Submerged countries, abandoned cities and floods of refugees await the world barring urgent action on climate change, US President Barack Obama has warned.
Obama painted the doomsday scenario as he opened a historic visit to Alaska.
In a bid to further his environmental legacy, he called on other nations to take swift action as negotiations for a global climate treaty near a close.
In a speech to an Arctic climate summit in Anchorage, Obama sought to set the tone for a three-day tour of Alaska that will put the state's liquefying glaciers and sinking villages on graphic display.
"On this issue - of all issues -there is such a thing as being too late," Obama said.
"And that moment is almost upon us."
During his tour, Obama plans to hike a glacier, meet with fishermen and tape a reality TV show with survivalist Bear Grylls - all part of a highly orchestrated White House campaign to illustrate how climate change has damaged Alaska's stunning landscape.
Evoking ominous consequences, Obama said that climate change left unchecked will soon trigger global conflict and "condemn our children to a planet beyond their capacity to repair".
In the Arctic, which is warming faster than any other corner of the globe, Obama said melting permafrost and disintegrating sea ice risk floods, fires and unimaginable economic damage.
"It's already changing the way Alaskans live," Obama said.
Obama has two audiences in mind as he traverses the state this week: Alaskans, who are hungry for more energy development to boost the state's sagging oil revenues, and the broader public, whose focus Obama hopes to concentrate on the need for drastic action to combat global warming, including a climate treaty that he hopes will help solidify his environmental legacy.
But whether Obama can successfully navigate those competing interests - energy and the environment - remained the prevailing question of his trip.
His tour continues on Tuesday (local time) with a boat tour Kenai Fjords National Park and a hike to Exit Glacier, a sprawling expanse of ice that is retreating amid warming temperatures.
On Wednesday (local time) in southwest Alaska, Obama will meet with fishermen locked in conflict with miners over plans to build a massive gold and copper mine in Bristol Bay, home to the world's largest salmon fishery.
And he will close his trip by becoming the first sitting president to travel north of the Arctic Circle in Kotzebue - population 3153.