The first time I cried underwater was in 2008, the island of Curaçao, way down in the southern Caribbean. It's beautiful there. I was studying these corals for my PhD, and after days and days of diving on the same reef, I had gotten to know them as individuals. I had made friends with coral colonies -- totally a normal thing to do. Then, Hurricane Omar smashed them apart and ripped off their skin, leaving little bits of wounded tissue that would have a hard time healing, and big patches of dead skeleton that would get overgrown by algae. When I saw this damage for the first time, stretching all the way down the reef, I sunk onto the sand in my scuba gear and I cried. If a coral could die that fast, how could a reef ever survive? And why was I making it my job to try to fight for them? I never heard another scientist tell that kind of story until last year. A scientist in Guam wrote, "I cried right into my mask," seeing the damage on the reefs. Then a scientist in Australia wrote, "I showed my students the results of our coral surveys, and we wept." Crying about corals is having a moment, guys. (Laughter) And that's because reefs in the Pacific are losing corals faster than we've ever seen before. Because of climate change, the water is so hot for so long in the summers, that these animals can't function normally. They're spitting out the colored algae that lives in their skin, and the clear bleached tissue that's left usually starves to death and then rots away. Then the skeletons are overgrown by algae. This is happening over an unbelievable scale. The Northern Great Barrier Reef lost two-thirds of its corals last year over a distance of hundreds of miles, then bleached again this year, and the bleaching stretched further south. Reefs in the Pacific are in a nosedive right now, and no one knows how bad it's going to get, except ... over in the Caribbean where I work, we've already been through the nosedive. Reefs there have suffered through centuries of intense human abuse. We kind of already know how the story goes. And we might be able to help predict what happens next. Let's consult a graph. Since the invention of scuba, scientists have measured the amount of coral on the seafloor, and how it's changed through time. And after centuries of ratcheting human pressure, Caribbean reefs met one of three fates. Some reefs lost their corals very quickly. Some reefs lost their corals more slowly, but kind of ended up in the same place. OK, so far this is not going very well. But some reefs in the Caribbean -- the ones best protected and the ones a little further from humans -- they managed to hold onto their corals. Give us a challenge. And, we almost never saw a reef hit zero. The second time I cried underwater was on the north shore of Curaçao, 2011. It was the calmest day of the year, but it's always pretty sketchy diving there. My boyfriend and I swam against the waves. I watched my compass so we could find our way back out, and he watched for sharks, and after 20 minutes of swimming that felt like an hour, we finally dropped down to the reef, and I was so shocked, and I was so happy that my eyes filled with tears. There were corals 1,000 years old lined up one after another. They had survived the entire history of European colonialism in the Caribbean, and for centuries before that. I never knew what a coral could do when it was given a chance to thrive. The truth is that even as we lose so many corals, even as we go through this massive coral die-off, some reefs will survive. Some will be ragged on the edge, some will be beautiful. And by protecting shorelines and giving us food to eat and supporting tourism, they will still be worth billions and billions of dollars a year. The best time to protect a reef was 50 years ago, but the second-best time is right now. Even as we go through bleaching events, more frequent and in more places, some corals will be able to recover. We had a bleaching event in 2010 in the Caribbean that took off big patches of skin on boulder corals like these. This coral lost half of its skin. But if you look at the side of this coral a few years later, this coral is actually healthy again. It's doing what a healthy coral does. It's making copies of its polyps, it's fighting back the algae and it's reclaiming its territory. If a few polyps survive, a coral can regrow; it just needs time and protection and a reasonable temperature. Some corals can regrow in 10 years -- others take a lot longer. But the more stresses we take off them locally -- things like overfishing, sewage pollution, fertilizer pollution, dredging, coastal construction -- the better they can hang on as we stabilize the climate, and the faster they can regrow. And as we go through the long, tough and necessary process of stabilizing the climate of planet Earth, some new corals will still be born. This is what I study in my research. We try to understand how corals make babies, and how those babies find their way to the reef, and we invent new methods to help them survive those early, fragile life stages. One of my favorite coral babies of all time showed up right after Hurricane Omar. It's the same species I was studying before the storm, but you almost never see babies of this species -- it's really rare. This is actually an endangered species. In this photo, this little baby coral, this little circle of polyps, is a few years old. Like its cousins that bleach, it's fighting back the algae. And like its cousins on the north shore, it's aiming to live for 1,000 years. What's happening in the world and in the ocean has changed our time horizon. We can be incredibly pessimistic on the short term, and mourn what we lost and what we really took for granted. But we can still be optimistic on the long term, and we can still be ambitious about what we fight for and what we expect from our governments, from our planet. Corals have been living on planet Earth for hundreds of millions of years. They survived the extinction of the dinosaurs. They're badasses. (Laughter) An individual coral can go through tremendous trauma and fully recover if it's given a chance and it's given protection. Corals have always been playing the long game, and now so are we. Thanks very much. (Applause)