The Center for Biological Diversity, a major American climate advocacy group, has been trying to force the U.S. to more aggressively track and test for the phenomenon almost a decade. Last Thursday, the nonprofit sued the federal government to force the EPA to regulate ocean acidification under the Clean Water Act.

This might sound a little funny: Why is an outside group suing the Obama administration’s EPA to get it to take action on climate change?

In part, it’s because we only began to understand the phenomenon recently. Climate scientists only grasped ocean acidification as a crisis in the past two decades. Ocean acidification as a term was only coined in 2003; by contrast, the greenhouse effect has been generally understood among scientists since the 1980s. And the bulk of the science around the issue is even more recent: According to a West Coast scientific task force, 75 percent of all peer-reviewed science about ocean acidification was published in the last five years.

The Center for Biological Diversity began pushing the EPA to regulate ocean acidification in 2007. The Center’s attorneys believe that acidification should count as a pollutant under the Clean Water Act, a law that gives the agency broad administrative power to preserve the “chemical, physical, and biological integrity of the nation’s waters.” Specifically, the Center wants the agency to release a water-quality standard for ocean acidification—a move that will force all 50 states to adopted either the EPA’s standard or a more stringent one.

This is more than idle rule making. A water-quality standard would let the state agencies that monitor water quality decide which bodies of water are “impaired” by ocean acidification—a legal term that permits the state or the federal government to take more muscular action to restrict pollution.

But any attempt to get there will face two problems. The first is a doozy: No one’s quite sure how to measure ocean acidification yet. The Center and other researchers who study the problem say that the EPA’s current method doesn’t work—that is, you can’t just measure a bay’s pH level to know if it is harmed.

“pH is the current criteria relevant to ocean acidification, and it’s really difficult to get an impaired listing under pH,” says Emily Jeffers, an attorney at the Center for Biological Diversity. “The federal criteria says [waters] must remain within .2 of natural variation. But the pH of water has a natural variability, and we don’t have good data on that baseline.”

In the past century, the pH of ocean water has generally declined by .1, she said. The current EPA standard will not be triggered until global oceanic pH falls to .2 below baseline. But this represents more change than it sounds like, because the pH scale is logarithmic.