Humans can’t live under water, so we tend to overlook the fact that most life on this planet exists not on land but in the oceans. “Oceans cover 71 percent of the earth’s surface area but contain 97 percent of its livable habitat,” says David Helvarg, author of Blue Frontier: Dispatches From America’s Ocean Wilderness. Oceans provide approximately 70 percent of the oxygen that humans breathe (like plants, oceans absorb carbon dioxide and release oxygen) and most of the water we drink (evaporation from oceans forms the clouds whose rain and snow fill rivers and aquifers). In evolutionary terms, adds Helvarg, humans come from the ocean–our earliest forebears crawled out of the sea eons before our immediate ancestors, the apes, began walking on two legs–which may explain why people are so drawn to it. Half the world’s population lives within fifty miles of a coastline; going to the beach is the number-one outdoor recreational activity for Americans.

Homo sapiens could not survive without oceans, but you wouldn’t know it from how we have been treating them. Climate change was the big environmental story of 2006, but the alarming state of the oceans was not far behind. Topping the list was a study published in Science that projected that edible sea life will completely disappear by 2048 if current trends of overfishing and pollution continue. “Our children will see a world without seafood if we don’t change things,” commented Boris Worm, lead author of the study, which found three years ago that 29 percent of fish and shellfish populations had collapsed. A separate report by the United Nations Environmental Program announced there are at least 200 oxygen-starved “dead zones” in the world’s seas, caused by excessive runoff of fertilizers, sewage and other land-based pollution. Further worrisome evidence came from the central Pacific Ocean, where Greenpeace researchers took samples from a swarm of floating plastic that stretched across an area the size of Texas. Suspended in a stagnant vortex of currents, the plastic came primarily from mainland consumers in Asia and North America. The Los Angeles River alone flushes enough trash each year to fill the Rose Bowl two stories high, according to a superb exposé in the Los Angeles Times.

Perhaps most ominous, human activity is altering the very chemical composition and temperature of the oceans. Scientists blame increasing emissions of carbon dioxide. The oceans absorb much of this CO2, which is fortunate in one sense; otherwise, the atmosphere would be heating up even faster than it already is. But the extra CO2 is making seawater more acidic, which in turn threatens a cascade of disturbing consequences, including the destruction of coral reefs and plankton, tiny animals that are the foundation of the marine food chain.

Nevertheless, Jane Lubchenco, a professor at Oregon State University who ranks among the most distinguished oceanographers in the world, sees reasons for hope. “We’re seeing the early stages of a mutiny for the bounty, if you will,” she says. “There is increasing awareness that the historic bounty of oceans is quickly disappearing but also that there’s still time to reverse the degradation.”

One sign of this incipient mutiny, says Lubchenco, is the similarity of recommendations made by two recent US blue-ribbon commissions on the oceans. The Pew Oceans Commission, on which Lubchenco served, was tilted toward the advocacy side of the debate; the US Commission on Ocean Policy, created by Congress, reflected establishment views. (They have since merged to form a joint commission.) But both diagnosed the state of the oceans as dire and recommended an overhaul of American policy–putting science first, respecting environmental limits and rationalizing government oversight. Current policy is schizophrenic, Lubchenco says: “Fisheries policy is handled by one agency, coastal development by another, water quality by yet another, habitat protection by still another, making it impossible to apply the holistic approach needed to foster resilient, healthy ecosystems.” Both commissions urged passage of a comprehensive law on oceans–“like the Clean Air Act,” says Helvarg–that would create a single entity to coordinate all federal policy on oceans and interact with state governments. The cost of the recommended reforms is relatively small: $3 billion to $4 billion a year–about what the United States spends every two weeks fighting the Iraq War.

So far, Congress and the Bush Administration have done little in response, earning a D+ on a Joint Ocean Commission Initiative report card last February. Since then, critics say, only incremental progress has been made, despite two high-profile initiatives: President Bush’s creation of the Northwestern Hawaiian Islands Marine National Monument, a Montana-sized reserve of mainly open water, and Congress’s reauthorization of the Magnuson-Stevens Act, which governs fisheries policy.

Nancy Knowlton, director of the Center for Marine Biodiversity and Conservation at the Scripps Institution of Oceanography, welcomed the Hawaii reserve but noted that it was a relatively easy step to take: The area is so remote that there is almost no commercial fishing there. “What we really need is to declare 20 percent of the world’s oceans no-take zones,” she says. “And we’re nowhere near that.” The other priority, Knowlton says, is to “get serious about global warming,” an imperative conspicuously omitted from both commissions’ policy recommendations.

Laura Cantral, a spokeswoman for the Joint Ocean Commission Initiative, praised the reform of Magnuson-Stevens for “enhancing the role of science” and “setting a clear deadline for ending overfishing.” But environmentalists complain that the act’s rhetoric is undermined by weak enforcement mechanisms. “We need to treat the ocean as what it is–an interrelated web of living organisms, rather than a seafood production factory,” says Michael Hirshfield, chief scientist at the group Oceana.

The new Congress is more environmentally friendly. It seems likely to pass the long-pending treaty on the Law of the Sea, which is favored by everyone from environmentalists to the fishing industry to the State Department but was blocked from a Senate vote by far-right opponents. Congress will also have a chance to emulate the best ocean policy in the nation, which, as usual in matters environmental, is found in California. Barbara Boxer, chair of the Senate Environment Committee, has promised to introduce a bill based on the California Ocean Protection Act.

But it will take much more than sensible legislation in the United States to restore the world’s ravaged ocean ecosystems. (US ocean policy is actually more progressive than that of most other nations, a refreshing change.) Dead zones cannot recover until agricultural systems worldwide abandon massive dependence on chemical fertilizers. The plastic vortex swirling in the central Pacific will keep growing until the throwaway culture that has taken hold in rich and poor countries alike is overturned. And no individual reforms will matter much if global warming isn’t reversed very soon. The oceans are too vast and mighty for humans to kill, but we have proven ourselves quite capable of poisoning, overfishing and heating them to a perilous degree. The question is not whether oceans can survive what humans are doing to them but whether humans can.