disappear. it can super charge storms, melt our glaciers and bleach our coral reefs. bleached corals are still alive, but they are extremely stressed. highly vulnerable, and if the heat continues, they may die. this is part of why scientists worry. the first location we dove to was south of key biscayne. we saw exactly what we feared, this is the moving front of severe bleaching up through the keys and now up into miami-dade. reporter: it was just a remarkable moment to stand next to these century-old giants, right? i mean, how else do you describe it? but it was very eye-opening to see this you a ray of a mixture of completely dead coral, bleached coral, and healthy coral. so i saw hope, but i also saw a tough situation and i can see what heat stress really does to these animals. they are sensitive, and i witnessed it. it was humbling. is there still hope?