Yale Environment 360: A new analysis of tree-ring data indicates that the climate cycle known as the El Nio Southern Oscillation (ENSO) has been more active during the latter part of the 20th century than at any other time during the past seven centuries, suggesting that global warming is affecting this climate phenomenon. Using data from 2,222 tree-ring chronologies from the tropics and mid-latitudes in both the northern and southern Hemispheres, a team of scientists determined that ENSO-related behavior in the late...