Tony de Brum saw the effects of rising seas from his home in the Marshall Islands and became a leading advocate for the landmark Paris Agreement and an internationally recognized voice in the fight against climate change.

De Brum, who was the Pacific nation’s climate ambassador and former foreign minister, died Tuesday in the capital Majuro surrounded by his family, according to Marshall Islands President Hilda Heine. He was 72.

After witnessing nuclear testing in the islands while growing up, de Brum fought against nuclear weapons and for his nation’s independence.

Heine described him as a national hero.

“The very existence of the Paris Agreement owes a lot to Tony de Brum,” Heine said. “He was a giant of history, a legend in every meaning of the word and a custodian of our shared future.”

When a reporter from The Associated Press visited de Brum at his Majuro home in 2015, he described how he’d grown up catching rabbitfish off Enebok Island, which was lush with coconut and breadfruit trees at the time.

But in recent years, the island has slipped beneath the water. When the AP visited the island with de Brum, all that remained at low tide was a pile of rocks that snagged flotsam including a sandal, some frayed rope and a sprouting coconut.

Though the Marshall Islands, population 70,000, remains one of the places most vulnerable to climate change because it protrudes just two meters above sea level, de Brum said at the time that he was determined to stay and fight.

“The thought of evacuation is repulsive to us,” he said. “We think that the more reasonable thing to do is to seek to end this madness, this climate madness, where people think that smaller, vulnerable countries are expendable and therefore they can continue to do business as usual.”

Heine said de Brum was 9 years old and fishing with his grandfather when he witnessed the horrors of “Bravo shot,” a U.S. thermonuclear test at Bikini Atoll.

Born in Tuvalu, de Brum became one of the first Marshallese to attend university and returned home to become a leading participant in negotiations that secured the nation’s compact of free association with the United States and membership to the United Nations.

Heine said de Brum remained committed to the cause of nuclear justice and global disarmament, as well as climate change.

During the negotiations for the Paris accord, de Brum helped form the “High Ambition Coalition” of 100 rich and poor nations and helped secure a global commitment to try to limit Earth’s warming to 2.7 degrees Fahrenheit compared to pre-Industrial times.

The U.S. signed up for the accord under President Barack Obama, but President Donald Trump announced in June that the nation would withdraw.

“He was incredibly important to all of us,” said Marshall Islands poet Kathy Jetnil-Kijiner, who is related to de Brum. “He is viewed for his work globally, but he was also a grandfather, an uncle, and a father, and was much more than his accomplishments.”

Jetnil-Kijiner wrote a poem dedicated to de Brum and Mattlan Zackhras, a government minister who died earlier this month and who was also dedicated to fighting climate change.

“They say there are no mountains, in the Marshalls, the land that is close, to an expiration date,” Jetnil-Kijiner wrote. “But I will tell you the mountains, were men, giants who walked across the sea, sounding the call for the world, to hear our story.”

Heine said de Brum is survived by his father, his wife Rosalie, three children, 10 grandchildren and five great-grandchildren.