Associated Press: Wade McGillis peered up at the structure propped like a high-tech stick figure — minus the head — on an elementary school roof. Then he examined the electronics attached to its spindly metal frame, looking out over the Harlem brownstones nearby and the skyscrapers farther away. Within 15 minutes, a graph spiked in his office eight blocks away. The abrupt peak marked the carbon dioxide the Columbia University environmental engineering professor and three visitors had …