The world's scientific community is calling for urgent actions to halt rising levels of acidity in the world's oceans.
The surface ocean currently absorbs about one-fourth of the CO2 emitted to the atmosphere from human activities, namely from fossil-fuel combustion, deforestation, and cement production. (The photo is a reprint of 'The Great Wave off Kanagawa' by the Japanese artist Katsushika Hokusai.)
We scientists who met in Monaco* to review what is known about ocean acidification declare that we are deeply concerned by recent, rapid changes in ocean chemistry and their potential, within decades, to severely affect marine organisms, food webs, biodiversity, and fisheries.
To avoid severe and widespread damages, all of which are ultimately driven by increasing concentrations of atmospheric carbon dioxide (CO2), we call for policy makers to act quickly to incorporate these concerns into plans to stabilize atmospheric CO2 at a safe level to avoid not only dangerous climate change but also dangerous ocean acidification.
The surface ocean currently absorbs about one-fourth of the CO2 emitted to the atmosphere from human activities, namely from fossil-fuel combustion, deforestation, and cement production. As this CO2 dissolves in seawater, it forms carbonic acid, increasing ocean acidity.
Since industrialization began in the 18th century, surface-ocean acidity has increased by 30%. This ongoing ocean acidification is decreasing the ability of many marine organisms to build their shells and skeletal structure. Increasing acidity and related changes in seawater chemistry also affect reproduction, behaviour, and general physiological functions of some marine organisms, such as oysters, sea urchins, and squid.
Observations collected over the last 25 years show consistent trends of increasing acidity in surface waters that follow increasing atmospheric CO2. These trends match precisely what is expected based on basic marine chemistry and continuous measurements of atmospheric CO2. A range of field studies suggest that impacts of acidification on some major marine calcifiers may already be detectable.
Also, naturally high-CO2 marine environments exhibit major shifts in marine ecosystems following trends expected from laboratory experiments. Ocean acidification has altered some coastal waters to the extent that recently during spring they have become corrosive to the shells of some bottom dwelling organisms. Within decades these shell-dissolving conditions are projected to be reached and to persist throughout most of the year in the polar oceans.
Currently the average concentration of atmospheric CO2 is 385 parts per million (ppm), which is 38% more than the preindustrial level of 280 ppm. Half of that increase has occurred in the last 30 years. Current CO2 emissions are greater than projected for the worst-case scenario formulated a decade ago. And along with increasing emissions, the increase in atmospheric CO2 is accelerating.
By mid-century, the average atmospheric CO2 concentration could easily reach double the preindustrial concentration. At that 560- ppm level, it is expected that coral calcification rates would decline by about one-third. Yet even before that happens, formation of many coral reefs is expected to slow to the point that reef erosion will dominate. Reefs would no longer be sustainable. By the time that atmospheric CO2 reaches 450 ppm, it is projected that large areas of the polar oceans will have become corrosive to shells of key marine calcifiers.
Ocean acidification could affect marine food webs and lead to substantial changes in commercial fish stocks, threatening protein supply and food security for millions of people as well as the multi-billion dollar fishing industry. Coral reefs provide fish habitat, generate billions of dollars annually in tourism, protect shorelines from erosion and flooding, and provide the foundation for tremendous biodiversity, equivalent to that found in tropical rain forests. Yet by mid-century, ocean acidification may render most regions chemically inhospitable to coral reefs.
These and other acidification-related changes could affect a wealth of marine goods and services, such as our ability to use the ocean to manage waste, to provide chemicals to make new medicines, and to benefit from its natural capacity to regulate climate. For instance, ocean acidification will reduce the ocean’s capacity to absorb anthropogenic CO2, which will exacerbate climate change.
The current increase in ocean acidity is a hundred times faster than any previous natural change that has occurred over the last many millions of years. By the end of this century, if atmospheric CO2 is not stabilized, the level of ocean acidity could increase to three times the preindustrial level. Recovery from this large, rapid, human-induced perturbation will require thousands of years for the Earth system to re-establish ocean chemical conditions that even partially resemble those found today; hundreds of thousands to millions of years will be required for coral reefs to return, based on the past record of natural coral-reef extinction events.
So-called geo-engineering strategies that would not aim to restrict future atmospheric CO2 concentrations would not reduce ocean acidification. Mitigation strategies that aim to transfer CO2 to the ocean, for example by direct deep sea disposal of CO2 or by fertilising the ocean to stimulate biological productivity, would enhance ocean acidification in some areas while reducing it in others. Climate-change negotiations focused on stabilizing greenhouse gases must consider not only the total radiation balance; they must also consider atmospheric CO2 as a pollutant, an acid gas whose release to the atmosphere must be curtailed in order to limit ocean acidification. Hence, limits (stabilization targets) for atmospheric CO2 defined based on ocean acidification may differ from those based on surface temperature increases and climate change.
Despite a seemingly bleak outlook, there remains hope. We have a choice, and there is still time to act if serious and sustained actions are initiated without further delay. First and foremost, policy makers need to realize that ocean acidification is not a peripheral issue. It is the other CO2 problem that must be grappled with alongside climate change. Reining in this double threat, caused by our dependence on fossil fuels, is the challenge of the century.
Solving this problem will require a monumental worldwide effort. All countries must contribute, and developed countries must lead by example and by engineering new technologies to help solve the problem. Promoting these technologies will be rewarded economically, and prevention of severe environmental degradation will be far less costly for all nations than would be trying to live with the consequences of the present approach where CO2 emissions and atmospheric CO2 concentrations continue to increase, year after year.
Fortunately, partial remedies already on the table, if implemented together, could solve most of the problem. We must start to act now because it will take years to change the energy infrastructure and to overcome the atmosphere’s accumulation of excess CO2, which takes time to invade the ocean.
Therefore, we urge policy makers to launch four types of initiatives:
E-mail: J.Orr@iaea.orgThis document is based on the report Research Priorities for Ocean Acidification, available online at: http://ioc3.unesco.org/oanet/HighCO2World.html