How does the cryosphere affect global climate?

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Ghissu Editorial · Accepted Answer

The cryosphere regulates global climate by reflecting sunlight, driving the thermohaline circulation and storing water and carbon, and its melting turns it into an amplifier of warming. The Arctic has warmed nearly four times faster than the globe since 1979 as retreating ice exposes darker surfaces.

**Introduction**

The cryosphere, made of sea ice, ice sheets, glaciers, snow and permafrost, is the planet's mirror, pump and vault: it reflects sunlight, drives deep ocean circulation and locks away water and carbon.

**How the Cryosphere Regulates Climate**

SKETCH: tree | Cryosphere's climate roles
- Reflects heat
  - Ice-albedo effect
- Moves heat
  - Deep ocean currents
- Stores water, carbon
  - Sea level, permafrost

1. **Planetary mirror**: Fresh snow reflects up to about 80-90% of sunlight against roughly 6% for open ocean, sustaining the temperature gradient that drives winds and jet streams.
2. **Engine of deep currents**: Salt rejected by forming sea ice makes dense water that sinks off Antarctica and in the North Atlantic, powering the thermohaline circulation that carries heat poleward.
3. **Vault of water and carbon**: Ice sheets hold about 65 m of potential sea-level rise and permafrost about 1,500 billion tonnes of carbon (IPCC SROCC, 2019).
4. **Monsoon link**: Heavy Eurasian and Himalayan snow delays land heating and can weaken India's monsoon, a link Blanford used in the 1880s.

**A Melting Cryosphere Feeding Back on Climate**

1. **Arctic amplification**: Retreating ice exposes darker surfaces, so the Arctic has warmed nearly four times faster than the globe since 1979 (Rantanen et al., 2022).
2. **Wavier jet stream**: A weaker temperature contrast is linked, though debated, to stalled heatwaves and cold spells.
3. **Slowing conveyor**: Greenland meltwater has pushed the Atlantic overturning circulation to its weakest in over a millennium (Caesar et al., 2021).
4. **Thawing permafrost**: Thaw releases carbon dioxide and methane, a self-reinforcing loop.

**Conclusion**

By cooling the Earth, moving its heat and storing its water and carbon, the cryosphere stabilises global climate, and its loss turns it into an amplifier of warming. Keeping warming near 1.5°C under the Paris Agreement is the surest way to avoid crossing its tipping points.

How does the cryosphere affect global climate?

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