Despite the seemingly endless deluge of Starbucks coffee shops that have cropped up globally, tea is still more popular than coffee; it's the second most consumed beverage after water. Though all teas come from the same plant—a bush called Camellia sinensis—Darjeeling has long been regarded as one of the most delicate and sought-after of teas, grown and harvested by hand rather than by machinery, and produced at elevation in the terroir of the Himalayas.

But that careful ecosystem is under threat, as are the jobs of workers, who already make dismal wages of less than $1.50 a day. "Glaciers are receding. Daily temperatures have risen, nights don't cool as they once did, and a sudden hailstorm can batter a hillside of tea bushes with ice. Particularly problematic is the erratic and unpredictable monsoon," Jeff Koehler, a Seattle-based author, wrote in one of the most comprehensive books on Darjeeling.