Himalayan Glaciers Have Been Losing Ice About Twice as Fast Since 2000, and India Has Measured Them Since 1974, Mapped 28,043 Glacial Lakes From Orbit and Now Watches Two Sikkim Lakes in Real Time

Of the 302 annual measurements taken on 38 Himalayan glaciers since 1974, 270 show the glacier losing mass and 32 show it gaining, according to a 2026 review in the Journal of Glaciology by Mohd Farooq Azam of ICIMOD and the Indian Institute of Technology Indore. The first of those measurements was taken by the Geological Survey of India (GSI) on Gara Glacier in Himachal Pradesh in June 1974.

The sources below agree on the direction of change. They differ on how fast, on the Karakoram range and on how much ice will be left in 2100, and each range is given here with the study that produced it.

What the stakes on Gara Glacier started

Mass balance is the net gain or loss of snow and ice over a glacier’s surface in a year, written in metres of water equivalent (m w.e.), as if all of it were melted. On Gara, a 5.2 square kilometre glacier, GSI’s 1974 expedition set 34 stakes in the melting zone and 13 in the snow-gaining zone to track melt and snowfall, Azam’s review records.

Across all 38 glaciers in the compilation, the average loss was 0.62 m w.e. a year, with an uncertainty of 0.33. Added up over 1974 to 2023, that is 23.95 m w.e. of loss, give or take 1.44. The yearly loss was 0.31 m w.e. before 2000 and 0.66 afterwards, which Azam puts at an acceleration of 9 cm w.e. per decade.

Indian sites hold both the first record and the longest continuous one. Chhota Shigri Glacier in Himachal Pradesh has the longest running series in the Himalaya, 21 years from 2002 to 2023, with a loss of 0.47 m w.e. a year. It and Hoksar in the Jhelum basin are two of the seven glaciers that meet the World Glacier Monitoring Service’s definition of a benchmark glacier. The other five are in Nepal.

Other agencies add their own stations. The National Centre for Polar and Ocean Research (NCPOR) has monitored six glaciers in the Chandra basin since 2013 and runs the Himansh field station there, operating since 2016. The Ministry of Earth Sciences told the Rajya Sabha on 20 July 2023 that the basin has lost about 6 percent of its glacier area in 20 years and that its glaciers retreat 13 to 33 metres a year. The Wadia Institute of Himalayan Geology (WIHG) reports that Dokriani Glacier in the Bhagirathi basin of Garhwal retreats 15 to 20 metres a year. A Rajya Sabha reply of 25 July 2024 adds that GSI has measured mass balance on nine glaciers and studied the advance or retreat of 90. The Earth Sciences ministry’s parliamentary reply of 3 December 2025 says more than 20 institutions, from IISc to Sikkim University, now study Himalayan glaciers.

Azam lists the gaps himself. Seventeen of the 38 series have stopped, including Gara’s, and he says many ended because GSI ran its monitoring in mission mode. No Himalayan series has the 30 years that the world monitoring service requires for a reference glacier. He names Sikkim among the regions that need more stations.

Field stakes against satellite height maps

A second method compares elevation models of the same glaciers taken years apart. Maurer and colleagues did this in Science Advances in 2019 for 650 glaciers larger than about 3 square kilometres, using declassified Cold War spy-satellite film for the first period and modern stereo imagery for the second. The loss averaged 0.22 m w.e. a year over 1975 to 2000 and 0.43 over 2000 to 2016, a doubling, with uncertainties of 0.13 and 0.14. They saw ice loss along the whole 2,000 km range in both periods.

The field series and the satellite work land close together on the total. A 2025 satellite-based dataset by Dussaillant and colleagues, read for the same 38 glaciers, gives a cumulative loss of 23.60 m w.e. for 1974 to 2023, against 23.95 from the stakes. They part on the yearly average, 0.48 against 0.62 m w.e.

Azam gives a reason. A stake network can overstate loss when a glacier has no developed snow-gaining area to measure. On Hamtah Glacier the stakes gave 1.43 m w.e. a year over 2000 to 2012 against 0.68 from the satellite dataset, and he advises reading the 0.62 average with caution.

ICIMOD, the Kathmandu centre whose eight member countries include India, covered the wider Hindu Kush Himalaya in its 2023 report. It finds that the loss rate rose 65 percent, from 0.17 m w.e. a year in 2000 to 2009 to 0.28 in 2010 to 2019, with high confidence. Its press release called the changes in the region’s glaciers, snow and permafrost “unprecedented and largely irreversible.”

The Karakoram exception, and whether it still holds

The Karakoram, the range in the north-west that holds 48 percent of the Himalaya-Karakoram glacier area, long behaved differently. The 2019 Hindu Kush Himalaya Assessment says glaciers in the Karakoram, eastern Pamir and western Kunlun had balanced mass budgets or slight gains since at least 2000, a pattern named the Karakoram anomaly.

The 2023 report says that has ended, with medium confidence. It gives the Karakoram a loss of 0.09 m w.e. a year, with an uncertainty of 0.04, for 2010 to 2019.

The Earth Sciences ministry’s replies give the Karakoram an average shortening of 1.37 metres a year with a spread of 22.8, and its 2023 reply read that as stable conditions. Its December 2025 reply adds that the figure after the plus-or-minus sign is a standard deviation. Azam adds that no glacier-wide measurement with stakes has been made in the Karakoram. The only field work on record is on the melting zone of Baltoro Glacier in 2004.

How much ice is left in 2100 depends on who counts

The projections differ by region, model and emissions scenario. The 2019 assessment’s chapter on the cryosphere covers an extended region that includes the Pamirs, Tien Shan and Tibetan Plateau. It projects volume losses of more than one-third for those glaciers even if warming stops at 1.5 degrees Celsius, and more than half in the eastern Himalaya. Its key findings say volumes could fall by up to 90 percent through the 21st century, and that lower emissions would reduce the loss.

The 2023 report, which covers the Hindu Kush Himalaya itself, gives a volume loss of 30 to 50 percent by 2100 if warming stays below 2 degrees and 55 to 80 percent at higher warming. ICIMOD’s press release led with the top of that range: up to 80 percent on current emissions trajectories.

Rivers are harder to project than ice. The 2023 report says water in the region’s rivers should peak around mid-century and decline after, and that confidence in estimates of future run-off remains low because rainfall projections are uncertain. It puts rainfall run-off at 50 to 79 percent of the flow in rivers such as the Ganges and Brahmaputra, a share it ties to the summer monsoon. The National Institute of Hydrology has recorded flow at Bhojwasa, below Gaumukh, since 2000, and the ministry says the volume shows little variation.

28,043 lakes, counted from orbit

Melting ice fills new lakes, and India has counted them from space. The National Remote Sensing Centre (NRSC) of ISRO mapped 28,043 glacial lakes across the Indian Himalayan river basins from Resourcesat-2 images, 93 percent of them above 4,000 metres. About 27 percent lie inside India and the rest in neighbouring territory. NRSC then picked 15 lakes for flood modelling.

ISRO’s analysis of 1984 to 2023 imagery, released on 22 April 2024, looked at the 2,431 lakes larger than 10 hectares. It found that 676 had expanded sharply since 1984 and that 601 of those had more than doubled. Of the 676, 130 are inside India: 65 in the Indus basin, 7 in the Ganga and 58 in the Brahmaputra. Ghepang Ghat lake in Himachal Pradesh grew from 36.49 to 101.30 hectares between 1989 and 2022.

The National Disaster Management Authority (NDMA) has ranked 195 potentially high-risk lakes across Himachal Pradesh, Uttarakhand, Sikkim, Arunachal Pradesh, Jammu and Kashmir and Ladakh. A Himachal study cited in its affidavit counts lakes in the Satluj catchment rising from 562 in 2019 to 1,048 in 2023. ICIMOD’s report deems 200 glacial lakes across the whole region dangerous.

Whether outbursts themselves are becoming more frequent is not settled. The 2023 report finds limited evidence of a rise in the number of glacial lake outburst floods (GLOFs) in recent decades, with high confidence, while projecting a threefold rise in GLOF risk by the end of the century. The 2019 assessment also called the trend unclear.

Not every lake is growing. NRSC’s assessment of Shako Cho in North Sikkim, a lake at 4,960 metres holding about 15.66 million cubic metres, found little change in its area over six decades, although its loose moraine dam and the village 10 km downstream made it worth modelling.

The night of 3 October 2023 at South Lhonak Lake

South Lhonak Lake sits at 5,200 metres in the upper Teesta basin. At 10:12 pm on 3 October 2023, about 14.7 million cubic metres of frozen moraine slid off its northern bank into the water, Sattar and 33 co-authors report in Science. The slide came from a slope 900 metres wide and 88 metres thick. It raised a wave of about 20 metres that cut a breach 165 metres wide and 55 metres deep through the lake’s front moraine.

About 50 million cubic metres of water left the lake, roughly half of it, and its level fell about 28 metres. The flood reached an Indo-Tibetan Border Police camp 7 km downstream around 10:30 pm and Chungthang, where the 1,200 MW Teesta III dam stood, around 12:30 am on 4 October. The authors put its peak discharge far above rain-fed flood levels in the region, equal to a return period beyond 200 years.

The study counts 55 deaths, 74 missing and more than 7,000 displaced across 100 villages, from a survey by a team the Sikkim State Disaster Management Authority set up. The flood destroyed Teesta III and damaged four more dams, 31 major bridges and about 25,900 buildings along its path. It set off 45 landslides, and eroded around 270 million cubic metres of sediment along the valley. It travelled 385 km into Bangladesh, where more than 17,000 of the damaged buildings stood. The Sikkim side of that history, including the debate over rebuilding the dam, is in our profile of the state.

ISRO’s analysis, dated 4 October 2023, compared a RISAT-1A image from 6 am that day with a Sentinel-1A image of 28 September. It found that about 105 hectares of the lake had drained.

The authors found no cloudburst. Rain over the lake from 28 September to 5 October totalled 29 to 39 mm, typical for the season. They attribute the collapse to a slope that moved at more than 15 metres a year between 2016 and 2023, tracked across 257 pairs of satellite images, to warming of the frozen ground down to about the depth where the slide detached, and to a lake that grew by up to 100 metres a year as the glacier lost mass.

The lake had been on the hazard list. Sattar and colleagues describe it as one of the largest, fastest-growing and most hazardous in Sikkim. The Swiss company Geopraevent says the outburst came 17 days after it installed the first monitoring system there. Reuters reported on 11 October 2023 that a planned 2022 expedition to the lake could not be organised in time. NDMA member Krishna S. Vatsa told it that the lake can be reached only from July to September and that the border area needed clearances.

The Ministry of Environment’s Rajya Sabha reply of 25 July 2024 lists four glacier-related disasters from state and expert inputs: Uttarakhand in 2013 and 2021, Ladakh in 2021 and Sikkim in 2023. The June 2013 floods in Uttarakhand, including the collapse of Chorabari Lake, are covered in our piece on the Char Dham routes.

What has been installed since

NDMA issued national guidelines on managing GLOFs in October 2020. After South Lhonak it formed a Committee on Disaster Risk Reduction with DRDO, the Central Water Commission, GSI, the India Meteorological Department, NRSC and other bodies, which meets monthly with states.

The National GLOF Risk Mitigation Programme, with Rs 150 crore (about Rs 1.5 billion) approved by the Ministry of Home Affairs, covers Arunachal Pradesh, Himachal Pradesh, Uttarakhand and Sikkim, and the ministry’s December 2025 reply adds Jammu and Kashmir and Ladakh. NDMA says states and union territories have run more than 30 expeditions under it, using depth surveys, ground-penetrating radar and drone mapping.

At South Lhonak and Shako Cho, the Sikkim authority, NDMA and the Swiss Agency for Development and Cooperation installed weather and water stations, and the Earth Sciences ministry’s December 2025 reply says both lakes are now monitored in real time. NDMA and C-DAC have put a GLOF early-warning system on trial in Lahaul and Spiti for validation, and plan to move its sensors to Ghepang Ghat lake (spelled Ghephang Gath in the affidavit). The Department of Science and Technology has set up glacier research centres of excellence at the universities of Sikkim, Tezpur and Kashmir, and the National Institute of Hydrology opened a cryosphere centre at Roorkee in 2023.

NDMA’s affidavit of 2 July 2026 lists further steps for the Green Tribunal to consider: extending the programme to more river basins, requiring GLOF assessments in project approvals, and real-time monitoring and early warning at every priority lake. At South Lhonak, Sattar and colleagues measured a patch of the collapse scarp about 0.5 by 0.3 km still moving at up to 15 metres a year between October 2023 and June 2024.