David Obura, a marine biologist and co-chairman of the coral specialist group for the International Union for Conservation of Nature, praised certain

 David Obura, a marine biologist and co-chairman of the coral specialist group for the International Union for Conservation of Nature, praised certain restoration efforts but noted that without climate action, they are all but useless.

“With the main drivers of impact continuing to rise, they may just ‘buy time’ for just a few years,” Dr. Obura wrote in an email. “It is of course critical to attempt this, but this must not distract focus on addressing what and who is causing the problem.”

As the natural warming cycle of El Niño is compounded by climate change, he expects “several years of massive coral bleaching” around the world.

Beyond Florida, bleaching is already underway in reefs off the Bahamas, Belize, Colombia, Costa Rica, Cuba, El Salvador, Mexico and Panama.

Ms. Thomasson returned to Looe Key on Friday, getting her first look at the reef where she’d hoped to one day plant the now-dead young coral from the nursery. Thickets of wild elkhorn and mounds of brain coral were bleached or already dead. She clung to the knowledge that her group’s sites in the Upper Keys were faring better, so far.

Ms. Thomasson is determined to keep working on coral restoration, but she needs an ocean hospitable to corals for them to return to.

“It’s up to everyone else to demand climate action right now,” Ms. Thomasson said. “Not in a year, not tomorrow, but right now. Actually yesterday.”