🌡️ Chapter 06 · Topic 02 · Climate Change

Effects of Climate Change

Sea level rise, glacial retreat, extreme weather events, coral bleaching, ocean acidification, species extinction, food security, and India-specific impacts — complete UPSC & PSC notes.

🌊 Sea Level Rise

Sea level rise is one of the most significant and well-documented effects of climate change. It occurs due to two main processes:

Thermal expansion — as ocean water warms, it expands in volume (accounts for ~50% of observed rise)
Glacial and ice sheet melt — melting of mountain glaciers, Greenland Ice Sheet, and Antarctic Ice Sheet adds water to oceans
Current rate: approximately 3.3–3.7 mm per year (accelerating; was ~1.4 mm/year in the 20th century)
Total rise since 1900: approximately 20 cm
Projected rise by 2100: 0.3–1.0 m under various scenarios (could be higher if ice sheets destabilise)

⭐ Countries Most at Risk: Maldives (average elevation ~1.5 m — could be uninhabitable by 2100), Tuvalu (Pacific island nation — already signing agreements for relocation), Bangladesh (17% of land area could be submerged; 20 million people displaced), Kiribati, Marshall Islands. India’s coastal cities at risk: Mumbai, Chennai, Kolkata, Kochi, Visakhapatnam.

India’s Coastal Vulnerability

India has a coastline of 7,516 km with 9 coastal states and 4 union territories
Over 170 million people live in India’s coastal districts
Sundarbans (West Bengal) — world’s largest mangrove delta; several islands already submerged; Lohachara Island was the first inhabited island to be submerged (2006)
Mumbai: Bandra-Kurla Complex, Nariman Point, and low-lying areas at risk
Chennai: Marina Beach area and northern coastal zones vulnerable
Kolkata: built on the Gangetic delta — highly vulnerable to flooding and sea level rise

🏔️ Glacial Retreat

Glaciers worldwide are retreating at accelerating rates due to rising temperatures
Himalayan glaciers — called the “Third Pole” — contain the largest concentration of ice outside the polar regions
Over 9,000 glaciers in the Himalayas; feed major rivers: Ganga, Indus, Brahmaputra, Yangtze, Mekong
Gangotri Glacier (source of Ganga) — retreating at ~22 metres per year; has retreated ~2 km since 1780
Siachen Glacier — world’s largest non-polar glacier; also retreating
Short-term effect: increased river flow (glacial melt adds water) → flooding
Long-term effect: glaciers disappear → rivers lose their dry-season flow → water scarcity for hundreds of millions

📌 GLOF (Glacial Lake Outburst Flood): As glaciers melt, they form glacial lakes dammed by ice or moraine. When these dams fail, catastrophic floods occur downstream. India has experienced several GLOFs — the 2021 Chamoli disaster (Uttarakhand) was linked to a glacial lake outburst, killing 200+ people. GLOFs are increasing with climate change.

🌪️ Extreme Weather Events

Climate change is making extreme weather events more frequent, more intense, and longer-lasting.

Event Type	Climate Change Link	India Examples
Cyclones	Warmer oceans provide more energy; rapid intensification more common; slower movement = more rainfall	Cyclone Amphan (2020), Cyclone Biparjoy (2023), increasing Bay of Bengal cyclone intensity
Floods	Warmer atmosphere holds more moisture (7% more per 1°C) → heavier rainfall events	Kerala floods (2018, 2019), Uttarakhand floods (2013, 2021), Chennai floods (2015)
Droughts	Altered precipitation patterns; increased evaporation; shifting monsoon	Maharashtra drought (2018–19), Bundelkhand chronic drought
Heatwaves	Baseline temperatures higher; heat extremes more frequent and intense	India heatwaves (2022, 2023) — temperatures exceeding 45°C in Rajasthan, UP, Delhi
Wildfires	Hotter, drier conditions; longer fire seasons	Uttarakhand forest fires (increasing frequency)
Cold waves	Arctic warming disrupts polar vortex → cold air spills south	North India cold waves; paradoxically linked to Arctic warming

⭐ Attribution Science: Scientists can now calculate how much more likely a specific extreme event was due to climate change. For example, the 2022 Pakistan floods were made 50% more likely by climate change. The 2021 North American heat dome was “virtually impossible” without climate change. This field is called extreme event attribution.

🪸 Coral Bleaching

Corals live in a symbiotic relationship with zooxanthellae (photosynthetic algae) that live in their tissues and provide 90% of their energy
When water temperature rises by just 1–2°C above the summer maximum for several weeks, corals expel their zooxanthellae → corals turn white (bleaching)
Bleached corals are stressed but not dead — if temperatures return to normal quickly, they can recover
Prolonged bleaching → coral death → loss of entire reef ecosystem
Great Barrier Reef (Australia) — world’s largest coral reef; experienced mass bleaching in 1998, 2002, 2016, 2017, 2020, 2022 — most severe bleaching on record in 2022
India’s coral reefs: Lakshadweep Islands, Andaman & Nicobar Islands, Gulf of Mannar, Gulf of Kutch — all experiencing bleaching events
Lakshadweep experienced severe bleaching in 1998 and 2010; over 90% bleaching in some areas

📌 Ocean Warming + Acidification Double Threat: Corals face a double threat — warming causes bleaching, while ocean acidification (see below) weakens their calcium carbonate skeletons. Together, these make coral survival increasingly difficult. Coral reefs support ~25% of all marine species despite covering less than 1% of the ocean floor.

🧪 Ocean Acidification

Oceans absorb approximately 25–30% of human CO₂ emissions each year
CO₂ dissolves in seawater → forms carbonic acid (H₂CO₃) → dissociates → releases hydrogen ions → pH drops
Ocean pH has dropped from 8.2 (pre-industrial) to 8.1 (current) — a 26% increase in acidity (pH is logarithmic)
Projected to reach 7.95 by 2100 under high-emission scenarios
Effects:
- Harms calcifying organisms — corals, oysters, mussels, sea urchins, pteropods (sea butterflies) — their shells dissolve in acidic water
- Disrupts fish behaviour and sensory systems
- Reduces ocean’s ability to absorb more CO₂ (positive feedback)
- Threatens the entire marine food web

⭐ Exam Fact: Ocean acidification is sometimes called the “other CO₂ problem” or “evil twin of climate change.” The current rate of ocean acidification is the fastest in at least 300 million years. Pteropods (tiny sea snails) are called the “canary in the coal mine” for ocean acidification — their shells are already dissolving in parts of the Southern Ocean.

🦋 Species Extinction & Biodiversity Loss

Habitat loss — rising temperatures make habitats unsuitable; species must migrate or face extinction
Range shifts — species moving poleward or to higher altitudes; some have nowhere to go (mountain-top species)
Phenological mismatch — timing of biological events (flowering, migration, breeding) shifts; predator-prey and pollinator-plant relationships disrupted
Coral reef loss — 25% of marine species depend on reefs; reef loss = mass marine extinction
Polar species — polar bears, Arctic foxes, penguins threatened by sea ice loss
IPCC AR6: climate change is a major driver of biodiversity loss; at 1.5°C, 4–8% of species face high extinction risk; at 3°C, 29% of species at risk
India: Snow leopard, Himalayan brown bear, one-horned rhinoceros (flooding), Irrawaddy dolphin, Olive Ridley turtles (nesting beach loss) all threatened

🌾 Food Security

Climate change threatens food production through multiple pathways
Crop yield changes: wheat and maize yields declining in many regions; rice yields affected by heat stress during flowering
Shifting agricultural zones: some regions become unsuitable; new areas may open up (e.g., higher latitudes)
Water stress: changing rainfall patterns and glacier retreat reduce irrigation water availability
Extreme events: floods, droughts, and heatwaves destroy crops
CO₂ fertilisation effect: higher CO₂ can boost some crop yields (wheat, rice) but reduces nutritional quality (lower protein, zinc, iron)
IPCC: global crop yields could decline by 2–6% per decade while food demand increases by 50% by 2050

📌 India & Food Security: India is highly vulnerable — agriculture employs ~45% of the workforce and contributes ~17% of GDP. Studies project wheat yields in India could fall by 6–25% by 2100. Rice yields in eastern India could decline. The Indo-Gangetic Plain — India’s breadbasket — faces increasing heat stress and water scarcity.

🇮🇳 India-Specific Impacts of Climate Change

Impact Area	Details
Monsoon Variability	Indian monsoon becoming more erratic — longer dry spells interspersed with intense rainfall events; overall monsoon rainfall may increase but become more unpredictable; El Niño years bring drought
Himalayan Glacier Retreat	Threatens long-term water security for 500+ million people dependent on Himalayan rivers; increased GLOF risk; Gangotri retreating ~22 m/year
Coastal Flooding	Mumbai, Chennai, Kolkata, Kochi at risk; Sundarbans islands submerging; 170 million coastal residents vulnerable
Heat Stress	India among most heat-stressed countries; 2022 heatwave caused crop failures and health emergencies; wet-bulb temperature approaching human survivability limits in some areas
Agricultural Disruption	Wheat and rice yields declining; shifting crop zones; water stress in Punjab and Haryana (groundwater depletion + reduced glacier melt)
Coral Reef Damage	Lakshadweep and Andaman reefs bleaching; threat to fisheries and tourism
Cyclone Intensification	Bay of Bengal cyclones intensifying rapidly; Arabian Sea cyclone frequency increasing (unusual)
Biodiversity Loss	Western Ghats, Eastern Himalayas (biodiversity hotspots) under threat; snow leopard, one-horned rhino, Olive Ridley turtles at risk

⭐ Wet-Bulb Temperature: A measure combining heat and humidity. At a wet-bulb temperature of 35°C, the human body cannot cool itself through sweating — survival is impossible beyond 6 hours even for healthy adults in shade. Parts of India, Pakistan, and the Persian Gulf are already approaching this threshold during extreme heat events.

✅ Revision Checklist — Effects of Climate Change

✅ Sea level rise = thermal expansion (~50%) + glacial/ice sheet melt
✅ Current sea level rise rate = ~3.3–3.7 mm/year (accelerating)
✅ Most at risk: Maldives (avg 1.5 m elevation), Tuvalu, Bangladesh, Kiribati
✅ Lohachara Island (Sundarbans) = first inhabited island submerged (2006)
✅ Himalayan glaciers = “Third Pole” = 9,000+ glaciers = feed Ganga, Indus, Brahmaputra
✅ Gangotri Glacier = source of Ganga = retreating ~22 m/year
✅ GLOF = Glacial Lake Outburst Flood = increasing with climate change
✅ Warmer atmosphere holds 7% more moisture per 1°C → heavier rainfall
✅ Coral bleaching = water temp rises 1–2°C → corals expel zooxanthellae → turn white
✅ India’s coral reefs = Lakshadweep, Andaman & Nicobar, Gulf of Mannar, Gulf of Kutch
✅ Ocean acidification = CO₂ + seawater → carbonic acid → pH drops
✅ Ocean pH = 8.2 (pre-industrial) → 8.1 (current) = 26% more acidic
✅ Harms calcifying organisms = corals, oysters, pteropods
✅ Phenological mismatch = timing of biological events disrupted
✅ CO₂ fertilisation = boosts some yields but reduces nutritional quality
✅ India: monsoon variability + glacier retreat + coastal flooding + heat stress
✅ Wet-bulb 35°C = human survival limit = parts of India approaching this
✅ India’s coastal population = 170 million people at risk