But the future, pressing as it is, sometimes gives way to sheer awe at the scale of what we've already done. Simply by changing the albedo of the Greenland ice sheet, Box calculates, the island now absorbs more extra energy each summer than the U.S. consumes in a year. The shape and color of the ice sheet's crystals, in other words, are trapping more of the sun's rays than all the cars and factories and furnaces produce in the world's biggest economy. One of Box's collaborators, photographer James Balog, puts it like this: "Working in Greenland these past years has left me with a profound feeling of being in the middle of a decisive historic moment – the kind of moment, at least in geologic terms, that marks the grand tidal changes of history." Amid this summer's drama of drought, fire and record heat, the planet's destiny may have been revealed, in a single season, by the quiet metamorphosis of a silent, empty sheet of ice.