Ocean acidification continues to rise at a rate “unprecedented in Earth's history,” a direct result of past and current increases in carbon and greenhouse gas emissions, posing significant threats to the health and integrity of marine ecosystems and the diverse range of products and services they provide the world over, according to a report produced by the International Geosphere-Biosphere Programme, UNESCO's Intergovernmental Oceanographic Commission and the Scientific Committee on Oceanic Research (SCOR).
The latest scientific research on ocean acidification indicates the pH of the oceans is decreasing 10-times faster than at any time in the past 55 million years and may be decreasing faster “than at any time in the last 300 million years,” according to “Ocean Acidification: A Summary for Policymakers” presented at the Third Symposium on the Ocean in a High-CO2 World in Monterey, California in September.
The culprit: rising anthropogenic (human) emissions of CO2. The amount of carbon dioxide (CO2) in our atmosphere has risen 40 percent since the start of the Industrial Revolution. The oceans historically have absorbed about ¼ of all the CO2 released into the atmosphere by humans since that time. Today, they absorb some 10 million metric tons of CO2 on a daily basis, the report authors note in an executive summary. To date, those emissions have led ocean acidity to increase 26 percent.
Ocean acidification: Rising human carbon emissions the culprit
Increasing ocean acidification lowers the capacity of the oceans to absorb CO2 and hence hence lowers the capacity of the oceans to act as a climate change buffer. More broadly, it threatens the viability of marine ecosystems from the base up. That spells potential trouble for already troubled ocean plant and animal species, many of which are of vital importance to human societies the world over.
As the authors highlight, the gathering of 540 experts from 37 countries in Monterey, California for the Third Symposium on the Ocean in a High-CO2 World attests to the growing amount of interest, scientific research, and sense of urgency, regarding “ocean acidification, its impacts on ecosystems, socio-economic consequences and implications for policy.”
What do we need to do in response to what amounts as a “clear and present danger” to the health and integrity of marine ecosystems? The report authors state the solution plainly and succinctly:
“Reducing CO2 emissions is the only way to minimize long-term, large-scale risks.”
Considerations for Policy Makers
In the executive summary, they go on to highlight considerations they recommend policy makers take into account in their decision making:
- The primary cause of ocean acidification is the release of atmospheric CO2 from human activities. The only known realistic mitigation option on a global scale is to limit future atmospheric CO2 levels.
- Appropriate management of land use and land-use change can enhance uptake of atmospheric CO2 by vegetation and soils through activities such as restoration of wetlands, planting new forests and reforestation.
- Geoengineering proposals that do not reduce atmospheric CO2 – for example, methods that focus solely on temperature (such as aerosol backscatter or reduction of greenhouse gases other than CO2) – will not prevent ocean acidification. Adding alkaline minerals to the ocean would be effective and economically feasible only on a very small scale in coastal regions, and the unintended environmental consequences are largely unknown.
- The impacts of other stressors on ocean ecosystems such as higher temperatures and deoxygenation – also associated with increasing CO2 – will be reduced by limiting increases in CO2 levels.
- The shellfish aquaculture industry faces significant threats and may benefit from a risk assessment and analysis of mitigation and adaptation strategies. For example, seawater monitoring around shellfish hatcheries can identify when to limit the intake of seawater with a lower pH, hatcheries can be relocated, or managers can select larval stages or strains that are more resilient to ocean acidification for breeding.
- At local levels, the effects of ocean acidification on ecosystem resilience may be constrained by minimising other local stressors3,4,5 through the following:
- Developing sustainable fisheries management practices such as regulating catches to reduce overfishing and creating long-term bycatch reduction plans. If implemented and enforced, this type of management has been shown to sustain ecosystem resilience.
- Adopting sustainable management of habitats, increased coastal protection, reduced sediment loading and application of marine spatial planning.
- Establishing and maintaining Marine Protected Areas (MPAs) that help manage endangered and highly vulnerable ecosystems to enhance their resilience against multiple environmental stressors.
- Monitoring and regulating localised sources of acidification from runoff and pollutants such as fertilisers.
- Reducing sulphur dioxide and nitrous oxide emissions from coal-fired power plants and ship exhausts that have significant acidifying effects locally.
Main image credit: Christopher Krembs, TAMU