Move over global warming. Ocean acidification is getting its day in court.Nearly three years after the US Supreme Court found that carbon dioxide was a pollutant that fell under the purview of the Clean Air Act, the US Environmental Protection Agency has agreed to explore approaches for tightening its regulations dealing with ocean acidification under the Clean Water Act.Ocean acidification results from the ocean's uptake of carbon dioxide from the atmosphere. Many scientists have become increasingly concerned about the effect industrial emissions of CO2 are having on the chemistry of the world's oceans and about the fallout for many species of marine animals.The oceans take up as much as half the CO2 emissions humans pump into the atmosphere each year.The agreement, reached Thursday in the US District Court in Seattle, stems from a 2009 lawsuit filed by the Center for Biological Diversity, a conservation group based in San Francisco.The center argued that the acidity in Washington State's coastal waters had increased sufficiently to violate EPA standards, but that the state and the EPA failed to list the waters as "impaired." That designation triggers a process for reducing pollution levels to prevent the condition from getting worse.While the settlement falls short of the Center for Biological Diversity's goal, the agreement "creates a public process for the EPA to prepare guidance for all the states with coastlines on how to address ocean acidification," says Miyoko Sakashita, the center's point person on ocean issues.That includes helping states assess and monitor the chemistry of their coastal waters, working with them to determine acceptable daily maximum levels of acidification, and providing support as they try to develop regulations controlling the pollutant involved: carbon dioxide.The notion of an expanded EPA role isn't new. The pH of coastal waters has been regulated since 1976. Last year, the EPA began digging into the issue, seeking a broad range of information on the topic as it relates to human CO2 emissions.But given the resistance in Congress and in corporate boardrooms to the prospect that the EPA would regulate CO2 emissions under the Clean Air Act, the settlement's small step toward cracking down on CO2 emissions via the Clean Water Act represents another "oh, no" moment.Yet as a practical matter, any meaningful regulation may be at least a decade away, even if opposition to the effort could be swept aside.A lack of baseline information on the pH of coastal waters is one stumbling block."I've been monitoring these changes for the past 30 years," says Richard Feeley, a marine scientist at the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory in Seattle. "There's no doubt these changes are occurring and that they are man-made changes."Moreover, he adds, only three sites currently have data on ocean pH that span a sufficient amount of time to be useful to regulators. One is in Monterey Bay off California. The other two are open-ocean sites.At a minimum, regulators would need at least a decade's worth of data at each of dozens of sites along a coastline to be able to confidently detect trends.And only a handful of labs around the country are set up to make the precise pH measurements any regulations would require. "The changes we expect to see are about 0.002 pH units a year," Dr. Feeley says.Moreover, a dearth of information on the biological effects of increased acidity still exists, adds Scott Doney, a researcher at the Woods Hole Oceanographic Institution in Woods Hole, Mass. Several important lab studies have been conducted, along with field studies, that have raised red flags. "But there's not a lot of information yet," he says, especially on an ecosystem-wide basis.Still, Feeley says, the settlement represents an important new step as the EPA gathers information "on the kinds of criteria they should be thinking about."