Yale Himalaya Initiative

environment | livelihood | culture

638 years of summer temperature variability over the Bhutanese Himalaya

By:Peter Jang - On Tuesday evening, Edward R. Cook, Director of the Tree-Ring Lab at Columbia University, presented his recent study on climate change in Bhutan and the greater Himalayas. With the help of Paul Krusic (Stockholm University) and local Bhutanese researchers, Professor Cook established a dendrochronological network comprised of twelve locations throughout Bhutan dating back to 2002. Using data collected from Himalayan spruce (Picea spinulosa) from two sites in their network, the project’s team has traced summer temperature variability over the Bhutanese Himalaya from 1376-2013, an interval of 638 years.

In their reconstructed chronology, the team identified two prominent cold periods in the mid-15th and late-17th centuries, lasting a span of ten and twenty-five years respectively. Each of these periods was marked by above-average temperatures in the summers. Worryingly, the warmest summer temperatures in the timescale have been recorded in the first decade of the 21st century, a phenomenon consistent in timing with rapid glacier retreat in Bhutan and its surrounding regions. Bhutan continues to struggle with melting glaciers, which pose immediate threats to valleys and low lying river plains from glacier lake outburst flood (GLOF) hazards.

The study also found a strong correlation of high-temperature fluctuations following volcanic activity and medium-temperature fluctuations during periods of reduced solar irradiance. As such, the findings suggest that solar variability over the region also affect temperature levels in addition to byproducts of human involvement (e.g. greenhouse gases).

The region-specific temperature chronology tells the broad story of the gradual, yet consistent increase in the Earth’s average surface temperature in recent decades. What distinguishes Professor Cook’s reconstruction from those of other dendrochronological studies is its focus on Bhutan, which permits more locally optimal climate change and glacier modeling studies for the future.

Professor Cook concluded his talk with an open invitation to the 10th World Dendro Conference held from June 11-15, 2018 in Thimpu, Bhutan.