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A giant wall of dust rolled through the Phoenix area on Thursday for the third time since early July — turning the sky brown, creating dangerous driving conditions and delaying some airline flights. The dust storm, also known as a haboob in Arabic and around Arizona, swept through Pinal County and headed northeast, reaching Phoenix at about 6 p.m. Some incoming and departing flights at Phoenix Sky Harbor International Airport were temporarily delayed because of the storm, according to airport officials who couldn’t immediately provide exact numbers. Take-offs and landing began again at about 6:50 p.m. National Weather Service meteorologists said a powerful thunderstorm packing winds of up to 60 mph hit Pinal County and pushed the dust storm toward Arizona’s most populous county. There were several reports of downed poles and Salt River Project officials said 3,500 of its customers were without electricity, mostly in the Queen Creek area southeast of Phoenix. There were no immediate reports of any weather-related auto accidents. It was the third major dust storm to hit the Phoenix metro area since last month. A haboob on July 5 brought a mile-high wall of dust that halted airline flights, knocked out power for 10,000 people and covered everything in its path with a thick sheet of dust. Another dust storm hit July 18 reaching heights of 3,000 to 4,000 feet, delaying flights and cutting off power for more than 2,000 people in the Phoenix metro area. Weather officials say haboobs only happen in Arizona, the Sahara desert and parts of the Middle East because of dry conditions and large amounts of sand. –The Chron

Fresh snow bounces back 84 percent of the light that hits it; warm, rounded crystals can reflect as little as 70 percent. Slushy snow saturated by water – which gives it a gray cast, or even a bluish tint – reflects as little as 60 percent. Add dust or soot, and the albedo drops below 40 percent. Box's satellite data has shown a steady darkening in Greenland's albedo, from a July average of 74 percent when the century began to about 68 percent last year. And then came this summer: Without warning, the line on the albedo chart dropped deep into uncharted territory. At certain altitudes, the ice sheet in Greenland was suddenly four percent less reflective – in a single season.

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.