Are Karakoram temperatures out of phase compared to hemispheric trends?

In contrast to a global retreating trend, glaciers in the Karakoram showed stability and/or mass gaining during the past decades. This “Karakoram Anomaly” has been assumed to result from an out-of-phase temperature trend compared to hemispheric scales. However, the short instrumental observations from the Karakoram valley bottoms do not support a quantitative assessment of long-term temperature trends in this high mountain area. Here, we presented a new April–July temperature reconstruction from the Karakoram region in northern Pakistan based on a high elevation (~3600 m a.s.l.) tree-ring chronology covering the past 438 years (AD 1575–2012). The reconstruction passes all statistical calibration and validation tests and represents 49 % of the temperature variance recorded over the 1955–2012 instrumental period. It shows a substantial warming accounting to about 1.12 °C since the mid-twentieth century, and 1.94 °C since the mid-nineteenth century, and agrees well with the Northern Hemisphere temperature reconstructions. These findings provide evidence that the Karakoram temperatures are in-phase, rather than out-of-phase, compared to hemispheric scales since the AD 1575. The synchronous temperature trends imply that the anomalous glacier behavior reported from the Karakoram may need further explanations beyond basic regional thermal anomaly.