Lawsuits may seem like a quixotic—or even counterproductive—strategy for tackling a problem as big as global warming, but lately they seem to be working. Last week, the EPA's appeals board blocked the permit for a new coal-fired plant in Utah, ruling that before the EPA handed out any more permits, the agency needed to determine whether the coal plants should employ "best available control technology" for carbon-dioxide emissions. The decision was, in effect, an implementation of the Supreme Court's ruling in Massachusetts v. EPA last year, which effectively held that the EPA has a responsibility, under the Clean Air Act, to regulate greenhouse-gas emissions.

But, given that climate change affects just about every facet of the global environment, why stop at using the Clean Air Act? That seems to be the legal philosophy of the Center for Biological Diversity (CBD), one of the three organizations that sued to have the polar bear listed under the Endangered Species Act, hoping to use the connection between the loss of Arctic sea ice and the bear's decline as a legal argument for limiting emissions. The polar-bear lawsuit was only partially successful—the bear was listed as threatened, but Interior Secretary Dirk Kempthorne announced that his agency would make no move to regulate greenhouse-gas emissions as a result. Now, though, the CBD has announced its plans to file another climate lawsuit, this time using the Clean Water Act. Their argument is that rising atmospheric carbon-dioxide levels are causing ocean acidification, a form of water pollution that the Clean Water Act requires the EPA to regulate.

It's an argument grounded firmly in science. The world's oceans have absorbed roughly half of all the carbon dioxide that humans have emitted since the beginning of the industrial revolution, a process that has caused the average pH of ocean water to drop by about 0.1 units. If carbon-dioxide emissions keep rising at their current rate, the result will be another 0.3 to 0.4 unit pH drop by the end of the century—which doesn't sound like a big deal until you remember that pH is expressed on a logarithmic scale. Ocean acidification makes it harder for marine organisms to build shells from calcium carbonate. It is already killing coral, and it could start to affect some of the hard-shelled plankton at the very bottom of the ocean food chain.

None of this exactly means that the Clean Water Act is the best reason for the EPA to start regulating carbon-dioxide emissions. Nor is it particularly clear, especially after last week, that the EPA really needs yet another legal reason to start regulating carbon dioxide. But you've got to hand it to the CBD for being persistent—and for making it tough to ignore the fact that there's hardly an inch of the globe, even underwater, that greenhouse-gas emissions aren't starting to impact.

--Rob Inglis, High Country News