The focus of the public's concern over carbon emissions has been overwhelmingly fixated on the potential for future temperature increases. Accordingly, the legal wrangling has focused there as well, with lawsuits flying over states' ability to regulate automotive CO 2 output and whether the EPA needs to treat it as a pollutant due to the climate impact. But a paper that will appear in Geophysical Research Letters (a PDF of a draft is available) suggests this legal wrangling may be besides the point: the impact of atmospheric CO 2 on the oceans should exceed EPA standards within decades, and cuts in emissions need to be made immediately if we're to avoid harming key species.

The impact of atmospheric carbon on the ocean is no secret within the scientific community, but it has yet to pervade the public consciousness. It's based on simple chemistry: atmospheric CO 2 exists in equilibrium with its dissolved form in water, and that dissolved form is a weak acid. Increase the CO 2 in the air, and bodies of water will gradually get more acidic unless they have some way of eliminating the carbon.

Separate from any arguments over its effect on climate, pretty much everyone agrees that atmospheric CO 2 levels are increasing, from about 280 parts-per-million in preindustrial times to about 380ppm in the current day. That increase has been accelerating, so that we're expected to hit 500ppm within four decades. Continuing at the current pace would have us clear 750ppm before the century is over.

The consequences of that 500ppm level is where the new paper comes in. The paper started out as what appears to be an academic spat; an article published by a single author last year in the same journal suggested that the impact of this change on the acidity of the ocean will be relatively mild, and specifically phrased (for no obvious reasons) it in terms of being within water quality standards set by the EPA: even by the end of the century, it claimed, the pH of the ocean will be within the EPA's recommended levels.

The new publication is a response to that earlier work and was prepared by a large collection of authors that work at many prestigious institutes around the globe. The response hammers the original publication, suggesting that it is flawed at nearly every level. "Based on inappropriate assumptions and erroneous thermodynamic calculations," the new report states, "[the 2006 paper] mistakenly reports that atmospheric CO2 concentrations of 760 ppm will lower the pH of the surface ocean by 0.28 relative to the natural 'mid 18th century' conditions." For those who do not normally follow the scientific literature, having three separate accusations of error in the second sentence of a paper is very rare.

According to the authors of the new work, the original paper went astray largely because of its assumption that atmospheric carbon will equilibrate instantly across the entire body of the ocean; instead, this process is expected to take 5-10,000 years. That error, along with a number of more technical problems, led the original paper to grossly underestimate the pH changes that will be caused by the increase in atmospheric carbon. The net result is that even reaching 500ppm of CO 2 in the atmosphere will cause the ocean to exceed the acceptable pH change in EPA's Water Quality Criteria.

The authors of the paper go on to detail how the ocean pH criteria was set in 1976 and doesn't even reflect current information on its likely impact. The current data suggests that, before the century is out, we may reach the point where coral reefs begin receding due to a combination of erosion and having the coral simply dissolve into the increasingly acidic seas. Many forms of plankton that sit at the base of the oceanic food chain may also have difficulty building their mineral skeletons under the expected pH conditions. Given the expected trajectory of carbon emissions and the time involved in the ocean's equilibration, the clear implication is that emissions will have to be cut drastically and nearly immediately to keep things within the recommended range.

Will the EPA do so? Their water quality standards were designed to aid the development of strategies for meeting specific targets but, as the agency notes, "the strategy does not impose legally binding requirements on EPA, states, tribes or the regulated community." Still, the paper is likely to increase the pressure on the agency, as it obviates the two arguments the EPA has used to defend its current inaction: questioning whether carbon dioxide-induced warming represented pollution in any way, and questioning whether warming posed a risk of material damage.

If the paper's arguments reach the broader public, they also may shift the debate over carbon emissions in general. Many people have a hard time grasping century-scale temperature change and melting ice caps; water pollution and crashing fisheries are things that many people and governments have more immediate experience with.