Over the past 200 years, the oceans have absorbed approximately a quarter of the CO₂ produced from human activities. This CO₂ would otherwise have accumulated in the atmosphere leading to greater climate change. However, the absorption of this CO₂ has affected ocean chemistry and has caused the oceans (which are on average slightly alkaline) to become more acidic.

The average pH of oceanic surface waters has been lowered by 0.1 units since the pre-industrial period. This represents a 30% increase in hydrogen ion activity. Hydrogen ions attack carbonate ions which are the building blocks needed by many marine organisms, such as corals and shellfish, to produce their skeletons, shells and other hard structures. This loss of carbonate ions produce lower saturation levels for the carbonate minerals, aragonite and calcite, which are used in many shells and skeletons. Carbonate ion concentrations are now lower than at any other time during the last 800,000 years.

Ocean acidification is irreversible during our lifetimes and those of many generations to come, according to the IAP statement. Minimizing the risk of these large-scale and long-term changes to the oceans requires curbing the the increase in atmospheric CO₂ concentrations by reducing emissions from human activities by at least 50% by 2050.

Recent scenario studies have estimated that stabilization of atmospheric CO₂ concentrations at 550 ppm will produce enough acidification to be disastrous for sensitive oceanic ecosystems in many parts of the world. Even at 450 ppm, more than 10% of the world’s oceans will be impacted including large parts of the Southern, North Pacific, and Arctic oceans.

Mitigation approaches such as adding chemicals to counter the effects of acidification are likely to be expensive, only partly effective and only at a very local scale, and may pose additional unanticipated risks to the marine environment. There has been very little research on the feasibility and impacts of these approaches, the IAP noted. Substantial research is needed before these techniques could be applied.

There has been much talk among the science community over the past few years about ocean acidification and its potentially catastrophic consequences, but it has failed to receive the political attention it demands. Its absence from discussions to-date is of immense concern, and we call for its immediate inclusion as a vital part of the climate change agenda.

—IAP Co-Chairs, Chen Zhu, Minister of Health, P.R. of China; and Howard Alper, Chair and President, Science, Technology and Innovation Council, Canada

The statement calls for world leaders to explicitly recognize the direct threats posed by increasing atmospheric CO₂ emissions to the oceans and its profound impact on the environment and society. It emphasizes that ocean acidification is irreversible and, on current emission trajectories, suggests that all coral reefs and polar ecosystems will be severely affected by 2050 or even earlier.

The implications of ocean acidification cannot be overstated. Unless we cut our global CO2 emissions by at least 50% by 2050 and thereafter, we could be looking at fundamental and immutable changes in the makeup of our marine biodiversity. The effects will be seen worldwide, threatening food security, reducing coastal protection and damaging the local economies that may be least able to tolerate it.

—Zhu and Alper

The statement was issued during the UNFCCC conference in Bonn this week that will ultimately shape the Copenhagen negotiations, where agreement must be reached on carbon emission reduction targets needed to avoid dangerous climate change.