Panama Canal, Panama

When the Panama Canal opened in 1914, it revolutionized shipping by providing an alternative to the southern route around Cape Horn. About 4 percent of world trade now passes through the canal. Raising and lowering ships between the Atlantic and Pacific oceans, which differ by 85 feet in elevation, requires vast amounts of increasingly scarce fresh water. Shortages have forced several closures in recent years.

Monteverde Cloud Forest, Costa Rica

For most of the year, the humidity level in this tropical forest reaches 100 percent. With majestic trees festooned with orchids, bromeliads, ferns, vines, and mosses, it’s home to a multitude of rare animal and plant species. Rising temperatures are expected to upset this fragile balance, with detrimental effects on the biodiversity that has flourished here for centuries.

Honduras

The most mountainous country in Central America, Honduras contains some of the world’s richest land for growing coffee and bananas, vital exports for this poor nation. In 1998, Hurricane Mitch killed nearly 6,000 people, obliterated much of the country’s infrastructure, and destroyed crops. Three other hurricanes have since surpassed Mitch in severity.