The Identification of 10- to 20-Year Temperature and Precipitation Fluctuations in the Contiguous United States

A potentially fruitful approach to assessing society's sensitivity to climate change is to study the impacts, perceptions and adjustments of recent climate fluctuations. We set out to determine if the recent (1931–82) United States climate record exhibits fluctuations of sufficient scope and magnitude to be useful in a complement of retrospective, empirical studies of climate impacts. The search for fluctuations was designed specifically to identify areas and periods in which the climate within an epoch was terminated by a rather sharp transition to another epoch with a climate unlike the previous epoch. The largest 10- to 20-year temperature and precipitation climate fluctuations were identified across the contiguous United States, along with various scenarios of simultaneous change of temperature and precipitation for the four seasons and annually. All possible 10- to 20-year nonoverlapping “consecutive epochs” within 344 state climatic divisions (as defined by the National Climatic Data Center) were examined for the greatest temporal differences of temperature and precipitation. Additionally, large spatial gradients of climate fluctuations of opposite sign have been identified across climate divisions within short distances of each other (<750 km). The climate fluctuations were specifically identified for the purpose of studying and modeling climate impacts, but they are also of general interest to researchers investigating the physical behavior of climate across the United States. On a seasonal basis our results indicate that over the past half century the most significant and widespread climate fluctuations for temperature of 10–20 years duration, in terms of standardized departures, have been associated with temperature changes of 2°C or more during the winter and summer seasons. Precipitation fluctuations of 25% or more have been detected for similar durations. A partial analog to the current prediction of climate change due to a doubling of CO2 concentration was also identified, namely, an increase of spring and summer temperature (approximately 1°C) and a decrease in precipitation (20–40%) in the central and northern Great Plains. Relatively large spatial gradients of climate fluctuations were identified for nearby climate divisions with opposite climate fluctuations. These spatial “seesaws” of climate fluctuation may prove particularly useful as experimental controls in the study of climate impact, perception and adjustment. Furthermore, they point up the importance of a dense climatological monitoring network.