Global warming is making both places more important to global shipping and trade. To imagine the kind of future a hotter, dryer climate may bring, and the geopolitical challenges it will create, look no farther than two parts of the world that Donald Trump wants America to control: Greenland and the Panama Canal.

Panama on Tuesday marked the 25th anniversary of the United States' handover of its interoceanic canal, a milestone overshadowed by President-elect Donald Trump's threat to demand control be returned to Washington.

The canal was turned over to Panama on Dec. 31, 1999. For Carter, the deal signified a new beginning of mutual respect and cooperation between the U.S. and Latin America, as he said in his speech in 1978. It also showed “the last remnant of alleged American colonialism is being removed” during a time when the world moved away from imperialism.

Carter viewed the Panama Canal transfer as a defining moment of his presidency, while Donald Trump recently reignited debate, calling it a "giveaway."

For dozens of US tourists watching a cargo ship pass through the Panama Canal, Donald Trump's threat to possibly wrest back control of the waterway is nonsensical.None of those interviewed backed US President-elect Trump in his repeated threats that he could seize control of the canal after he returns to the White House next month.