Karakorum temperature out of phase with hemispheric trends for the past five centuries

Abstract

A systematic increase in global temperature since the industrial revolution has been attributed to anthropogenic forcing. This increase has been especially evident over the Himalayas and Central Asia and is touted as a major contributing factor for glacier mass balance declines across much of this region. However, glaciers of Pakistan’s Karakorum region have shown no such decline during this time period, and in some instances have exhibited slight advance. This discrepancy, known as the ‘Karakorum Anomaly’, has been attributed to unusual amounts of debris covering the region’s glaciers; the unique seasonality of the region’s precipitation; and localized cooling resulting from increased cloudiness from monsoonal moisture. Here we present a tree-ring based reconstruction of summer (June–August) temperature from the Karakorum of North Pakistan that spans nearly five centuries (1523–2007 C.E.). The ring width indices are derived from seven collections (six—Picea smithiana and one—Pinus gerardiana) from middle-to-upper timberline sites in the northern Karakorum valleys of Gilgit and Hunza at elevations ranging from 2850 to 3300 meters above mean sea level (mean elevation 3059 m asl). The reconstruction passes all traditional calibration–verification schemes and explains 41 % of the variance of the nested Gilgit–Astore instrumental station data (Gilgit—1454 m asl, 1951–2009; Astore—2167 m asl, 1960–2013). Importantly, our results indicate that Karakorum temperature has remained decidedly out of phase with hemispheric temperature trends for at the least the past five centuries, highlighting the long-term stability of the Karakorum Anomaly, and suggesting that the region’s temperature and cloudiness are contributing factors to the anomaly.