The ocean is our greatest ally in the fight against climate change: by absorbing 93 percent of the heat trapped by greenhouse gasses and about one quarter of the carbon dioxide that we produce when we burn fossil fuels, the ocean has slowed the rate of climate change, saving us from what would otherwise have been catastrophic warming. But this defense is affecting the ocean’s health, leading to rising water temperatures and sea levels, increased acidification, and decreased oxygen levels. As a result, our oceans—and the people who rely on them—are suffering. We are seeing dramatic events such as changes in fish migration, declines in fishery productivity, and corrosive waters along our shores. We must act now to ensure the health of our ocean and the safety and wellbeing of our coastal residents.