Coral reefs are vital to both human societies and the ocean's ecosystem—they protect shorelines from storm surges and erosion and serve as nurseries for marine life. They're also frighteningly imperiled by warming waters, which produce conditions that turn them a ghostly white and expose them to a blanket of algae. That's what Kim Cobb saw one day in 2016 when she swam up to the reef in the central Pacific's Line Island chain that she'd been studying for 18 years. A heat wave had killed or bleached 95 per cent of the corals.
"It was carnage," the Georgia Tech climate scientist recalls. Disturbances like pollution and fishing are relatively limited in the vicinity of the research site, so Cobb felt rising ocean temperatures were the likely culprit. The impact has already been devastating, she says, adding, "I can't even imagine what it would look like at 2 degrees Celsius."

If warming can be limited, however, there might be hope for the corals that remain. Scientists like Hollie Putnam are engineering so-called super corals with the ability to withstand higher ocean temperatures and acidity levels. Putnam, a marine biologist at the University of Rhode Island, places coral species under climate change stressors and breeds those that survive best, creating hyper-resilient organisms. "They're really exciting and really hopeful," Putnam says, noting that super corals could help maintain the biodiversity and genetic diversity of already struggling reefs, like the ones in the Line Island Chain.

But super corals are more likely to survive if warming doesn't get much worse. "If we push the climate system to 2 degrees Celsius, we're talking about 1 per cent of reefs surviving," Cobb says. "That makes it less likely that coral-resilience engineering efforts will succeed." She says it's essential to limit warming to 1.5 degrees, a scenario in which up to 30 per cent of reefs could survive on their own. If that happens, one of the world's wildest reefs could be strengthened. If it doesn't, even the savviest engineering intervention won't be enough.

Select the most appropriate synonym of the word surges stated in para1 of the given passage.

1. A
   Diminishes
2. B
   Contracts
3. C
   Gushes
4. D
   Decreases