The primary goal of the annual State of the Climate collection of articles is to document the weather and climate events in 2009 from around the world and put them into accurate historical perspective, with a particular focus on unusual or anomalous events. In total, 37 Essential Climate Variables were reported in 2009.

The role of the tropics in triggering, transmitting, and amplifyinginterhemispheric climate signals remains a key debate in paleoclimatology.Tropical glacier fluctuations provide important insight on regionalpaleoclimatic trends and forcings, but robust chronologies arescarce.