World Climate and Climate Change

Understanding the world's climate types provides the framework for answering questions on natural vegetation, agriculture, biodiversity, and human settlements. Why is sub-Saharan Africa dominated by savanna? Why does the Mediterranean region produce olives and wheat? Why is the Amazon so biodiversity-rich? Each climate type has a unique precipitation and temperature regime that explains the ecosystem and human activities associated with it.

Climate change — the overarching contemporary challenge — is also introduced in this chapter. UPSC has made climate change a near-annual Mains topic, requiring mastery of evidence, impacts, international frameworks, and India's position.

PART 1 — Quick Reference Tables

Table 1: Köppen's Climate Classification (Simplified)

Table 2: Climate Types and Vegetation

Table 3: Climate Change — Key Evidence

Table 4: IPCC and International Climate Agreements

Table 5: India and Climate Change

PART 2 — Detailed Notes

Köppen's Classification: The Standard System

Vladimir Köppen (1846–1940) developed the most widely used climate classification, based on temperature and precipitation values that correlate well with natural vegetation boundaries. He used letters to denote climate types:

• First letter: Major climate type (A, B, C, D, E)
• Second letter: Precipitation pattern (f = no dry season, s = dry summer, w = dry winter, W = desert, S = steppe)
• Third letter: Temperature (a = hot summer, b = warm summer, c = cool short summer, h = hot, k = cold)

India in Köppen's system:

• Af/Am: Kerala coast, Andaman & Nicobar, NE India
• Aw: Most of peninsular India (Deccan savanna climate)
• BWh: Thar Desert (Rajasthan, parts of Gujarat)
• Csa: Parts of Jammu, NW India (limited)
• Dfb/Dfc: Not in India mainland (possibly extreme Ladakh/Kashmir high zones)
• H (Highland): Himalayas, Western Ghats high zones

Major Climate Types: Detailed Notes

Tropical Rainforest (Af): Temperature consistently high (~27°C); heavy rainfall (>2,000 mm) distributed throughout the year; no distinct dry season. The stability of temperature and moisture supports the highest biodiversity on Earth — ~50% of all species in ~6% of land area. Amazon, Congo, Indonesian archipelago, parts of Kerala and the Andamans in India.

Tropical Savanna (Aw): Distinct dry season (3–6 months) with annual rainfall 750–1,500 mm concentrated in summer. The classic African savanna — grassland with scattered acacia trees — is this climate. In India, the Deccan Plateau has a savanna-like climate (dry winters, summer rains). Many of India's dry deciduous forests fall here.

Hot Desert (BWh): Annual rainfall <250 mm, often <50 mm. Extreme temperatures — very hot days (>45°C), cold nights (near 0°C in winter). Almost no vegetation. The Sahara, Arabian Desert, Atacama. India's Thar Desert (Rajasthan) receives ~150–300 mm, technically BSh (hot steppe) to BWh at its core.

Mediterranean (Csa/Csb): Unique pattern — wet, mild winters; hot, dry summers. Named for the Mediterranean basin but also found in California, Central Chile, SW Australia, South Africa's Cape. Drought-resistant, fire-adapted vegetation (maquis, chaparral, fynbos). The cradle of wheat and Mediterranean agriculture. The combination of wet winters and dry summers makes irrigation essential for summer crops.

Humid Subtropical (Cfa): Hot summers, mild winters, rain year-round. China, SE USA, SE Brazil, parts of South Asia. India's eastern coastal plains (Andhra–Odisha) approach this.

Marine West Coast (Cfb): The classic "British climate" — mild temperatures all year, perpetual overcast skies and moderate rain due to onshore westerlies over warm ocean currents. NW Europe, Pacific NW USA/Canada, SW New Zealand. No corresponding region in India.

Continental (Dfa/Dfb): Large temperature ranges (hot summers, very cold winters), moderate rainfall. Wheat and corn (maize) belts of North America and Central Europe. No equivalent in India (tropics prevent D climates except at high altitude).

Taiga (Dfc): Subarctic — very cold winters, short cool summers. Dominated by vast coniferous forests (Siberia's taiga = world's largest biome by area). Russia, Canada, Alaska. Podzol soils (acidic, low in nutrients).

Tundra (ET): Warmest month 0–10°C; permafrost (permanently frozen subsoil). Very short growing season. Mosses, lichens, dwarf shrubs. Arctic coasts of Russia, Canada, Alaska.

💡 Explainer: Climate Change — Mechanisms and Impacts

Enhanced greenhouse effect (see Chapter 8) raises global average temperature. Key cascading impacts:

Sea level rise (two components):

1. Thermal expansion: Warmer water expands in volume
2. Ice melt: Glaciers, ice sheets (Greenland, Antarctica) melt → freshwater added to ocean

Impact on India: 7,500 km coastline; 3 million people in cities at <10 m elevation; Mumbai, Chennai, Kolkata, Surat among vulnerable cities. Island territories (Lakshadweep, Andaman) face existence threat.

Himalayan glaciers and water security: India has ~10,000 glaciers in the Himalayas covering ~70,000 km². These glaciers are the "water towers of Asia" — they regulate river flow for hundreds of millions. Climate change is accelerating retreat. Short-term: more glacial lake outburst floods (GLOFs), flooding. Long-term: reduced dry-season river flow → water scarcity.

Agriculture impacts:

• Changed precipitation patterns → shifting monsoon reliability
• Higher CO₂ can initially boost some crops ("CO₂ fertilisation effect") but heat stress, drought, and flooding reduce yields overall
• IPCC estimates South Asian wheat yields could fall 15–25% by 2080 under high emissions scenarios

Ocean acidification: Oceans absorb ~25–30% of anthropogenic CO₂. CO₂ dissolves in seawater → carbonic acid → lowers pH. This threatens coral reefs (calcium carbonate skeletons dissolve), molluscs, and marine food chains. India's coral reefs (Gulf of Mannar, Gulf of Kutch, Lakshadweep, Andaman) are highly vulnerable.

🎯 UPSC Connect: Paris Agreement and India's Commitments

The Paris Agreement (adopted December 2015, COP21) is the most comprehensive climate framework:

• Long-term goal: Hold warming to well below 2°C above pre-industrial levels; pursue efforts to limit to 1.5°C
• NDCs: All countries submit their own targets; reviewed and updated every 5 years
• Finance: Developed countries to provide US$100 billion/year to developing countries for climate action (this target has been repeatedly missed)
• Loss and damage: Formally recognised at COP27 (Sharm el-Sheikh, 2022); fund established at COP28 (Dubai, 2023)

India's NDC (2022 update):

• Reduce emissions intensity of GDP by 45% from 2005 levels by 2030
• Achieve 50% of cumulative installed electric power capacity from non-fossil sources by 2030
• Create additional carbon sink of 2.5–3 billion tCO₂e through forest cover

India argues for equity in climate negotiations: developed countries are historically responsible for most cumulative emissions; India's per-capita emissions are far below global average; India needs space to develop.

PART 3 — Frameworks & Analysis

Climate Type Distribution Pattern

Climate Change: Global vs India Impacts

Exam Strategy

Prelims Traps:

• Mediterranean climate: Wet winters, dry summers — the reverse of monsoon pattern. California, Mediterranean basin, SW Australia, S. Africa, Chile.
• Taiga = coniferous (boreal) forest; Tundra = treeless with permafrost — do not confuse.
• Paris Agreement is NOT legally binding on individual country targets (NDCs are nationally determined) — but the overall framework and review process is legally binding.
• The IPCC does NOT do original research — it assesses and synthesises existing scientific literature.
• CBDR-RC (Common But Differentiated Responsibilities and Respective Capabilities) — the key equity principle in climate negotiations.

Mains Frameworks:

• Climate change impacts on India: use 5 dimensions — agriculture, water (glaciers), coastal, health, biodiversity.
• International climate negotiations: UNFCCC → Kyoto → Paris (progression) + India's equity argument.
• For "vulnerability of India to climate change" — use regional specificity (NE for floods, Rajasthan for drought, coasts for sea level rise, mountains for glaciers).

Previous Year Questions

1. UPSC Prelims 2021: Which of the following countries are vulnerable to the impacts of sea level rise? (Tests knowledge of low-lying coastal nations)
2. UPSC Prelims 2020: The Mediterranean climate is characterised by which of the following? (Wet winters, dry summers — tests climate type knowledge)
3. UPSC Mains GS3 2021: Discuss the impact of climate change on agricultural productivity in India and the adaptive strategies required.
4. UPSC Mains GS3 2022: Explain India's stance at international climate negotiations with reference to equity and common but differentiated responsibilities.