Quotes of the Day

Imagine flying over a section of clear-cut rainforest, somewhere in the Amazon. Even after the bulldozers were gone and the fires had smoked out, you would know that something had happened on this land. You would see the scar that the forest once was, and know that it was wrong.

Now imagine this destruction submerged deep under the ocean — perhaps off the coast of South America, near the remote Galapagos Islands. Flying over the open water, all you would see is clear, blue sea, untouched, not a boat on the horizon. You wouldn't know that beneath the surface, the ocean was hurting — or that humans were the cause.

But human-related injury to the oceans is rife. We have fished out an estimated 90% of the major commercial fish species that swim the high seas, including the giant and endangered blue fin tuna. The trawlers carrying out that destruction are raking the ocean floor, turning parts of the once vibrant continental shelf into so much mud. Climate change is warming the oceans, disrupting the fundamental structure of the marine food pyramid and destroying coral reefs. Meanwhile, increased concentrations of CO2 in the atmosphere are making the seas acidic, which threatens to kill off species in large numbers. "The ocean is becoming a desert," says Jeremy Jackson, the director of the Center for Marine Biodiversity and Conservation at the Scripps Institution of Oceanography.

Pollution that has washed off the land — from sewage that contains chemical toxins to nitrate fertilizer from farmland — has infected the oceans, destroying once vibrant coastal waters. But it's a problem we barely notice, since for many of us the oceans are distant and out of sight. "We are using the oceans as a sewer," says Jean-Michel Cousteau, son of the great French marine explorer and filmmaker, and a documentary maker himself. "But because we're visual creatures and we can't see what's going on, we don't relate."

That ignorance is apparent even in the work of conservationists. Despite the fact that oceans make up nearly 70% of the planet and generate most of the oxygen we breathe, just a fraction of the total philanthropic money donated to green causes finds its way to safeguarding the seas. Today about 12% of the world's land area is under some form of protection, be it a national park, monument or reserve. By contrast 0.8% of the world's oceans are contained within what are called marine protected areas (MPAs), and just a tiny sliver of these areas fall under no-fishing zones. The shelters that do exist are mainly in near-coastal waters, within the 200-mile exclusive economic zones that nations can claim off their shores, but more than half the ocean lies beyond this territory on the high seas, which belong to no single government — a fact that explains in part why comparatively little ocean conservation has been achieved. April 22 may be the 40th anniversary of Earth Day, but it's the oceans that really need our attention now.

The good news is that, like their counterparts on land, marine protected areas can make a significant difference in ocean health. They give the seas a break from human influence and allow sea life a chance to recover. The breadth of life beneath the waves — from the blue whale, the biggest animal that ever lived, to the tiny microscopic creatures of the deep sea — is unsurpassed. "When it come to the diversity of life on Earth, the oceans are where the action is," says Sylvia Earle, a famed oceanographer and former chief scientist of the National Oceanic and Atmospheric Administration. "But we look at the ocean like a Neanderthal would: is it good to eat? Or is it going to eat me?"

Despite recent setbacks (notably the failure in March of member states of the Convention on International Trade in Endangered Species to pass a ban on the global trade of the endangered Atlantic bluefin tuna), there has at least been a steady rise in creation of new MPAs around the world. Toward the end of his time in office, former President George W. Bush — nobody's idea of a great environmentalist — created a 132,000-sq.-mi (341,400-sq-km) protected area off the northwestern Hawaiian Islands. At the beginning of April, the British government announced it would establish the world's largest MPA, around the Chagos Archipelago in the middle of the Indian Ocean, putting it off limits to industrial fishing. "We know that protected areas are very important," says Callum Roberts, a marine conservation biologist at the University of York. "They breathe life back into the oceans."

Going forward, the challenge will be expanding protected areas beyond the puddle they currently occupy and into the high seas, where virtually no protection currently exists. That is the mission Earle — known as "Her Deepness" to her many admirers in oceanography — has set herself at age 74. In early April, with help from the tech-world nonprofit TED, Earle launched Mission Blue, a new nonprofit dedicated to protecting "hope spots," as Earle calls them.

Among Earle's first targets are the Patagonia shelf off southeastern Argentina and the Sargasso Sea, the 1.4 million or so square miles (3.6 million sq km) of underwater rainforest east of Bermuda. What they have in common is their unique value to the marine world, their size — and the fact that they're under threat. "This is the way to protect the ocean, the heart of the planet," says Earle.

Already, Mission Blue has generated nearly $17 million in donations for ocean protection, and there's already movement afoot to declare the Sargasso Sea a protected area, which would be by far the biggest MPA in the world. Some of the money is going towards a campaign that would end subsidies for fishing fleets, which might be the quickest method to reducing the plague of industrial overfishing. But the effectiveness of even established MPAs must be strengthened in the meantime, in order to prevent mishaps like the Chinese coal freighter that ran aground this month on the Great Barrier Reef off Australia, leaking fuel onto perhaps the most iconic marine spot on the planet.

Accidents like that may be impossible to ignore, but the damage that humans are causing miles beneath the surface must be addressed as well. "This is our life support system," says Earle. "We take care of the ocean, and we take care of ourselves."

• Bryan Walsh
• For years, it was thought that Earth's oceans were too vast to succumb to human-caused harm, but damage is growing evident, in the form of overfishing, pollution and global warming