If society continues to pump greenhouse gases into the atmosphere at the current rate, Americans later this century will have to endure, on average, about 15 daily maximum temperature records for every time that the mercury notches a record low, new research indicates.That ratio of record highs to record lows could also turn out to be much higher if the pace of emissions increases and produces even more warming, according to the study led by scientists at the National Center for Atmospheric Research (NCAR).