Using modern time series analysis we discover a characteristic time scale in the global temperature record. This time scale corresponds to about 20 months and separates processes that promote a trend in the past from processes that reverse this tendency. This characteristic scale has important implications one of which might be that the El Ni¿o/La Ni¿a cycle may act as a mechanism countering the tendency of shorter time scale events to organize a positive or a negative temperature trend. ¿ 1998 American Geophysical Union