The earth is currently in one of its cyclical global warmings, directly following the Little Ice Age. In the recent past, such warmings have lasted from 350 years (the Medieval Warming) to 800 years (The Roman Warming),” Avery Writes. “Even during this global warming, however, the temperature of the Pacific will cool periodically. The earth will then also cool as the Pacific is the world’s largest heat sink. NASA satellites reported that PDO began to shift cool about 2003, which would mean that cooling will probably last until roughly 2033.