|Title||Temperature reconstructions spanning the Continental Divide: Bristlecone and limber pine trees as proxy data|
|Year of Publication||1998|
|University||Arizona State University|
|Keywords||Bristlecone, Continental divide, Limber pine, Pinus, Temperature reconstructions|
Variability in the intensity and magnitude of the Pacific North American (PNA) circulation pattern and the reverse-PNA affects high and low frequency temperature variations on either side of the Continental Divide, on the Colorado Plateau. The PNA circulation pattern corresponds with cooler temperatures on the Colorado Plateau, whereas the reverse-PNA circulation pattern corresponds with warmer temperatures on the Colorado Plateau associated with a high pressure ridge over the Rocky Mountains.
Temperature was reconstructed using three Pinus aristata (bristlecone pine) chronologies and one Pinus flexilis (limber pine) chronology from subalpine sites located on either side of the Continental Divide in Colorado and Arizona. The standardized ring-indices of the four chronologies (scAD 548-1994) were correlated with historic temperature data from twelve ground stations and upper air temperature data from four radiosonde stations in Arizona, Colorado, New Mexico and Utah.
Temperature reconstructions across a transect spanning the Continental Divide on the Colorado Plateau provide valuable insight to temporal changes in large scale circulation patterns. Reconstructions of annual temperature indicate there were several periods when temperatures were below the modern mean east of the Continental Divide when they were above the modern mean west of the Continental Divide. Variability in the direction of temperature change on either side of the Continental Divide may reflect a westward displacement of the high pressure ridge at different times in history. Reconstructions of annual temperature also indicate 850 mb temperature east of the Divide is slightly higher when the PNA circulation pattern occurs as a teleconnection to El Nino Southern Oscillation (ENSO) events. In contrast, annual 700 mb temperature west of the Divide is slightly lower.
Temperature reconstructions also indicate higher mean annual temperatures occurred between scAD 550 to 600, scAD 900-980, and scAD 1040-1080, and scAD 1130-150 than between 1950 and the present. These reconstructions suggest low frequency cycles of above average temperatures have occurred throughout history. These results indicate more research is required to determine whether recent warming trends identified by other researchers reflect anthropogenic warming or natural cycles.