Climate Change — Comprehensive Study Guide

ECO 39556 | Hussen Ch. 9 | Prof. Chatterjee Lecture 15 | Sample-exam grounded

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1. Defining Climate Change

1.1 Two Definitions (Exam-Critical Distinction)

IPCC: Any change in climate over time due to natural variability OR human activity — the broader scientific definition. Hussen p. 206 uses this framing.

UNFCCC: Climate change attributed specifically to human activity — the narrower policy definition. The sample exam Q1 quotes this as "average change in global temperature and precipitation due to human economic activity."

The prof's juxtaposition of the two is a key conceptual point — scientists need the broader definition to study all climate variation; policymakers need the narrower one to assign responsibility for action.

1.2 The Greenhouse Effect Mechanism (Hussen pp. 206-208)

1. Solar shortwave radiation passes through the atmosphere to Earth's surface.
2. Earth's surface absorbs and re-emits the energy as infrared (longwave) radiation.
3. GHGs in the troposphere (CO₂, CH₄, N₂O, O₃, CFCs) absorb the outgoing IR.
4. GHGs re-radiate the trapped energy in all directions, including back toward Earth.
5. Net result: Earth's surface temperature is ~33°C warmer than without GHGs.

Without GHGs: Earth's surface would average −18°C instead of +15°C — life as we know it would be impossible.

1.3 Why CO₂ Dominates Despite Being the Weakest GHG Per Molecule

CO₂ dominates anthropogenic warming because of: (1) overwhelming abundance, (2) very long atmospheric residence time (decades to centuries), and (3) ongoing emissions from every economic sector.

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2. Evidence of Climate Change

2.1 The IPCC Institution

• Established 1988 by WMO + UNEP
• 195 member countries
• Role: assesses peer-reviewed science — does NOT conduct research
• Publishes Assessment Reports every 5-7 years (AR5: 2013-14, AR6 cycle 2021-23)
• Special Reports (e.g., SR1.5, 2018) appear between full ARs
• AR5: 95% confidence ("extremely likely") that human activity is the dominant cause of mid-20th-century warming

2.2 IPCC High-Confidence Findings

2.3 The Keeling Curve and CO₂ Evidence (Hussen p. 208)

Pre-industrial: ice cores show CO₂ stable at 260-280 ppm for ~10,000 years.

Mauna Loa Observatory: continuous CO₂ measurement since 1958 by Charles D. Keeling (Scripps):

• 1958: 310 ppm
• December 2017: 406.93 ppm
• 2024: 420+ ppm

The rate of rise itself is accelerating. Conversion: tons of carbon × 3.67 = tons of CO₂ (slide-only — not in Hussen).

2021 emissions: ~36.3 Gt CO₂ (fossil fuels) + ~4.5 Gt CO₂eq (other GHGs) = ~40.8 Gt CO₂eq total.

2.4 Climate Tipping Points (Hussen pp. 215-216)

A tipping point is a system threshold beyond which a small additional change triggers drastic, usually irreversible state changes. Examples:

• West Antarctic Ice Sheet collapse
• Amazon dieback
• Permafrost methane release
• AMOC (Atlantic circulation) disruption

Economic implication: tipping points make the damage cost function discontinuous, breaking the smooth MDC = MCC optimization. This is the strongest argument for precautionary mitigation beyond what a Nordhaus-style cost-benefit optimum would suggest.

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3. Economics of Climate Change

3.1 The MDC/MCC Framework

Tipping points create damage discontinuities that break this framework.

3.2 Stern vs. Nordhaus

The disagreement is fundamentally about INTER-GENERATIONAL ETHICS: how much weight should current welfare optimization assign to future generations? This is an ethical, not technical, question — but it determines the entire numerical conclusion.

3.3 Environmental Valuation Methods (Sample-Exam Q32)

Revealed preference: infers value from observed market behavior. Stated preference: directly asks. The sample exam tests this matching.

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4. Mitigation vs. Adaptation (Lecocq & Shalizi 2007)

4.1 Definitions

They are PARTIAL SUBSTITUTES. More mitigation → less future warming → less adaptation needed. But the 30-50 year atmospheric response lag means CURRENT adaptation is needed regardless of mitigation ambition.

4.2 Autonomous vs. Planned Adaptation

4.3 Development-as-Adaptation vs. Climate-Proofing

• Development-as-adaptation: improve general resilience through income, health, education.
• Climate-proofing: build specific defenses against identified hazards.
• Nepal NAPA/LAPA/CAPA blends both schools.

4.4 Some Interventions Do Both

Mangrove/wetland restoration: sequesters carbon (mitigation) AND buffers storm surge (adaptation). Florida coastal wetlands alone remove ~31 million metric tons CO₂/yr. Methane emissions (more potent per molecule) partially offset.

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5. Vulnerability of Poorer Nations (World Bank 2010)

5.1 Three Compounding Vulnerabilities

1. Higher physical exposure — tropics, coasts, drought-prone zones.
2. Higher economic sensitivity — agriculture-dependent economies tied to rainfall/temperature.
3. Lower adaptive capacity — less capital, weaker institutions, limited insurance/technology.

5.2 Coping Strategies and the Honduras Finding

Honduras poorest-quartile asset growth after a climate shock:

• WITH credit/insurance market access: +5.5%
• WITHOUT: −50%

Implication: financial-market development is itself adaptation policy.

5.3 Nepal Case Study

• 2010 NAPA + Climate Change Policy
• 2011: gender recognized as cross-cutting vulnerability
• 2019: gender-responsive LAPAs (Local Adaptation Plans) at village level
• CAPAs at community level
• Five sample groups: women, men, Dalit, marginalized Janajati, well-being groups

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6. International Policy Architecture

6.1 UNFCCC (Rio 1992) — The Framework

• Adopted at the 1992 Rio Earth Summit; in force March 1994
• Non-binding framework treaty — authorizes binding protocols
• Establishes the COP as supreme decision body
• 195+ parties (universal)
• COP1: Berlin, March 1995

6.2 Kyoto Protocol (1997, in force 2005)

Why Kyoto failed:

• US never ratified (Senate 95-0 against, 1997)
• CBDR exempted China and India; their growth overwhelmed Annex I cuts
• No domestic enforcement mechanism

6.3 Montreal Protocol vs. Kyoto Protocol (Sample-Exam Q31f)

Montreal's success rests on narrow scope, identifiable producers, and available substitutes. Kyoto faced a much harder problem.

6.4 CBDR & RC (Hussen pp. 228, 230-231)

Common But Differentiated Responsibilities & Respective Capabilities — the foundational equity principle:

1. Developed nations generated the cumulative atmospheric GHG load
2. They have greater financial/technical capacity
3. Climate damages fall disproportionately on poor nations

Under Kyoto: Annex I = binding; non-Annex I = no targets. Under Paris: CBDR preserved in principle; all countries submit NDCs with differentiated expectations.

6.5 Paris Agreement / COP21 (2015)

Ratchet mechanism: each 5-year NDC must be at least as ambitious as the prior. Procedural substitute for binding top-down targets.

6.6 Brazil Case Study (Sample-Exam)

• NDC: 53% emission reduction by 2030 (vs. 2005 baseline)
• Net-zero by 2050
• Also addresses water, energy, food, social, environmental security and climate resilience
• Cost: ~$1.4 trillion 2016-2030 (~7% of GDP/yr)
• Brazil is non-Annex I (was not bound by Kyoto)
• September 5, 2023: launched its Sovereign Sustainable Bond Framework — can issue green, social, and sustainability bonds
• Ranked first regionally for corporate green bond issuances

6.7 US Domestic Climate Policy

Clean Power Plan (CPP) — Obama-era 2015 EPA rule cutting power-sector CO₂ ~32% below 2005 by 2030. Was the US's main Paris-compliance mechanism. Replaced by weaker Affordable Clean Energy (ACE) rule (2019), then EPA authority curtailed by Supreme Court in West Virginia v. EPA (2022). Demonstrates US climate policy's political fragility.

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7. Clean Technologies & Sustainability Typology

7.1 The Three Categories

7.2 Green Hydrogen (Electrolyser)

• Water (H₂O) is split into hydrogen (H₂) and oxygen (O₂)
• Splitting done by an ELECTROLYSER powered by renewable electricity
• Hydrogen is captured as a clean fuel (combustion produces only water)
• Strongly sustainable when inputs are renewable
• Critical for hard-to-abate sectors: steel, fertilizer, long-distance transport

7.3 Clean-Energy Incentives — EU vs. US

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8. Exam-Ready Key Takeaways

1. IPCC vs. UNFCCC definitions — natural variability vs. human-only attribution.
2. Greenhouse effect: sunlight → IR → GHGs trap → re-radiate → warming; without = −18°C.
3. CO₂ dominates because of abundance and residence time, not per-molecule strength.
4. Carbon × 3.67 = CO₂; 2021 = ~36.3 Gt CO₂ ≈ 40.8 Gt CO₂eq.
5. IPCC: 1988, WMO + UNEP, 195 countries, assesses (not researches), every 5-7 years.
6. MDC = MCC is optimal; tipping points break the smooth optimization.
7. Stern vs. Nordhaus — discount rate ethics drives the entire conclusion.
8. Revealed preference = hedonic; stated preference = contingent valuation.
9. Mitigation vs. adaptation (Lecocq & Shalizi 2007); partial substitutes.
10. Autonomous vs. planned (Thames Barrier); development-as-adaptation vs. climate-proofing (Nepal).
11. Three vulnerability drivers: exposure, sensitivity, adaptive capacity (World Bank 2010).
12. Honduras finding: market access → +5.5% asset growth vs. −50% without.
13. UNFCCC (1992) — framework treaty; COP = supreme body; COP1 Berlin 1995.
14. Kyoto (1997/2005) — 5.2% below 1990, Annex I only, world ended +6%; CDM/ERUs/CERs.
15. CBDR & RC — cumulative responsibility + capacity; Annex I differentiation.
16. Montreal vs. Kyoto — Montreal narrow + substitutable = success; Kyoto comprehensive = harder.
17. Paris (2015) — bottom-up, all countries, 2°C / aspirational 1.5°C, INDCs/NDCs, 5-year ratchet.
18. Brazil NDC: 53% by 2030 vs. 2005 + net-zero 2050; non-Annex I; Sovereign Sustainable Bond Framework Sept 2023.
19. US CPP — Obama 2015 EPA rule → replaced by ACE 2019 → curtailed WV v. EPA 2022.
20. Clean tech: renewables and carbon removal = strongly sustainable; geoengineering = weakly sustainable.
21. Green hydrogen = water split via electrolyser; H₂ captured for energy.
22. EU feed-in tariffs vs. US PTC/ITC tax credits.
23. Mangrove/wetland restoration does BOTH (mitigation + adaptation); methane emissions partly offset.