"Machine guns, fighter jets... are not our primary security concern. The single greatest threat to our very existence is climate change," Fiji Defence Minister Inia Seruiratu said.
He was addressing a summit in Singapore which has focused on China-US tensions and the Ukraine war.
Cyclones have repeatedly battered Fiji and other low-lying Pacific countries.
"It threatens our very hopes and dreams of prosperity. Human-induced, devastating climate change," Mr Seruiratu told the forum, called the Shangri-La Dialogue.