Himalayan glacier mass loss up to 267% higher after 2000: Study

Dehradun: Glaciers across the Himalaya-Karakoram, often referred to as the "Third Pole" for holding the largest ice reserves outside the Arctic and Antarctic, have seen mass loss accelerate sharply since 2000 -- by 17% to 267% in some of these -- compared to the second half of the 20th century, according to a new seven-decade study of five glaciers. Together, the Himalaya and Karakoram host the world's largest concentration of mountain glaciers outside the polar regions, spanning about 42,500 sq km.The study, titled ‘Seven Decades of Mass Balance Change in Selected Large Himalayan and Karakoram Glaciers: Climatic Drivers and Regional Contrasts', reconstructs glacier-wide mass balance between 1950 and 2022 for five major glaciers: Baltoro and Siachen in the Karakoram, and Bara Shigri, Gangotri and Zemu in the Himalaya. Together, these glaciers cover around 2,300 sq km, which is about 5.5% of the glacierised area of the Himalaya-Karakoram region.Researchers from the International Centre for Integrated Mountain Development, Nepal, Indian Institute of Technology Indore and the University of Aberdeen, Scotland, found that glacier mass loss intensified markedly after 2000. "In simple terms, glaciers that were already losing ice began losing it much faster," the study said.According to the research, among the Himalayan glaciers, Gangotri -- which is one of the largest glaciers feeding the Ganga basin -- showed a "consistently negative mass balance" over the entire 70-year period, indicating "sustained and substantial ice loss". Bara Shigri and Zemu glaciers also recorded negative mass balances, reflecting "long-term thinning and retreat".In contrast, the Karakoram glaciers -- Baltoro and Siachen -- remained broadly close to balance over the full study period, with near-neutral to slightly positive mass balance conditions overall. However, even these glaciers shifted towards more negative balances after 2000, suggesting that the "long-observed stability in parts of the Karakoram may be weakening", though researchers cautioned that "evidence is not yet conclusive".Glacier mass balance refers to the difference between winter snow accumulation and summer melt, and serves as a key indicator of glacier health and climate response. A positive balance means accumulation exceeds loss and a negative balance indicates the reverse. As per the research, the acceleration in ice loss coincided with rising temperatures across all five glaciers and generally declining precipitation. In the eastern Himalaya, precipitation increased, but largely as rainfall rather than snowfall, limiting its contribution to glacier build-up.The study also highlighted clear regional contrasts, finding that Himalayan glaciers are more sensitive to temperature changes, while snow variability plays a stronger role in influencing glacier behaviour in the Karakoram. It noted that over time, temperature has emerged as the dominant driver of mass loss across much of the Himalaya."Overall, the findings point to a common trend despite regional differences: glacier systems across the Himalaya-Karakoram are losing mass faster in the 21st century than in the preceding five decades, with significant implications for long-term water security in glacier-fed river basins," the authors warned, emphasising that "there is a critical need for in-depth study and continuous monitoring of Himalaya-Karakoram glaciers' responses to ongoing climate change at the glacier scale."