Scientific American: From the 1940s through the 1970s there was no major warming trend in the average surface temperature of Earth. At the same time, the tropical Pacific Ocean, which is responsible for the weather patterns known as El Nio and La Nia that can swing global average temperatures by as much as 0.3 degree Celsius, was anomalously cold. For the past decade or so the tropical Pacific has again gone cold--more Nia than Nio--and a new study suggests that the phenomenon may explain the recent "pause" in global...