Glacial Retreat: The interactive image above illustrates nearly a century's worth of changes to the Rongbuk Glacier in the Himalaya of southern Tibet. The black and white photo was taken in 1921 by George Mallory of the Royal Geographical Society. The color photo was taken from the same position in 2007 by David Breashears, Executive Director and Founder of Glacier Works, a non-profit organization that uses "art, science and adventure" to highlight changes to Himalayan glaciers. Use the scroll bar to swipe back and forth across the image to see the difference. And listen the Marketplace interview with Breashears.