In the waning hours of last year's talks, the United States, China and a few other large emitters drafted a non-binding three-page "accord" urging "deep cuts in global emissions" to keep the average rise in global temperature below 2 degrees C (3.6 F). As the atmosphere has warmed, the oceans have absorbed more heat, expanding their mass and driving a rise in sea levels and a bleaching of coral reefs around the globe.
Worldwide, about 1billion people rely on reefs for their livelihoods and nutrition. Seychelles' spectacular reefs, a draw for tourists, are also spawning grounds for fish.
A growing number of scientists say that warming should be held to 1.5 degrees C to prevent widespread catastrophic consequences. Small island states and developing nations such as Bangladesh, convinced they will be inundated if it gets any warmer than that, are demanding that Cancun negotiators commission a study on the effects of a 1.5-degree target.
"Our mantra is, 'One-point-five to stay alive,'" Jumeau said.
But the move has been blocked by Saudi Arabia, the world's largest oil producer.
"Our beaches are eroding and our reefs are collapsing," Jumeau said. "I'm not talking about what climate change will do in the future. I'm talking about what it is doing right now."
Seychelles' government is placing protective granite boulders along the coast. But "stronger waves are battering the beaches," Jumeau said. "Much of the capital sits below sea level. We are in danger of losing our airport, our fishing port, our beaches, our hotels."
With its thriving tourism, Seychelles doesn't qualify for development aid given to poorer countries. "But we can't afford the interest on international bank loans," Jumeau said, adding that much of the money the World Bank and industrial nations plan to offer is in the form of loans.
"How is that fair?" he asked. "It is as if someone drives a car into your backyard, smashes the fence, crushes your garden and kills your plastic flamingo. Then he says, 'I'll give you a loan for messing up your yard, but you must pay me back.'"
As he sits in a cavernous negotiating hall, flanked by delegates from Serbia and Sierra Leone, Jumeau lets the diplomatic jargon from the monitors overhead wash over him: mitigation, adaptation, transparency, shared but differentiated responsibility.
"We know we won't get the agreement we want," he mused. "We're trying to get the best we can."