The changing cryosphere

The first principle

Ice matters to climate for two physical reasons. It is bright, so it reflects sunlight that dark ocean or rock would absorb, and it stores water, so its melting moves mass between land and sea. Everything in this note, from Arctic shipping to the flow of the Indus, follows from where the ice sits: floating on the sea, resting on land, or frozen into the ground.

The core

What the cryosphere is

• The cryosphere is all frozen water on Earth: sea ice floating on the polar oceans, the ice sheets of Greenland and Antarctica, mountain glaciers, permafrost (ground frozen for at least two years) and seasonal snow cover. Ice sheets hold about two thirds of the world's fresh water.

How the cryosphere affects global climate

• Albedo. Fresh snow reflects about 80 to 90 per cent of sunlight and sea ice about 60 per cent, while open ocean reflects under 10 per cent. When ice gives way to water, the surface absorbs several times more energy.
• Ice albedo feedback. That extra absorbed energy melts more ice, which lowers albedo further, so a small initial warming is amplified; this is a positive feedback.

• Arctic amplification. Because of this feedback, and because heat that the open ocean absorbs in summer is released to the air in autumn, the Arctic has warmed about three to four times faster than the global average since 1979.
• Sea level. Melting land ice and the thermal expansion of warmer seawater raise sea level; the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC, 2019) projected a rise of about 0.3 to 0.6 m by 2100 with low emissions and 0.6 to 1.1 m with high emissions.
• Ocean circulation. Sinking of cold, salty, dense water in the North Atlantic and around Antarctica drives the thermohaline circulation, the deep ocean conveyor. Fresh meltwater is lighter, so it caps the surface, weakens sinking, and slows the transport of heat from the tropics to the poles.
• Permafrost carbon. Permafrost holds roughly 1,500 billion tonnes of carbon, about twice what is in the atmosphere now; when it thaws, microbes release carbon dioxide and, in waterlogged soil, methane, which adds warming without any new human emission.
• Jet stream. The jet stream is driven by the temperature contrast between the pole and the tropics. A warmer Arctic reduces that contrast, and some studies link this to a weaker, wavier jet that lets cold spells and heat waves stall over mid latitudes; this link is still debated among scientists.

Dimensions

Arctic sea ice and Antarctic land ice: different melts, different effects

The Arctic is an ocean ringed by land, so most of its ice floats; Antarctica is a continent ringed by ocean, so most of its ice sits on rock up to 4 km thick. By Archimedes' principle a floating body displaces its own weight of water, so when sea ice melts the water it becomes fills almost exactly the hole it made. Land ice adds new water to the ocean.

• Arctic sea ice melt changes weather and human activity more than sea level. September sea ice extent has fallen by about 13 per cent a decade since satellite records began in 1979, which amplifies Arctic warming, may disturb the jet stream, opens summer shipping routes, and makes oil, gas, minerals and fisheries reachable. It also destroys the hunting and travel surface on which Inuit and other Arctic peoples depend.
• Antarctic and Greenland land ice melt raises sea level directly; Greenland holds enough ice to raise it about 7 m and Antarctica about 58 m. The main risk comes from West Antarctica, where glaciers such as Thwaites rest on bedrock below sea level, so warm water eating under them can trigger retreat that feeds on itself. Fresh meltwater around Antarctica also slows the overturning of the Southern Ocean, which takes up a large share of the heat and carbon that humans add.
• The ozone hole link. The Antarctic ozone hole cooled the upper atmosphere over the pole and strengthened and shifted the Southern Hemisphere westerly winds southwards in summer, which has altered rainfall in places such as south western Australia; ozone recovery under the Montreal Protocol is expected to slowly reverse this.

In practice

The Himalayan glaciers and India's water

The Hindu Kush Himalaya holds the largest store of ice outside the poles, which is why it is called the Third Pole. The International Centre for Integrated Mountain Development (ICIMOD) Hindu Kush Himalaya Assessment (2019) projected that one third of its glacier volume would be lost by 2100 even if warming were held to 1.5°C, and up to two thirds under high emissions. Its 2023 update found that glaciers lost mass 65 per cent faster in 2011 to 2020 than in the previous decade.

• Peak water. As glaciers melt faster, river flow first rises, then falls once the ice store shrinks; most Himalayan basins are expected to reach this peak around the middle of the century, after which dry season flow declines.
• Unequal dependence. The upper Indus gets most of its flow from snow and glacier melt, while the Ganga and Brahmaputra depend more on monsoon rain, so the Indus plains of Punjab, Haryana and Ladakh face the largest risk to irrigation and drinking water in the dry months before the monsoon.

• Hazards. Retreating glaciers leave lakes dammed by loose moraine; when a moraine fails, a glacial lake outburst flood (GLOF) follows. In October 2023 South Lhonak lake in Sikkim burst and destroyed the Chungthang dam of the Teesta III hydropower project, and in February 2021 a rock and ice avalanche in Chamoli, Uttarakhand, sent a flood that wrecked the Rishiganga and Tapovan Vishnugad projects and killed about 200 people.
• Response. The National Disaster Management Authority (NDMA) issued GLOF guidelines in 2020 and later began a programme to monitor and lower the risk at nearly 190 high risk glacial lakes. The National Mission for Sustaining the Himalayan Ecosystem, under the National Action Plan on Climate Change (NAPCC), funds glacier monitoring.

Why India takes a keen interest in the Arctic

• Science and the monsoon. Arctic warming may influence the Indian monsoon through changes in atmospheric circulation, so India studies it at Himadri, its research station at Ny Alesund in Svalbard, and through the IndARC ocean observatory.
• Resources. The United States Geological Survey (USGS, 2008) estimated that the Arctic holds about 13 per cent of the world's undiscovered oil and 30 per cent of its undiscovered gas, besides rare earths, other minerals and fisheries. ONGC Videsh, the overseas arm of the Oil and Natural Gas Corporation, holds a stake in Russia's Vankor oil field, and India wants a share in energy that is less exposed to the Strait of Hormuz.
• Shipping. The Northern Sea Route along Russia's coast cuts the Europe to East Asia voyage by roughly a third compared with the Suez route, and India and Russia have discussed cooperation on it alongside the Chennai Vladivostok maritime corridor.
• Strategy. China calls itself a "near Arctic state", plans a Polar Silk Road and holds stakes in Russia's Yamal LNG project, so India's presence keeps a seat at the table where rules for the region are written.

India's Arctic Policy (Ministry of Earth Sciences, March 2022) rests on six pillars, from science and climate protection to economic development, connectivity, governance and national capacity.

Issues and way forward

• Data gaps in the Himalaya. Few glaciers have long field records because high altitude work is costly; the ICIMOD assessments and the Ministry of Earth Sciences recommend more benchmark glaciers and shared data among Himalayan countries.
• Hydropower in the path of floods. Projects are built on valleys where GLOFs and debris flows travel; the NDMA guidelines recommend lake mapping, early warning sensors and controlled lowering of dangerous lakes, as was tried at South Lhonak with siphon pipes in 2016, though on too small a scale to prevent the 2023 burst.
• Planning for less dry season water. Because melt will fall after peak water, the ICIMOD reports recommend storage, groundwater recharge and efficient irrigation in the Indus plains now, rather than after flows decline.
• Arctic opportunity versus Arctic harm. Oil drilling and shipping in the Arctic would add emissions and spill risk in a region that cannot clean up quickly; India's own Arctic Policy commits to responsible use, which means supporting the Polar Code of the International Maritime Organization and the rights of Arctic indigenous peoples.

Common confusions

• Sea ice and ice shelves. Both float, so their melt hardly raises sea level, but ice shelves hold back land glaciers, and their collapse lets that land ice speed into the sea.
• Arctic and Antarctic sea ice trends. Arctic sea ice has fallen steadily since 1979; Antarctic sea ice grew slightly until 2015 and then fell sharply, with record lows in 2023.
• Chamoli 2021 and South Lhonak 2023. South Lhonak was a true glacial lake outburst; Chamoli began as a rock and ice avalanche, not a lake burst.

For the exam

• Keyword bank: albedo, ice albedo feedback, Arctic amplification, thermohaline circulation, permafrost carbon, methane, wavy jet stream, marine ice sheet instability, Thwaites, Third Pole, peak water, GLOF, Northern Sea Route, Himadri, Arctic Policy 2022.
• Previous year questions: Practise the previous year questions on this topic →
• Use in an answer:
  • Introduction (data): Himalayan glaciers lost mass 65 per cent faster in 2011 to 2020 than in the decade before, according to ICIMOD's 2023 assessment.
  • Introduction (judgement, quote or report): The IPCC Special Report on the Ocean and Cryosphere (2019) warned that the loss of ice will raise sea level for centuries even if emissions stop.
  • Conclusion: Floating ice changes the weather and access, land ice changes the coastline, and both demand that mitigation and adaptation advance together.
  • Conclusion: For India the cryosphere is not a distant polar matter; the Himalaya is its water tower and the Arctic is linked to its monsoon, so both deserve sustained science and diplomacy.