Twenty-two environmental organizations including Earthjustice, representing more than 5 million Americans, sent a letter to President Obama on Friday, urging him to lead the U.S. delegation at the Rio+20 Earth Summit in June and be a strong advocate for action on clean energy, environmental rights and healthy oceans.

More than 130 heads of state and government leaders are expected to attend. Like the first Earth Summit in Rio 20 years ago, this gathering will help set the international agenda on environment and sustainability for the next 20 years.

The Earth Summit presents a rare opportunity for the global community to ratchet up action on issues like healthy oceans in the face of new challenges like ocean acidification. Ocean acidification is thought by many to be the greatest threat to marine ecology in this century, and is squarely on the agenda at Rio+20. Coral reefs—the nurseries of the sea—along with the shelled creatures that form the base of the marine food web are among the species and ecosystems most vulnerable to acidification.

Redoubling efforts to build ocean ecosystem resilience to acidification by reducing local stressors such as pollution and overfishing, paired with ambitious CO2 reductions, is fundamental if we want diverse marine ecosystems to survive.

The United States should lead in advocating for strong language in the Earth Summit outcome document to catalyze action to build healthy, resilient ocean ecosystems by reducing pollution and overfishing, establishing protected areas to sustain ecosystems in the face of rising ocean acidification and other stressors, and enhancing coordinated global monitoring of ocean acidification. These steps are fundamental for livelihoods, food security and sustainable development in island and coastal states, as well as for coastal and fishing communities here at home.

I’ll be joining Earthjustice President Trip Van Noppen, Oceans Program Director Steve Roady and International program Managing Attorney Martin Wagner at the summit. Our team has been working to support the work of the Pacific Small Island Developing States and other champions for the oceans.

U.S. engagement at the highest level is critical to the Earth Summit’s success and to the future of green industry and jobs at home. With the heads of state of China, India, Russia, France and the United Kingdom along with many others already committed, the U.S. can’t afford not to be there.