Global warming is altering—and threatening to erase—much more of the Marshall Islands than the shorelines of this independent Micronesian nation that once served as a Pacific Ocean nuclear weapons test site for the U.S. It is changing the vocabulary and heightening the risk of extinguishing the language and culture of daily life. Locals already have integrated the phrases "climate change" and "seawall" into the nation's two predominant dialects of the Marshallese language, which is unique to this archipelagic country. Its islands and atolls didn't need such walls in the past, but sea-level rise and urbanization have recently forced citizens to live closer to shore—which has led to the erection of seawalls.

Residents of low-lying islands in the Pacific and Indian oceans are among those who will feel the effects of climate change to the greatest degree in the coming decades. Some are already seeing the consequences of rising sea levels in the form of higher tides. "When the tide comes up, it's literally up to someone's house or up to the road," says Kristina Stege, a New York City resident who grew up in the Republic of the Marshall Islands and frequently returns to visit her family. Marshall Islanders have also suffered from erosion and fresh water scarcity as a result of climate change she says.

Some island governments have even begun thinking about whether they may have to relocate their entire populations, should sea levels rise high enough to render their idyllic homelands uninhabitable. Such a move would have a profound impact on the unique languages and cultures including Pacific islanders—and in the Marshalls, locals have been talking about new ideas and phenomena as they've seen the preliminary effects of a changing climate on their coasts.

More significantly, if Pacific islanders are forced to leave their homes permanently, their languages may change fundamentally, picking up new grammar and pronunciation, and, ultimately, may even face extinction.

"I like to think that if the worst happens and if everyone had to leave the country because of climate change," says anthropologist Peter Rudiak-Gould, "maybe this emphasis on keeping good traditional things would help some aspects of the culture to be retained and perhaps the language as well." But he is not sure: "It's really hard to predict." Rudiak-Gould is a doctoral student at the University of Oxford who studies climate change and culture in the Marshall Islands, a nation of 469 square kilometers scattered among five islands and 29 coral atolls.

In February unusually high tides—"higher than anyone has ever remembered," Stege says—sparked conversations about climate change among Marshall Islanders. Until then global warming had been mostly a topic for government officials. As awareness has spread, however, it has added new words and concepts to the islands' unique language, furthering the increasing Westernization and modernization on the Marshallese language. Elders worry about how modernization pushes out words for traditional skills, such as long-distance canoe navigation. Meanwhile, linguists are concerned for the longevity of local languages.

Linguists recognize that languages naturally evolve over time and nobody advocates preserving a language as it is used in a freeze-frame. But the world is culturally and intellectually poorer for every language that dies out. Different tongues "contain interesting features that show what the human mind can do with language," says Byron Bender, a University of Hawaii an Manoa linguist who created the Marshallese–English Online Dictionary.

There are only 65,000 to 75,000 speakers of Marshallese in the world—about the population of the wine-producing city of Napa, Calif. The speakers include the 60,000 citizens of the Republic of the Marshall Islands and 5,000 to 15,000 Marshallese immigrants in the U.S. The language is a part of the Austronesian language family and is related to many Pacific languages, among them Samoan and Fijian.

Climate change brought so many new concepts to Marshallese culture that people simply folded English words into Marshallese to describe them at first, Rudiak-Gould says. "Marshallese people have been put into an unfortunate position where the changes in the country are so large that their traditional knowledge isn't sufficient to understand them," he says.

The large-scale importation of foreign words tends to happen when a culture encounters a sizeable, sudden influx of new items, says Juliette Blevins, co-director of the Endangered Language Alliance (ELA) in New York City. Every Pacific island that is a former U.S. protectorate, such as the Federated States of Micronesia (which, along with the Marshalls, maintains a Compact of Free Association with the U.S.), has thousands of what linguists call loanwords taken from English. The loanwords describe pencils (pinjel in Marshallese), radios (retio), cars (kaar)—things that Americans brought with them when they arrived after World War II as trustees of what was then the United Nations–created Trust Territory of the Pacific Islands.

But recently, Marshall Islanders have come up with Marshallese terms to replace English ones. "There's this realization that we need our own words," Stege says. People now use okoktak in mejatoto interchangeably with climate change, says Marie Maddison, a resident of the Marshalls' capital city, Majuro. Okoktak in mejatoto literally translates to "changes in our skies". People also say kooj, which means "blanket," for the greenhouse effect.

Linguists do not consider taking in loanwords a major language change—rather, alterations in grammar or pronunciation are seen as more fundamental alterations. That's not happening now but it may if everyone on the Marshalls eventually evacuates because of sea-level rise, Marshallese dictionary author Bender says. Evacuees will probably go to the U.S., Rudiak-Gould notes, because the nation's compact with the U.S. allows Marshallese people to live and work in the U.S. easily. There does not yet exist, however, a legal agreement about where the Marshallese would go if everybody had to evacuate the islands at once.

If they were to relocate to the U.S., Marshallese speakers would find themselves suddenly in a sea of English. New neighbors who speak a different language are the driving force in major language change, Bender says.

An en masse move to the U.S. could even drive the Marshallese language to extinction. "It could disappear," Rudiak-Gould says.

Marshallese isn't currently considered endangered. That's because language endangerment is not about numbers but about whether there are plenty of young speakers with parents to teach the language to them. Marshallese remains a vibrant, living language that's the native tongue of every Marshall Islander.

But immigrant languages do not have a history of surviving well in the U.S., ELA researchers say. "In America, it's been said that immigrant languages don't survive more than two generations," Blevins notes. In other words, immigrants' children speak their home language, but their grandchildren do not. For example, Yiddish was lost in two generations in the U.S. outside of Orthodox Jewish communities, Blevins' co-director, Daniel Kaufman says.

Language extinction isn't inevitable. Marshallese has characteristics that make it both vulnerable and resistant to extinction. People are likely to lose their language if they're a small minority, if they have little political power and if popular media, such as TV and radio, aren't aired in their language, Rudiak-Gould says. "Environmental refugees like post-evacuation Marshall Islanders would check all of these boxes."

But Marshallese immigrants live in tightly knit communities, such as one in Springfield, Ark., which may include as many as 10,000 Marshallese-Americans. People living in the Marshalls take pride in their culture, and the government there maintains a language preservation commission. "We have reason to be proud of our forefathers, who boldly ventured across the unknown waters of the vast Pacific Ocean," reads the preamble to the Constitution of the Republic of the Marshall Islands. "All we have and are today as a people, we have received as a sacred heritage, which we pledge ourselves to maintain."

"Our constitutional preamble recognizes the resiliency of our people," Maddison says. She founded a nonprofit organization, Women United Together Marshall Islands, that will plant native food trees along the coastline there to combat erosion and food insecurity. The group also holds workshops to teach people to make traditional foods such as breadfruit flour and preserved pandanus.

"I don't know, I don't know," Stege says when asked whether she thinks the Marshallese language could survive in the U.S. "With my children, I try to speak Marshallese, and when I go back home, people always appreciate that." People haven't given up on the Marshall Islands, she adds. They're still investing in their communities. They're not thinking about leaving their land.

"Mostly people are living their lives," she says. But it's a life that's affected more and more by climate change. Stege says her neighbors in the Marshall Islands worry most about the cost of food and electricity and about having enough water. "A lot of these things are related to climate change, right?"