US President Barack Obama has called on world leaders to agree to cut carbon emissions at crucial talks in Paris later this year.
Speaking in Alaska, he said countries including his own were not doing enough to stop global warming.
World powers meet in Paris in December with the aim of agreeing to curb global temperature rises.
Mr Obama said now was the time "to protect the one planet we've got while we still can".
"On this issue - of all issues - there is such a thing as being too late,'' he told a meeting of foreign ministers from
countries with Arctic interests soon after arriving in Alaska. "That moment is almost upon us."
While the Paris meeting will seek a deal to limit the rise in global temperatures to 2°C, there have been warnings that the goal is unlikely to be achieved.
During his three-day tour of Alaska, Mr Obama will become the first sitting US president to visit the area above the Arctic Circle.
He will also hike on the Exit Glacier, that has suffered significant melts in recent years, and will appear in a television show with adventurer Bear Grylls.
President Obama has made the fight against climate change one of the cornerstones of his second term. Last month, he unveiled plans to cut US greenhouse gas emissions by almost a third over the next 15 years.
Some state governors said they would ignore the plan, while parts of the energy industry said they would fight it.