Oceans’ rising acid levels have emerged as one of the biggest threats to coral reefs, acting as the “osteoporosis of the sea” and threatening everything from food security to tourism to livelihoods, the head of a U.S. scientific agency said. The speed by which the oceans’ acid levels has risen caught scientists off-guard, with the problem now considered to be climate change’s “equally evil twin,” National Oceanic and Atmospheric Administration chief Jane Lubchenco told The Associated Press.

Oceans absorb excess carbon dioxide in the atmosphere, increasing sea acidity. Scientists are worried about how that increase will affect sea life, particularly reefs, as higher acid levels make it tough for coral skeletons to form.