The kingdom of Bhutan, famous for maximizing "Gross National Happiness" rather than GDP, is sitting under a gigantic time bomb of water that could burst at any moment, flooding its villages and putting a major damper on all that good cheer.

Bhutan has 2,674 glacial lakes, 24 of which are considered unstable. When the ice dams holding them back burst — as happened in 1994, killing dozens — they lead to "mountain tsunamis."

Long-term, the bigger danger isn't too much water, but too little. Forty percent of the country's wealth comes from its hydroelectric dams, and its farmers rely on its rivers to irrigate their crops. As the glaciers at the top of the world dwindle, Bhutan will be one of the first countries to experience ill effects — along with the billions of people in China and India who rely on rivers that originate in the Himalayas.