need to implement climate change mitigation and adaptation policies to minimize impacts on fisheries.

Ocean acidification and climate change: synergies and challenges of addressing both under the UNFCCC

Ocean acidification and climate change are linked by their common driver: CO2. Climate change is the consequence of a range of GHG emissions, but ocean acidification on a global scale is caused solely by increased concentrations of atmospheric CO2. Reducing CO2 emissions is therefore the most effective way to mitigate ocean acidification. Acting to prevent further ocean acidification by reducing CO2 emissions will also provide simultaneous benefits by alleviating future climate change. Although it is possible that reducing CO2 emissions to a level low enough to address ocean acidification will simultaneously address climate change, the reverse is unfortunately not necessarily true. Despite the ocean’s integral role in the climate system and the potentially wide-ranging impacts on marine life and humans, the problem of ocean acidification is largely absent from most policy discussions pertaining to CO2 emissions. The linkages between ocean acidification, climate change and the United Nations Framework Convention on Climate Change (UNFCCC) are identified and possible scenarios for developing common solutions to reduce and adapt to ocean acidification and climate change are offered. Areas where the UNFCCC is currently lacking capacity to effectively tackle rising ocean acidity are also highlighted.

L’acidification des océans et le changement climatique sont liés par leur cause commune : le CO2. Alors que le changement climatique est la conséquence d’une série d’émissions de gaz à effet de serre, l’acidification des océans à l’échelle planétaire est causée seulement par l’accroissement des concentrations en CO2 dans l’atmosphère. La manière la plus efficace pour atténuer l’acidification des océans est de réduire les émissions de CO2. Agir pour empêcher davantage d’acidification dans les océans en diminuant les émissions de CO2 entraînera également des avantages simultanés dans l’atténuation de changements climatiques futurs. Alors qu’il est possible de réduire les émissions de CO2 à un niveau suffisamment bas pour atténuer l’acidification des océans, tout en s’attaquant simultanément au changement climatique, l’inverse n’est malheureusement pas forcement le cas. Malgré le rôle intégral des océans dans le système climatique et les effets potentiels étendus sur la vie marine et les humains, le problème de l’acidification des océans est largement absent de la plupart des discussions politiques liées aux émissions de CO2. Les liens entre acidification des océans, le changement climatique et la Convention cadre des Nations Unies sur le changement climatique (CCNUCC) sont identifiés et des scénarios possibles pour développer des solutions communes pour réduire et s’adapter à l’acidification des océans et le changement climatique sont proposés. Les domaines où la CCNUCC manque actuellement de capacités pour lutter effectivement contre l’acidité croissante des océans sont aussi mis en valeur.

Mitigating local causes of ocean acidification with existing laws

As the level of atmospheric carbon dioxide (CO2) continues to rise, so too does the amount of CO2 in the ocean, which increases the ocean’s acidity. This affects marine ecosystems on a global scale in ways we are only beginning to understand: for example, impairing the ability of organisms to form shells or skeletons, altering food webs, and negatively affecting economies dependent on services ranging from coral reef tourism to shellfish harvests to salmon fisheries. Although increasing anthropogenic inputs drive acidification at global scales, local acidification disproportionately affects coastal ecosystems and the communities that rely on them. We describe policy options by which local and state governments—as opposed to federal and international bodies—can reduce these local and regional “hot spots” of ocean acidification.

CO2 mitigation via capture and chemical conversion in seawater

A lab-scale seawater/mineral carbonate gas scrubber was found to remove up to 97% of CO₂ in a simulated flue gas stream at ambient temperature and pressure, with a large fraction of this carbon ultimately converted to dissolved calcium bicarbonate. After full equilibration with air, up to 85% of the captured carbon was retained in solution, that is, it did not degas or precipitate. Thus, above-ground CO₂ hydration and mineral carbonate scrubbing may provide a relatively simple point-source CO₂ capture and storage scheme at coastal locations. Such low-tech CO₂ mitigation could be especially relevant for retrofitting to existing power plants and for deployment in the developing world, the primary source of future CO₂ emissions. Addition of the resulting alkaline solution to the ocean may benefit marine ecosystems that are currently threatened by acidification, while also allowing the utilization of the vast potential of the sea to safely sequester anthropogenic carbon. This approach in essence hastens Nature’s own very effective but slow CO₂ mitigation process; carbonate mineral weathering is a major consumer of excess atmospheric CO₂ and ocean acidity on geologic times scales.

Geoengineering potential of artificially enhanced silicate weathering of olivine

Geoengineering is a proposed action to manipulate Earth’s climate in order to counteract global warming from anthropogenic greenhouse gas emissions. We investigate the potential of a specific geoengineering technique, carbon sequestration by artificially enhanced silicate weathering via the dissolution of olivine. This approach would not only operate against rising temperatures but would also oppose ocean acidification, because it influences the global climate via the carbon cycle. If important details of the marine chemistry are taken into consideration, a new mass ratio of CO2 sequestration per olivine dissolution of about 1 is achieved, 20% smaller than previously assumed. We calculate that this approach has the potential to sequestrate up to 1 Pg of C per year directly, if olivine is distributed as fine powder over land areas of the humid tropics, but this rate is limited by the saturation concentration of silicic acid. In our calculations for the Amazon and Congo river catchments, a maximum annual dissolution of 1.8 and 0.4 Pg of olivine seems possible, corresponding to the sequestration of 0.5 and 0.1 Pg of C per year, but these upper limit sequestration rates come at the environmental cost of pH values in the rivers rising to 8.2. Open water dissolution of fine-grained olivine and an enhancement of the biological pump by the rising riverine input of silicic acid might increase our estimate of the carbon sequestration, but additional research is needed here. We finally calculate with a carbon cycle model the consequences of sequestration rates of 1–5 Pg of C per year for the 21st century by this technique.

Coral reef remote sensing: helping managers protect reefs in a changing climate

Climate change and ocean acidification are already having severe impacts on coral reef ecosystems. Warming oceans have caused corals to bleach, or expel their symbiotic algae (zooxanthellae) with alarming frequency and severity and have contributed to a rise in coral infectious diseases. Ocean acidification is reducing the availability of carbonate ions needed by corals and many other marine organisms to build structural components like skeletons and shells and may already be slowing the coral growth. These two impacts are already killing corals and slowing reef growth, reducing biodiversity and the structure needed to provide crucial ecosystem services. NOAA’s Coral Reef Watch (CRW) uses a combination of satellite data, in situ observations, and models to provide coral reef managers, scientists, and others with information needed to monitor threats to coral reefs. The advance notice provided by remote sensing and models allows resource managers to protect corals, coral reefs, and the services they provide, although managers often encounter barriers to implementation of adaptation strategies. This talk will focus on application of NOAA’s satellite and model-based tools that monitor the risk of mass coral bleaching on a global scale, ocean acidification in the Caribbean, and coral disease outbreaks in selected regions, as well as CRW work to train managers in their use, and barriers to taking action to adapt to climate change. As both anthropogenic CO2 and temperatures will continue to rise, local actions to protect reefs are becoming even more important.

Adaptation to impacts of greenhouse gases on the ocean

Greenhouse gases are producing changes in ocean temperature and circulation, and these changes are already adversely affecting marine biota. Furthermore, carbon dioxide is absorbed by the oceans from the atmosphere, and this too is already adversely affecting some marine ecosystems. And, of course, sea-level rise affects both what is above and below the waterline. Clearly, the most effective approach to limit the negative impacts of climate change and acidification on the marine environment is to greatly diminish the rate of greenhouse gas emissions. However, there are other measures that can be taken to limit some of the negative effects of these stresses in the marine environment. Marine ecosystems are subject to multiple stresses, including overfishing, pollution, and loss of coastal wetlands that often serve as nurseries for the open ocean. The adaptive capacity of marine environments can be improved by limiting these other stresses. If current carbon dioxide emission trends continue, for some cases (e.g., coral reefs), it is possible that no amount of reduction in other stresses can offset the increase in stresses posed by warming and acidification. For other cases (e.g., blue-water top-predator fisheries), better fisheries management might yield improved population health despite continued warming and acidification. In addition to reducing stresses so as to improve the adaptive capacity of marine ecosystems, there is also the issue of adaptation in human communities that depend on this changing marine environment. For example, communities that depend on services provided by coral reefs may need to locate alternative foundations for their economies. The fishery industry will need to adapt to changes in fish abundance, timing and location. Most of the things we would like to do to increase the adaptive capacity of marine ecosystems (e.g., reduce fishing pressure, reduce coastal pollution, preserve coastal wetlands) are things that would make sense to do even in the absence of threats from climate change and ocean acidification. Therefore, these measures represent “no regrets” policy options for the marine environment. Nevertheless, even with adaptive policies in place, continued greenhouse gas emissions increasingly risk damaging marine ecosystems and the human communities that depend on them.

Influence of mitigation policy on ocean acidification

This study quantifies the relative impact on future ocean acidification of different aspects of global climate change mitigation policies, such as the year that global emissions peak, how fast they reduce after their peak, and the long term minimum emissions that are possible. Relative to a scenario where emissions peak in 2016 and then decrease by 1% per year, further emissions reductions to 2, 3 and 4% per year lead to the same impact minimum pH (by 2100) if emissions peak 10, 15 and 17 years later respectively. Over the same time scale, non-mitigation scenarios lead to a decrease of global mean surface pH of 7.67 to 7.81. Strong and urgent mitigation, emissions peaking in 2016 and reducing by 5% per year, are shown to limit this minimum to 8.02. Minimum pH over longer timescales, the next 500 years, is largely determined by the minimum emission level that is attainable, owing to its relation with cumulative emissions.

Can ocean iron fertilization mitigate ocean acidification?

Ocean iron fertilization has been proposed as a method to mitigate anthropogenic climate change, and there is continued commercial interest in using iron fertilization to generate carbon credits. It has been further speculated that ocean iron fertilization could help mitigate ocean acidification. Here, using a global ocean carbon cycle model, we performed idealized ocean iron fertilization simulations to place an upper bound on the effect of iron fertilization on atmospheric CO₂ and ocean acidification. Under the IPCC A2 CO₂ emission scenario, at year 2100 the model simulates an atmospheric CO₂ concentration of 965 ppm with the mean surface ocean pH 0.44 units less than its pre-industrial value of 8.18. A globally sustained ocean iron fertilization could not diminish CO₂ concentrations below 833 ppm or reduce the mean surface ocean pH change to less than 0.38 units. This maximum of 0.06 unit mitigation in surface pH change by the end of this century is achieved at the cost of storing more anthropogenic CO₂ in the ocean interior, furthering acidifying the deep-ocean. If the amount of net carbon storage in the deep ocean by iron fertilization produces an equivalent amount of emission credits, ocean iron fertilization further acidifies the deep ocean without conferring any chemical benefit to the surface ocean.

Benefits, risks, and costs of stratospheric geoengineering

Injecting sulfate aerosol precursors into the stratosphere has been suggested as a means of geoengineering to cool the planet and reduce global warming. The decision to implement such a scheme would require a comparison of its benefits, dangers, and costs to those of other responses to global warming, including doing nothing. Here we evaluate those factors for stratospheric geoengineering with sulfate aerosols. Using existing U.S. military fighter and tanker planes, the annual costs of injecting aerosol precursors into the lower stratosphere would be several billion dollars. Using artillery or balloons to loft the gas would be much more expensive. We do not have enough information to evaluate more exotic techniques, such as pumping the gas up through a hose attached to a tower or balloon system. Anthropogenic stratospheric aerosol injection would cool the planet, stop the melting of sea ice and land-based glaciers, slow sea level rise, and increase the terrestrial carbon sink, but produce regional drought, ozone depletion, less sunlight for solar power, and make skies less blue. Furthermore it would hamper Earth-based optical astronomy, do nothing to stop ocean acidification, and present many ethical and moral issues. Further work is needed to quantify many of these factors to allow informed decision-making.