1
Increased Frequency & Severity of Heatwaves
2024 was the hottest year ever recorded in India and globally
💡 Think of Heatwaves Like a Pressure Cooker Without a Release Valve
A heatwave forms when a high-pressure system traps warm air over a region — like a lid on a pressure cooker. The trapped air can’t rise, clouds can’t form, rain can’t fall, and temperatures build day after day. Global warming is making these “lids” stay longer, press harder, and appear in places never seen before. India is uniquely vulnerable: it’s a tropical country, highly dependent on outdoor labour, and 75% of its workforce is exposed to heat at work.
IMD Definition — What Is a Heatwave?
IMD Heatwave Criteria (Know This for Prelims)
- Plains: Maximum temperature ≥ 40°C AND departure from normal ≥ 4.5°C → Heatwave | ≥ 6.5°C → Severe Heatwave
- Coastal stations: Maximum temperature ≥ 37°C with departure criteria same as plains
- Hilly areas: Maximum temperature ≥ 30°C with departure criteria
- Night heatwave (new category): Minimum temperature 4–6.4°C above average = “warm night” | >6.4°C above = “severe warm night” — used in forecasts for first time in 2024
- Declared when conditions persist for at least 2 days over a meteorological subdivision
India Heatwave 2024 — The Worst on Record Current Affairs
733
Deaths across 17 states (HeatWatch) vs 459 official IMD figure — true toll undercounted
37 cities
Exceeded 45°C between March–June 2024 — unprecedented spatial extent
35.2°C
Delhi’s warmest night ever (minimum temperature) — 4–7°C above normal
🔴 India Heatwave 2024 — Key Facts for UPSC
- 2024 was the hottest year ever recorded in India and globally. Temperature was above normal in all months except March (IMD 2025)
- 37 cities exceeded 45°C between March–June 2024. Churu (Rajasthan) and Phalodi briefly touched 50°C.
- 40,000+ heatstroke cases reported across India. Deaths: 459 (official IMD) vs 733 deaths across 17 states (HeatWatch) — discrepancy due to poor data collection, lack of awareness among healthcare workers
- Delhi’s warmest night: 35.2°C minimum temperature — a record. 24 nights in May–June with temperature above 30°C — double the average for 2001–2010
- Nighttime warming faster than daytime: IMD confirmed dangerous trend — warm nights increase heat stress as bodies can’t recover. Alwar, Rajasthan: 37°C minimum on June 18 — highest in 55 years
- Election duty deaths: 33 election workers died on heatstroke duty during Lok Sabha elections 2024 — held entirely during the heatwave season (March–June)
- Water crisis: Delhi faced severe water shortage — rivers parched, tankers deployed. Heatwave increased consumption while reducing river levels simultaneously
- 2025 onset: Heatwaves in India began in March 2025 — 20 days earlier than 2024. February 2025 was the warmest February since 1901.
Long-term Trends & India’s Vulnerability
Heatwave Trends — India Specific Data
- 57% of Indian districts are at high or very high risk from extreme heat (Prabhu et al., 2025)
- India is 15% more vulnerable to heat extremes than in 1990 (Lancet Countdown on Health and Climate Change)
- Heatwaves likely to last 25× longer by 2036–2065 if carbon emissions remain high (G20 International Climate Report)
- 34 million job losses projected due to heat stress by 2030 — mostly in agriculture, construction (World Bank, 2022)
- 75% of India’s workforce exposed to heat at work — among the highest globally
- 1 day of nationwide heatwave can cause ~3,400 deaths (Gadgil & Narang, 2025 estimate)
- Since 1990: one-quarter of global heat-wave-related excess deaths have occurred in India (Zhao et al., 2021)
- Most vulnerable states: Rajasthan, Punjab, Haryana, Delhi, UP, Madhya Pradesh, Chhattisgarh, Odisha, Vidarbha (Maharashtra), Gangetic West Bengal, coastal Andhra Pradesh, Telangana
Urban Heat Islands (UHI)
Urban Heat Islands — Definition and Causes
- Definition: Urban areas that are significantly warmer than surrounding rural areas due to human activities — concrete, asphalt, reduced vegetation, waste heat from vehicles/buildings/industry
- Mechanism: Dark surfaces (asphalt, concrete) absorb more solar radiation → store heat → release at night → cities don’t cool down as much as natural landscapes
- Magnitude: Urban areas can be 1–7°C warmer than surrounding rural areas. Night-time UHI stronger than daytime (cities release stored heat after sunset)
- Key drivers: Reduced vegetation (less evapotranspiration) | Impervious surfaces (no water infiltration) | Waste heat from ACs/vehicles/industries | Canyon effect — tall buildings trap heat | Dark materials with low albedo
- Delhi UHI: Average minimum temperature in May rose from 23.6°C (2001–2010) to 24.5°C (2020–2023) to 28°C in May 2024 — 2025 Delhi Heat Action Plan includes 3,000 water-coolers, shaded footpaths, “cool” roofs
- Solutions: Urban greening (parks, trees) | Cool roofs/pavements (white/light colours) | Green roofs | Heat corridors | Restricting dark surfaces | Urban planning with vegetation corridors
Heat Domes
Heat Dome — The Atmospheric Pressure Cooker
- Definition: A meteorological phenomenon where a high-pressure system traps an air mass, preventing it from rising and cooling — like a dome-shaped lid over a region
- Mechanism: High pressure forces warm air downward → suppresses convection → no cloud formation → no rainfall → temperatures build up day after day. Can persist for days to weeks.
- Global examples: Pacific Northwest (USA/Canada) 2021 — 49.6°C in Lytton, British Columbia, the highest temperature ever recorded in Canada. Europe 2019, 2022 heatwaves linked to heat domes. India 2022 and 2024 heatwaves — heat dome conditions over Northwest India
- Climate change link: A warming Arctic is weakening the jet stream → makes the jet stream more “wavy” and slow-moving → allows high-pressure systems (heat domes) to stall in place for longer periods instead of moving eastward
- Difference from heatwave: Heat dome is the atmospheric MECHANISM; heatwave is the OBSERVED SURFACE OUTCOME of the heat dome
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Marine Heat Waves (MHW)
Oceans absorb 90% of excess heat — when they overheat, cascading ecological catastrophe follows
Marine Heatwaves — Definition and Key Facts
- Definition: A prolonged period of anomalously high sea surface temperature (SST) — typically ≥5 days with SST exceeding the 90th percentile of historical climatology
- Global trend: Marine heatwaves have become more frequent, longer, and more intense since the 1980s due to ocean warming (oceans absorb 90%+ of excess heat trapped by GHGs)
- 2023–2024 North Atlantic: Unprecedented marine heatwave — North Atlantic SSTs shattered records by >1°C above previous records. Contributed to record global average temperatures in 2023 and 2024.
- Indian Ocean warming: The Indian Ocean is warming at a rate faster than most ocean basins — contributing to intensified cyclones, disrupted monsoon patterns, and coral bleaching. Arabian Sea SST has risen by 0.8°C since 1980.
- Impacts of MHWs:
- Coral bleaching: Mass bleaching events triggered by MHWs — 4th global coral bleaching event (2023–24) affected 54+ countries including India
- Species displacement: Fish, marine mammals move to cooler waters — disrupts fishing communities
- Harmful algal blooms: Warm, nutrient-rich conditions promote toxic algal blooms → “dead zones” in ocean
- Cyclone intensification: Warm SSTs are the fuel for tropical cyclones — MHWs enable rapid intensification
- Seagrass and kelp die-offs: Critical marine carbon sinks destroyed
- IPCC SROCC (2019): Marine heatwaves have doubled in frequency since 1982 and are projected to become 20× more frequent at 2°C of warming. 90% of extra heat from climate change has gone into the ocean.
3
Increased Incidence & Intensity of Wildfires
40% increase in forest fires in two decades · Fire season starts earlier, ends later
🔴 State of Wildfires 2024–25 Report (Copernicus/ECMWF) — Latest Current Affairs
- Period: March 2024 – February 2025
- Burned area: 3.7 million km² — 9% below long-term average. But this masks the real story:
- Carbon emissions: 2.2 Pg C (2.2 billion tonnes of carbon) — 9% ABOVE average, 6th highest since 2003. Equivalent to more than 8 billion tonnes of CO₂
- The Paradox: Less area burned BUT more carbon released — because fires burned in dense, carbon-rich forests (Amazon, Canadian boreal) rather than African savannahs (large area, low carbon). Location of fires matters more than total area.
- Worst fires 2024–25:
- Canada (Jasper, Alberta): Jasper wildfire destroyed one-third of the town’s structures — insured damages ~C$1.23 billion. Overall 2024 Canada fire season: 6th most destructive ever, 5.3 million hectares burned
- South America: Brazil, Bolivia — extreme drought (El Niño amplified) drove record emissions from Amazon and Cerrado dry forests
- Canada’s boreal forests: 2023-24 season had over 9× average carbon emissions from Canadian boreal (worst global record)
- 2025 fires: Spain, Portugal, Turkey, South Korea — analysis shows Spain/Portugal fires 40× more likely due to climate change (World Weather Attribution group)
Why Are Wildfires Getting Worse? — Climate Links
- 40% increase in extent of forest fires over past ~2 decades, predominantly in extratropics
- 2× increase in intensity of globally extreme fires over same period
- Longer fire seasons: Starting earlier in spring, ending later in autumn. Fire season extends by weeks globally due to warming-induced drought.
- Zombie fires (Arctic): Fires that smoulder underground through winter in peat and organic soil → reignite in spring without new ignition. Now occurring in boreal forests and even tundra — previously thought too cold for fires. Extremely dangerous as peat contains centuries of stored carbon.
- Drought-fire feedback: Warming → drought → dry vegetation (fuel) → fire → releases CO₂ → more warming. A vicious cycle.
- India wildfires: Central India (Madhya Pradesh, Chhattisgarh, Odisha) increasingly prone to wildfires due to heat-drought conditions. Uttarakhand forest fires have intensified in frequency and area. Lightning-started fires increasing as climate warms.
4
Shrinking Cryosphere — Glaciers, Ice Sheets & Permafrost
The world’s glaciers lost 6.5 trillion tonnes of ice in just 23 years (2000–2023)
💡 The Cryosphere Is Earth’s Air Conditioner — And We’re Switching It Off
The cryosphere (from Greek: “kryos” = cold) refers to all frozen water on Earth: glaciers, ice caps, ice sheets (Greenland, Antarctica), sea ice, permafrost, and seasonal snow cover. This frozen world regulates Earth’s temperature through the albedo effect — white ice reflects sunlight back to space, cooling the planet. As ice melts, dark ocean/land is exposed → absorbs more heat → accelerates melting. This is a classic positive feedback loop that is already operating in the Arctic and Himalayas.
🔴 Glambie Study 2024 (Nature) — Global Glacier Data
- Source: Glacier Mass Balance Intercomparison Exercise (GLAMBIE) — combines satellite laser altimetry, radar, optical, and field measurement data
- Published in: Nature journal, 2024
- Key finding: World’s glaciers collectively lost 6.542 trillion tonnes of ice between 2000 and 2023
- Sea level contribution: This caused an 18 mm (0.7 inch) rise in global sea levels — from glacier melt alone (on top of thermal expansion)
- Annual rate: Glaciers losing 273 billion tonnes of ice per year
- Regional variation: Since 2000, glaciers have lost 2%–39% of their ice regionally (and ~5% globally)
India & Himalayan Cryosphere — Critical Data
- WMO State of Climate in Asia 2024: 23 of 24 glaciers in the Central Himalayas are losing mass — accelerating flood risk from Glacial Lake Outburst Floods (GLOFs)
- Nepal glaciers: Lost significant mass in 2024, threatening hydropower stations, roads, and mountain communities
- Himalayan temperatures: Mean temperature of the Himalayas has risen by 0.6°C in the past 30 years — frequency of warmer days increasing
- GLOF threat: As glaciers melt, they leave behind glacial lakes. These can burst suddenly, sending catastrophic flood waves downstream. The Sikkim GLOF (October 2023) killed 40+ and destroyed the Teesta hydropower project — most notable recent example.
- Himalayan rivers at risk: Ganga, Indus, and Brahmaputra depend on glacier melt for summer flow. As glaciers shrink, initial flooding phase followed by reduced flow — “peak water” crisis threatening drinking water, agriculture, and hydropower for hundreds of millions
- Third Pole: Himalayas contain the world’s largest store of ice outside the polar regions — called the “Third Pole.” Home to ~54,000 glaciers. Melting faster than Arctic in terms of percentage. India, Pakistan, China, Nepal, Bhutan all face downstream impacts.
- Permafrost thaw: Arctic permafrost thawing releases methane (CH₄) — a greenhouse gas 80× more potent than CO₂ over 20 years. This is a major tipping point risk. Permafrost also destabilises infrastructure, causing building collapse and road damage in Arctic regions.
New Arctic Sea Routes — A Double-Edged Impact
Arctic Sea Ice Decline — Strategic & Environmental Implications
- Arctic sea ice loss: Arctic sea ice extent is declining at ~13% per decade (NSIDC). Summer Arctic could be ice-free by 2040–2050 under high emission scenarios.
- Northern Sea Route (NSR): As Arctic ice melts, the northern passage along Russia’s Arctic coast becomes navigable — cutting shipping distance between Asia and Europe by ~40% vs Suez Canal route
- Northwest Passage: Through Canadian Arctic — also increasingly navigable
- Strategic significance for India: Shorter route for India’s trade with Europe/North America. India has observer status in the Arctic Council (since 2013) and has a research station — Himadri — in Svalbard (Norway). India’s Arctic Policy released in 2022.
- Risks: New shipping routes → more pollution in fragile Arctic ecosystem | Increased resource extraction (oil, gas, minerals) | Geopolitical competition (Russia claims extended Arctic shelf)
5
Sea Level Rise (SLR) — A Slow-Motion Catastrophe
Every cm of SLR exposes another 2 million people to annual flooding somewhere on our planet
Two Causes of Sea Level Rise
🌊
Thermal Expansion
~50% of SLR
As oceans warm, water molecules move faster and take up more space (thermal expansion). Oceans absorb 90% of excess heat from GHGs. In the Indian Ocean — expansion contribution is particularly high as the Indian Ocean is warming rapidly. Can’t be reversed quickly.
🧊
Ice Melt
~50% of SLR
Melting of: (1) Mountain glaciers (contributes 18mm rise 2000-2023 per GLAMBIE study). (2) Greenland Ice Sheet — melting faster, losing 280 bn tonnes/year. (3) Antarctic Ice Sheet — contains enough ice to raise SL by 58m if all melted. Ice loss → adds water to oceans → permanent sea level rise.
🔴 Global and India Sea Level Rise — Latest Data
- Global SLR rate (2013–2022): 4.5 mm per year — the fastest rate in the historical record (WMO). This is double the rate of the 1990s.
- Total SLR since 1901: Global mean sea level has risen 0.20 m (20 cm) between 1901 and 2018 (IPCC AR6)
- India’s coastline at risk: Arabian Sea rising at 3.9 ± 0.4 mm/year | Bay of Bengal rising at 4.0 ± 0.4 mm/year — BOTH surpassing global average of 3.4 mm/year (WMO State of Climate in Asia 2024)
- Ministry of Earth Sciences: Average sea level along Indian coast rose at ~1.7 mm/year during 1900–2000. Rate has accelerated since.
- India’s most affected cities (CSTEP 2024 report):
- Mumbai: Largest SLR — 4.44 cm rise between 1987 and 2021. Average elevation ~10m — highly vulnerable
- Kolkata: Located in Ganga delta — subsidence + SLR combined risk
- Chennai: Low-lying coastal city; frequent flooding already
- India’s coastline erosion: 32% of India’s coastline underwent sea erosion between 1990 and 2018 (National Centre for Coastal Research — NCCR)
- Low-lying regions: Regions within 50 km of India’s coast face increasing submergence risk (WMO Asia 2024)
- WMO report: India, China, Bangladesh, and the Netherlands face the highest threat of sea-level rise globally
- A 3 cm SLR = sea intrudes 17 metres inland. At 5 cm/decade rate = 300 metres of coastline lost per century.
- Glambie 2024 (Nature): Glacier melt alone caused 18 mm of sea level rise 2000–2023
Vulnerable Areas in India
India’s Most Vulnerable Areas to SLR
- Sundarbans (West Bengal): World’s largest mangrove delta. Already experiencing island submergence — Sagar Island, Ghoramara. ~4.5 million people at risk. Sea level rising faster than mangroves can migrate.
- Lakshadweep: Average elevation <2m. A study projected significant airport and residential area flooding due to SLR. India's smallest UT at existential risk.
- Coastal Andhra Pradesh & Odisha: Low-lying Krishna-Godavari delta and Mahanadi delta highly vulnerable. Combined with cyclone risk = compounding threat.
- Mumbai: Sea level rising fastest among Indian cities (4.44 cm in 34 years). Already faces flooding during monsoon + high tide combination (known as “king tide flooding”).
- Kerala coast: Kerala has lost significant land area to erosion over past decades. Coastal communities fishing villages are being displaced.
Small Island Developing States (SIDS) — Existential Crisis
SIDS — The Nations Drowning for Others’ Sins
- Tuvalu: Pacific island nation — average elevation 2m. Plans to create digital “nation in cloud” to preserve statehood even after physical territory is submerged. First nation pursuing legal nationhood without territory. In November 2023, signed Falepili Union with Australia for climate mobility.
- Maldives: Average elevation 1.2m — 80% of territory less than 1m above sea level. Capital Malé already protected by sea wall. Plans for floating city in Hulhumalé lagoon. Has become the loudest voice for 1.5°C limit.
- Kiribati: Pacific island nation — has pre-emptively bought land in Fiji for potential population relocation. Already experiencing saltwater intrusion into freshwater lenses.
- Panama — Gardi Sugdub: ~300 families recently relocated from Guna Yala island due to rising seas — one of the first climate relocations of an entire community in the Americas.
- Jakarta, Indonesia: Capital being relocated to Borneo (Nusantara) — due to combination of sea level rise AND land subsidence from over-extraction of groundwater. Jakarta sinking by 25cm/year in some areas.
- SIDS in climate negotiations: SIDS push hardest for 1.5°C limit (vs 2°C) — the difference between survival and submergence. AOSIS (Alliance of Small Island States) is their unified negotiating bloc in UNFCCC.
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Tropical Cyclones — Fewer But More Violent
Warming oceans = more fuel for storms · Arabian Sea cyclones now a new normal
How Climate Change Is Transforming Cyclones
- Core mechanism: Warm sea surface temperatures (SSTs) fuel cyclones. As oceans warm → more energy available → cyclones intensify more rapidly and reach higher peak intensities
- Bay of Bengal warming: 0.20°C per decade since 1982 (MoES, 2024) — directly increasing cyclone intensity and duration. Bay of Bengal is now anomalously warm relative to historical averages.
- Arabian Sea warming: 0.8°C rise since 1980 — historically the Arabian Sea was too dry, too windy (high wind shear) for cyclones. Warming is changing this — more frequent and intense Arabian Sea cyclones.
- Rapid intensification (RI): WMO (2024) reports 25% of Indian Ocean cyclones now show “rapid intensification” — double the rate from the 1980s. RI = wind speed increases ≥55 km/h in 24 hours. Dangerous because it gives coastal populations little warning.
- Cyclone Mocha (2023): Reached sustained winds of 215 km/h — the strongest cyclone in the Bay of Bengal in 16 years. Made landfall near Cox’s Bazar/Sittwe (Bangladesh/Myanmar). Anomalously warm SSTs were the key driver.
- Cyclone Asna (2024): Unusual — formed as a land-based depression in Rajasthan, moved through Gujarat, then intensified upon reaching the Arabian Sea. First such inland-origin Arabian Sea cyclone in recorded history — linked to extreme monsoon + SST anomaly.
- Seasonality shifting: Cyclones now occurring beyond traditional seasons (Oct–Dec). Pre-monsoon cyclones (April–May) in Bay of Bengal and Arabian Sea becoming more frequent.
- Rainfall intensification: Warmer air holds more moisture (Clausius-Clapeyron relation: ~7% more moisture per 1°C warming) → cyclones carry more rainfall → greater flood risk even after landfall
- Northward track shift: Cyclone tracks in the Arabian Sea are shifting northward — threatening Gujarat, Maharashtra, and even Pakistan’s Makran coast (historically less cyclone-prone)
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Deterioration of Carbon Sinks
The natural buffers that absorb our CO₂ are weakening — the climate safety net is fraying
Carbon Sinks — What Are They and Why Are They Failing?
- Carbon sink: Any system that absorbs more carbon from the atmosphere than it releases. Major natural sinks: Oceans (~26% of human CO₂), Forests/land (~30% of human CO₂). The remaining ~44% stays in atmosphere causing warming.
- Tropical rainforests turning to sources: Some parts of the Amazon are now emitting more CO₂ than they absorb due to deforestation + drought + fire. UPSC 2025 editorial topic: “Tropical Rainforests Turning from Carbon Sinks to Net Emitters.”
- Ocean carbon sinks weakening: As oceans warm, they absorb less CO₂ (warmer water holds less dissolved gas). Ocean warming + acidification → reduced biological carbon pump efficiency → less CO₂ absorbed
- Permafrost carbon bomb: Arctic permafrost stores ~1,500 billion tonnes of carbon (twice the amount currently in the atmosphere). As permafrost thaws, microbial decomposition releases this carbon as CO₂ and CH₄ — a massive positive feedback.
- CO₂ fertilisation (partial positive): Higher CO₂ levels in atmosphere can stimulate plant growth in some regions — a negative feedback that partially offsets warming. However, this effect is limited by water, nutrients, and temperature — and is overwhelmed by direct warming damage at higher temperatures.
- Wildfire impact on sinks: Wildfires convert forests from carbon sinks to carbon sources instantly. 2024–25 wildfires emitted 2.2 Pg C — that’s carbon that took decades to absorb, released in months.
- India’s sink target: India’s NDC includes creating an additional carbon sink of 2.5–3 billion tonnes CO₂ equivalent by 2030 through forest and tree cover. Green India Mission, Aravalli Green Wall Project are key mechanisms.
8
Other Impacts of Global Warming
Economic losses · Climate migrants · Ocean deoxygenation · Biodiversity · Food & Health security
💸
Economic Losses
$16 Mn/hr from climate disasters
Munich Re 2024: Climate-related disasters cost the world ~$260 billion in 2023 alone. India loses ~$87 billion annually to climate impacts. Heat stress causes $600 billion in productivity losses/year globally. Drought costs global economy $307 billion/year (UNCCD COP-16).
🧑🤝🧑
Climate Migrants
216 Mn internal migrants by 2050
World Bank: 216 million people could be internal climate migrants by 2050 — driven by sea level rise, drought, extreme heat. South Asia most affected (40 million). India’s coastal populations, Sundarbans residents, and drought-affected farmers are already moving. Kiribati, Tuvalu buying land for relocation.
🐟
Ocean Deoxygenation
Dead zones expanding globally
Warmer water holds less dissolved oxygen. Stratification of oceans (warm surface/cold deep) prevents mixing → oxygen depletion in deeper layers → “dead zones” expand. Arabian Sea has a large natural “oxygen minimum zone” that is expanding. Affects fish populations, fisheries, marine ecosystems. WHO calls it “ocean suffocation.”
🐘
Biodiversity Loss
~1 million species threatened
IPCC: At 1.5°C warming, 4% of species face very high extinction risk; at 2°C, 18%; at 3°C, 29%. Coral reefs — support 25% of marine biodiversity — at risk of complete collapse at 2°C. Polar species (polar bear, Arctic fox) face habitat loss. Phenological mismatch: species shifting timing out of sync with each other.
🌾
Food & Health Security
250,000 additional deaths/year by 2030
WHO projects ~250,000 additional deaths/year by 2030 from malnutrition, malaria, diarrhoea, and heat stress due to climate change. At 2°C warming → crop production reduced 12% in India → more imports needed. India’s agriculture 60%+ rain-dependent → climate variability = food insecurity. Vector-borne diseases (malaria, dengue, chikungunya) expanding range into new altitude zones as temperatures rise.
Ocean Acidification — The Other CO₂ Crisis
Ocean Acidification — CO₂ Dissolving in Seawater
- Mechanism: Oceans absorb ~26% of CO₂ emitted. CO₂ + H₂O → H₂CO₃ (carbonic acid) → lowers ocean pH
- Scale of change: Ocean pH has dropped from 8.2 (pre-industrial) to 8.1 today — seemingly small, but represents a 26% increase in acidity (pH is logarithmic)
- Record 2024: Atmospheric CO₂ reached 422.5 ppm in 2024 — about 50% higher than pre-industrial levels (IEA Global Energy Review 2025)
- Impact on marine life: Molluscs (clams, oysters, mussels) struggle to build calcium carbonate shells in acidic water | Coral reefs bleach AND become structurally weaker | Pteropods (sea butterflies) — base of marine food chain — shells dissolve | Plankton disrupted
- India: Lakshadweep, Gulf of Mannar, Gulf of Kutch, Andaman corals all under threat from combined warming + acidification
⭐ Complete Impact of Global Warming — Cheat Sheet
- Heatwave (IMD): Plains ≥40°C + departure ≥4.5°C | Coastal ≥37°C | Hills ≥30°C | Must persist ≥2 days
- India 2024 heatwave: 733 deaths (HeatWatch) | 40,000+ heatstroke cases | 37 cities >45°C | Delhi warmest night 35.2°C | 2025 onset 20 days earlier
- Long-term India heat trends: 57% districts at high/very high risk | 15% more vulnerable than 1990 | Heatwaves to last 25× longer by 2036-65 | 34 million job losses by 2030 | 75% workforce exposed to heat
- Urban Heat Islands: Cities 1-7°C warmer | Dark surfaces absorb heat | Night UHI > Day UHI | Delhi May avg min temp: 23.6°C (2001-10) → 28°C (May 2024)
- Heat Dome: High-pressure system traps air (like a lid) → no convection → temperatures build. Climate change weakens jet stream → heat domes stall longer
- Marine Heat Waves: SST ≥90th percentile for ≥5 days | Doubled in frequency since 1982 | 20× more frequent at 2°C (IPCC SROCC) | Fuel cyclones + bleach corals | Indian Ocean warming faster than most
- Wildfires 2024-25: 3.7 million km² burned (9% below avg) | 2.2 Pg C emitted (9% ABOVE avg, 6th highest) | Paradox: less area, more carbon (dense forests burned) | Canada Jasper: C$1.23 billion damage | Zombie fires now in boreal/tundra | Forest fires up 40% in 2 decades
- Cryosphere: Glaciers lost 6.542 trillion tonnes 2000-2023 → 18 mm SLR (GLAMBIE/Nature 2024) | 273 billion tonnes/year loss rate | 23/24 Central Himalayan glaciers losing mass | Sikkim GLOF Oct 2023 | Permafrost thaw → methane release → tipping point risk
- Arctic sea routes: Northern Sea Route opening | Arctic ice-free summers by 2040-50 | India: Arctic Policy 2022, observer in Arctic Council, Himadri station in Svalbard
- Sea Level Rise: Global rate 2013-22 = 4.5 mm/yr (fastest ever) | Total since 1901: 20 cm (IPCC AR6) | Every 1 cm SLR = 2 million more people in annual flood risk
- India SLR: Arabian Sea 3.9 mm/yr | Bay of Bengal 4.0 mm/yr (both above global 3.4 mm/yr) | Mumbai: 4.44 cm since 1987 | 32% coastline eroded 1990-2018 | WMO: India, China, Bangladesh, Netherlands most at risk
- SIDS crisis: Tuvalu — digital nation plan + Falepili Union with Australia | Maldives — floating city + 1.2m elevation | Kiribati — bought Fiji land | Jakarta — relocating capital to Borneo (Nusantara)
- Cyclones: Bay of Bengal warming 0.20°C/decade | Arabian Sea warming 0.8°C since 1980 | 25% Indian Ocean cyclones now show rapid intensification (double 1980s rate) | Cyclone Mocha 2023 = 215 km/h, strongest in 16 yrs | Cyclone Asna 2024 = unprecedented land-origin Arabian Sea cyclone | AOSIS = Small Island States negotiating bloc
- Carbon sinks: Oceans absorb 26% of CO₂ | Forests absorb 30% | Amazon turning from sink to source in some areas | Permafrost = 1,500 Bn tonnes carbon stored | Wildfires convert forests to sources instantly
- Ocean acidification: pH fell from 8.2 → 8.1 = 26% more acidic | CO₂ at 422.5 ppm in 2024 (50% above pre-industrial) | Threatens corals, molluscs, pteropods, plankton
- Other impacts: Climate migrants: 216 million internal by 2050 (World Bank) | Biodiversity: 1 million species threatened | Food: 12% crop reduction in India at 2°C | Health: 250,000 additional deaths/year by 2030 (WHO) | Ocean deoxygenation: Arabian Sea OMZ expanding
🧪 Practice MCQs
Q1. Which of the following statements about the WMO State of the Climate in Asia 2024 Report are CORRECT?
1. The Arabian Sea is rising at 3.9 mm/year — above the global average.
2. 23 of 24 Central Himalayan glaciers are gaining mass.
3. The Bay of Bengal is rising at 4.0 mm/year — above the global average.
4. Asia is heating at twice the global average rate.
✅ Answer: (c) — Statements 1, 3, and 4 are correct. Statement 2 is WRONG.
1 ✅: WMO State of the Climate in Asia 2024 confirmed the Arabian Sea is rising at 3.9 ± 0.4 mm/year — above the global average of 3.4 mm/year. 2 ❌ Wrong (Classic UPSC Trap): The statement reverses the finding. The WMO report found that 23 of 24 glaciers in the Central Himalayas are losing mass — not gaining. This is accelerating the risk of GLOFs (Glacial Lake Outburst Floods) threatening downstream communities, hydropower stations, and roads across Nepal, India, and Bhutan. 3 ✅: Bay of Bengal is rising at 4.0 ± 0.4 mm/year — also above the global average. Both Indian Ocean arms are rising faster than the global average, compounding coastal flooding risks for India, Bangladesh, Sri Lanka, and Myanmar. 4 ✅: The WMO confirmed Asia is warming at twice the global average rate — a consistent finding across multiple reports. This means weather extremes, heatwaves, floods, and glacial melting are all intensifying faster in Asia than anywhere else on Earth. 2024 was the second warmest year on record in Asia.
Q2. With reference to “rapid intensification” of tropical cyclones, consider the following:
1. It refers to wind speed increasing by at least 55 km/h within 24 hours.
2. WMO (2024) reported that 25% of Indian Ocean cyclones now show rapid intensification — double the rate from the 1980s.
3. Warmer sea surface temperatures are the primary driver.
4. Cyclone Mocha (2023) was an example, reaching 215 km/h winds — strongest in 16 years.
Select the CORRECT statements:
✅ Answer: (d) All four statements are correct
1 ✅: Rapid Intensification (RI) is defined as an increase in maximum sustained wind speed of ≥55 km/h (30 knots) within any 24-hour period. This is the internationally accepted meteorological definition. 2 ✅: WMO’s 2024 data shows that 25% of Indian Ocean cyclones now undergo rapid intensification — exactly double the rate observed in the 1980s. This is directly linked to the warming of the Bay of Bengal and Arabian Sea surface temperatures. 3 ✅: Warm sea surface temperatures (SSTs) provide the thermal energy and moisture that fuel tropical cyclones. As the Bay of Bengal warms by 0.20°C/decade and the Arabian Sea by 0.8°C since 1980, more energy is available for cyclogenesis and intensification. Rapid intensification requires not just warm surface water but also warm deep water — as intense storms stir up cooler water, if the warm layer is deep, intensification continues. 4 ✅: Cyclone Mocha (May 2023) reached peak sustained winds of 215 km/h — the strongest cyclone in the Bay of Bengal in 16 years. It was driven by anomalously warm Bay of Bengal SSTs and made catastrophic landfall near Cox’s Bazar (Bangladesh) and Sittwe (Myanmar), primarily affecting the world’s largest refugee camp.
Q3. The GLAMBIE (Glacier Mass Balance Intercomparison Exercise) study published in Nature (2024) found that:
a) World glaciers collectively lost 6.542 trillion tonnes of ice between 2000 and 2023
b) This caused 18 mm of global sea level rise
c) Glaciers are losing 273 billion tonnes of ice per year
d) Glaciers have lost between 2% and 39% of their ice regionally since 2000
Which combination is CORRECT?
✅ Answer: (d) All of a, b, c and d are correct
The GLAMBIE (Glacier Mass Balance Intercomparison Exercise) study — the most comprehensive global glacier assessment ever conducted — combined satellite laser altimetry, radar, optical imaging, and ground measurements to produce these findings: (a) 6.542 trillion tonnes: Total ice mass lost by ALL of Earth’s glaciers (excluding Greenland and Antarctic ice sheets) between 2000 and 2023. To put this in perspective: 1 trillion tonnes = 1 billion million tonnes. This is an unimaginable quantity of frozen freshwater permanently converted to ocean water. (b) 18 mm sea level rise: From glacier melt alone over 23 years. This is separate from the sea level rise caused by thermal expansion of warming oceans and by Greenland/Antarctic ice sheet melt. Combined SLR from all sources: ~20 cm since 1901 (IPCC AR6). (c) 273 billion tonnes/year: The current annual rate of glacier mass loss — meaning we’re still accelerating. At this rate, many smaller mountain glaciers (Alps, Andes, Rockies) could disappear within decades. (d) 2%-39% regionally: Shows the huge variation — some glacier regions (tropical glaciers in Andes/Africa) have lost nearly 40% of their ice; others less so. Globally about 5% of total glacier ice has been lost since 2000. This regional variation matters for UPSC as different regions face different water security timelines.
📜 UPSC Previous Year Questions (PYQs)
Consider the following statements:
1. In tropical regions, the onset of the wet season coincides with the onset of a warm phase of ENSO.
2. In India, heatwaves are more common in the post-monsoon season.
3. Areas in India that experience the risk of heat waves during summer months are in the north and northwest.
Select the correct answer:
✅ Official Answer: (c) 3 only
Statement 1 ❌ Wrong: ENSO’s warm phase (El Niño) is associated with SUPPRESSED rainfall in tropical regions including India. El Niño suppresses the Indian Summer Monsoon (ISM), causing below-normal rainfall. It does NOT coincide with the onset of wet season — in fact it often delays or weakens it. La Niña (cool phase) tends to enhance monsoon rainfall. Statement 2 ❌ Wrong: In India, heatwaves are most common in the pre-monsoon season — specifically March to June (May being the peak month). Post-monsoon season (October–December) is when cyclone season peaks, not heatwaves. The IMD issues maximum heatwave alerts in April, May, and early June before the monsoon breaks the heat. Statement 3 ✅: The regions most prone to heatwaves in India are indeed in the north and northwest — Punjab, Haryana, Delhi, Rajasthan, UP, and parts of Madhya Pradesh. These interior continental regions are furthest from the moderating influence of oceans, experience the “Loo” (a dry, hot westerly wind), have less pre-monsoon shower activity, and are the last to receive monsoon rains. Coastal areas and peninsular India are naturally cooler (sea breeze influence) and less prone to sustained heatwave conditions.
Consider the following statements:
1. The Global Ocean Observing System (GOOS) is an intergovernmental programme of UNESCO, IOC, WMO, UNEP, IAEA, and other bodies.
2. GOOS helps in the observations of sea level, ocean heat, salinity, and carbon.
3. The Indian Ocean Observing System (IndOOS) is the Indian component of GOOS.
Select the correct answer:
✅ Official Answer: (d) All three are correct
1 ✅: The Global Ocean Observing System (GOOS) is indeed an intergovernmental programme co-sponsored by UNESCO’s Intergovernmental Oceanographic Commission (IOC), WMO, UNEP, and other UN bodies. It coordinates a global network of ocean observations including buoys, floats, ships, and satellites. 2 ✅: GOOS specifically tracks: sea level (through tide gauges and satellite altimetry), ocean heat content (critical for understanding climate change), salinity (freshwater influx from ice melt changes ocean salinity and circulation), and ocean carbon (monitoring the ocean’s role as a carbon sink — increasingly important as oceans warm and absorb less CO₂). 3 ✅: IndOOS (Indian Ocean Observing System) is the Indian component of GOOS — a regional subset of the global observation network focused on the Indian Ocean. It maintains an array of moored buoys, Argo floats, and research vessels. This is directly relevant to monitoring the Arabian Sea and Bay of Bengal warming trends that are intensifying cyclones and sea level rise affecting India’s coasts.
❓ Frequently Asked Questions
These three are related but distinct concepts — and UPSC has tested all three. Think of it as three different levels of the same problem: Heat Dome (atmospheric cause): A heat dome is a meteorological event — a stationary high-pressure system that acts like a lid, trapping warm air over a region and preventing it from rising and cooling. Heat domes can persist for days to weeks and are the primary atmospheric MECHANISM behind extreme heatwaves. Climate change is making heat domes more persistent because a warming Arctic weakens the polar jet stream, causing it to meander more slowly and allowing high-pressure systems to stall. Heatwave (surface outcome): A heatwave is the OBSERVED CONSEQUENCE at the surface — prolonged period of excessively high temperatures. It’s what people experience. IMD defines it precisely (≥40°C + ≥4.5°C above normal for ≥2 days in plains). A heat dome typically triggers heatwaves, but not all heatwaves are caused by heat domes (some result from reduced pre-monsoon showers, Loo winds, etc.). Urban Heat Island (spatial modification): An Urban Heat Island is a chronic, permanent condition — cities are structurally warmer than surrounding rural areas due to built infrastructure (concrete, asphalt, reduced vegetation, waste heat). UHI doesn’t cause heatwaves but dramatically amplifies their impact — a heatwave that hits a city with a 4°C UHI effect is far deadlier than the same heatwave in a rural area. UHIs also mean cities don’t cool down at night as much, which is why nighttime temperature records are being broken in cities. In summary: Heat Dome → causes/intensifies → Heatwave → amplified in → Urban Heat Island areas.
Legacy IAS — UPSC Civil Services Coaching, Bangalore |
Sources: HeatWatch “Struck by Heat” report (September 2024) — 733 deaths; IMD 2025 — India heatwave 2024 data; Yale Climate Communication “Climate Change in Indian Mind, Spring 2025”; CBS News / Wikipedia — 2024 Indian Heat Wave; WMO State of the Climate in Asia 2024 (June 2025) — Arabian Sea 3.9 mm/yr, Bay of Bengal 4.0 mm/yr, 23/24 glaciers losing mass, Asia warming 2× global rate; GLAMBIE/Nature 2024 — 6.542 trillion tonnes ice lost, 18 mm SLR, 273 Bn tonnes/year; State of Wildfires 2024-25 (Copernicus/ECMWF, 2025) — 2.2 Pg C emissions, 3.7 million km² burned; Canada wildfire facts (Climate Institute Canada, June 2025); NCCR — 32% India coastline eroded; CSTEP Bengaluru 2024 — Mumbai 4.44 cm SLR; WMO “Global Sea-level Rise and Implications” — India, China, Bangladesh highest risk; Insights IAS — Cyclone Mocha 215 km/h; MoES 2024 — Bay of Bengal 0.20°C/decade warming; Insights IAS UPSC Synopsis October 2025 — 25% Indian Ocean cyclones rapid intensification, Arabian Sea 0.8°C rise since 1980.
