A small uninhabited island that has slipped beneath the water line shows only a small pile of rocks at low tide on Majuro Atoll in the Marshall Islands on November 5, 2015. To small island nations, the United States pulling out of the Paris climate-change pact makes their future seem fragile. (Rob Griffith/AP)

To small island nations where the land juts just above the rising seas, the U.S. pulling out of the Paris climate change pact makes the future seem as fragile and built on hope as a sand castle.

Top scientists say it was already likely that Earth’s temperatures and the world’s seas will keep rising to a point where some island states may not survive the next 100 years. That likelihood increases, they say, if the United States doesn’t follow through on promised cuts in heat-trapping carbon dioxide emissions. President Trump this month said he plans to withdraw the United States from the climate deal, prompting leaders of vulnerable islands to talk about their future with a mixture of defiance, hope and resignation.

“If we really push into action, we can save some [small islands], but we may not be able save all of them,” said Hans-Otto Poertner, a German scientist who chairs the climate impacts study group for the United Nations Intergovernmental Panel on Climate Change. “The chances are even less with the U.S. pulling out of the climate agreement in Paris.”

Hilda Heine, president of the Marshall Islands (a chain of islands in the Pacific), called Trump’s announcement “deeply disappointing.”

“I cannot give up on my people and my country and my culture,” she said. “It’s very important for us to be optimistic.”

A boat lies wrecked and stuck on a sea wall after it crashed into the back of Foreign Minister Tony de Brum’s house in the Marshall Islands in November 2015. Scientists say that even with U.S. support for the agreement, it was likely that Earth’s temperatures and the world’s seas would rise to a point where some island states won’t survive 100 years. (Rob Griffith/AP)

Heine and other island leaders are putting their hope in strong pollution curbs by China, other nations, individual American states and cities, as well as improved technology. While visiting Europe, she said, “it’s all the more important that Europe takes the lead on climate change.”

The State Department said it considers engagement with other counties on climate change important and it will continue, including with small island states. Secretary of State Rex Tillerson said after Trump pulled out of the agreement that the United States has cut its carbon dioxide emissions “dramatically” even before the Paris pact was reached.

When the Paris pact was being negotiated in 2015, small island nations successfully campaigned for a stricter but secondary target for limiting global heat-trapping emissions.

In 2009, world leaders adopted a goal to prevent 2 degrees Celsius (or 3.6 degrees Fahrenheit) of warming since 1850 to 1900, saying 2 degrees is a dangerous level of warming. The islands’ tougher goal would try to limit warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) since that time period.

The world has already warmed about 1 degree Celsius since then, so the islands are really trying to prevent an additional half-degree of warming Celsius (0.9 degrees Fahrenheit).

When Trump announced he would pull the United States out of the Paris treaty, scientists said that made the 2-degree goal close to unachievable and the 1.5 degree goal even more out of reach. Promised American pollution cuts were about one-fifth of the pledged global reductions hoped for in the accord.

“We are pushing the 1.5 [as a goal], but realistically I think we have passed the point that it can be achieved,” said Kenrick Leslie of the Caribbean Community Climate Change Centre.

Ahmed Sareer, the Maldives ambassador to the United Nations and chairman of the Alliance of Small Island States, said the 1.5 goal is harder to achieve without the United States but not yet impossible.

“The island spirit is to never give up,” Sareer said. “We are always a resilient people.”