Rising sea levels, which may be due to declining polar ice levels, are threatening low-lying countries like Micronesia. Mori told the U.N. General Assembly that world leaders needed to take the growing threat seriously.
"Our very existence depends on it," he said. "Without international cooperation and assistance, we are helpless against the adverse impacts of climate change."
While expressing support for climate initiatives embraced during June's sustainability conference in Rio de Janeiro, he said the expiring Kyoto Protocol was cause for concern.
"How do I tell my people that their plight and their future lie in the hands of those most responsible for greenhouse gasses?" he asked.
Marshall Islands President Christopher Loeak issued a similar plea during his address to the United Nations earlier this week.
U.N. Secretary-General Ban Ki-moon described comprehensive action on climate change as "a major piece of unfinished business" during a climate conference held on the sidelines of the U.N. debate.
Qatar hosts a U.N. climate change beginning Nov. 26.