Climate change mitigation Study Guide

📖 Core Concepts Climate‑change mitigation – Human actions that reduce greenhouse‑gas (GHG) emissions or increase carbon sinks. Carbon dioxide removal (CDR) – Anthropogenic techniques that pull CO₂ from the air and store it (e.g., direct‑air capture, biochar, afforestation). Natural uptake is not counted as CDR. Primary mitigation measures – Clean energy (solar, wind, nuclear), energy efficiency, sustainable transport, and land‑use actions (forest protection, soil carbon). Emission‑peak requirement – Global GHG emissions must peak ≤ 2025 and fall ≈ 43 % by 2030 to keep a 1.5 °C pathway alive. Carbon pricing – Tax or cap‑and‑trade schemes that put a monetary cost on each tonne of CO₂ emitted, driving low‑carbon choices. --- 📌 Must Remember 2020 global GHG emissions: 49.8 Gt CO₂‑eq; CO₂ ≈ 72 %, CH₄ ≈ 19 %, N₂O ≈ 6 %, fluorinated gases ≈ 3 %. Fuel‑type shares: Coal 39 %, Oil 34 %, Natural gas 21 %, Cement 4 %. Sector contributions: Electricity/heat/transport 73 % of emissions; Industry 5 %; Waste 3 %; AFOLU ≈ 18 %. Target reductions: Peak ≤ 2025; ‑43 % by 2030 for 1.5 °C. Solar LCOE 2024: US$0.039‑0.041 /kWh (cheapest new bulk electricity in many regions). Heat‑pump COP: 3‑5 ×  electricity input (moves 3–5 kWh heat per kWh electricity). Carbon‑price impact: Makes fossil‑fuel electricity less competitive, spurs renewables. Afforestation potential: > 2,300 Gt CO₂ stored by 2100 (if fully implemented). BECCS negative‑emissions range: 0‑22 Gt CO₂ yr⁻¹ (2018 estimate). --- 🔄 Key Processes Energy‑system decarbonisation Replace coal → natural gas (≈ ½ lifecycle GHG) → renewables (solar, wind, geothermal) → integrate variable renewables with transmission, storage, demand‑side management, sector coupling. Carbon‑sink enhancement Forest protection → prevent deforestation (4.2‑7.4 Gt CO₂‑eq yr⁻¹). Afforestation/reforestation → tree planting → carbon capture in biomass & soils. Soil carbon management → reduced tillage, cover crops, biochar → increase soil organic carbon. Carbon‑dioxide removal (CDR) workflow Capture (DAC, BECCS, direct air capture) → transport → secure storage (geological, ocean, mineralization). Carbon‑pricing implementation Set price per tonne CO₂ → collect revenue → reinvest in renewables, rebates, or climate‑adaptation projects. --- 🔍 Key Comparisons Coal vs. Natural Gas – Coal emits 2× more GHG per kWh; switching cuts lifecycle emissions ≈ 50 % (electricity) or 66 % (heat). On‑shore vs. Offshore Wind – Offshore: higher capacity factor, larger turbines, higher cost; on‑shore: cheaper, more land‑use constraints. Solar PV vs. Wind – Solar cheapest LCOE (2024); wind provides more night‑time/seasonal complementarity (wind peaks in winter). Afforestation vs. Reforestation – Afforestation creates new forest on non‑forested land (higher long‑term storage potential); reforestation restores degraded forest (faster carbon uptake due to existing root/soil carbon). Carbon Tax vs. Emissions Trading – Tax gives price certainty, trading gives emissions‑certainty (cap). --- ⚠️ Common Misunderstandings “All carbon removal is natural” – Only anthropogenic activities (DAC, BECCS, biochar) count as CDR; natural uptake isn’t a mitigation policy. “Natural gas is a clean bridge” – Methane leakage can erase the GHG advantage; infrastructure lock‑in creates stranded‑asset risk. “Renewables alone solve intermittency” – Variable output requires flexible grids, storage, and demand‑side management; otherwise curtailment occurs. “Afforestation automatically sequesters carbon” – Success depends on species, climate, and long‑term protection; poorly sited plantations can be carbon neutral or positive. --- 🧠 Mental Models / Intuition Energy‑flow ladder: Fuel → Heat → Electricity → End‑use. Cutting emissions is easiest by moving up the ladder (e.g., electrify heat, then source electricity from renewables). Carbon‑budget clock: Imagine a fixed “budget” of allowable CO₂; every tonne burned ticks the clock toward 1.5 °C. Prioritize actions that spend the fewest ticks per unit of benefit (high‑impact, low‑cost measures). Supply‑demand balance for renewables: Treat variable renewables like a stock market – supply (generation) fluctuates; demand‑side response and storage act as “trading” to keep the system stable. --- 🚩 Exceptions & Edge Cases Methane leakage – If leakage > 2 %, natural‑gas advantage disappears. Stratospheric aerosol injection (SAI) – Not a mitigation tool; considered a climate‑risk‑reduction with severe side‑effects (ozone loss, termination shock). Biochar carbon accounting – Only 50 % of biomass carbon stays in soil; the rest is emitted during production. Blue carbon (mangroves, seagrasses) – Extremely high per‑area sequestration, but long‑term stability and scalability are still debated. --- 📍 When to Use Which Choose renewable generation when the region has high solar irradiance or wind resources and transmission/storage can be built economically. Deploy natural gas only as a short‑term bridge if methane leak rates are demonstrably low (< 1 %) and the plant can be retired within 10 years. Apply carbon pricing in markets with clear price signals; pair with subsidy reform to avoid double‑counting incentives. Select CDR method based on scale and land‑use: DAC – High‑cost, low land impact, suitable where clean electricity is abundant. Afforestation – Low cost, high land requirement, best in tropical zones. Biochar – Useful when agricultural residues are plentiful. --- 👀 Patterns to Recognize Seasonal complementarity: Solar peaks summer; wind (especially offshore) peaks winter → look for paired deployment in planning questions. Emission source breakdown: 70 %+ of emissions come from energy use → any policy that targets electricity, heat, or transport will have outsized impact. Policy effectiveness curve: Market‑based instruments (price) → high impact in developed economies; regulatory standards → higher impact in developing contexts. Negative‑emissions ceiling: Even aggressive CDR cannot fully offset continued fossil use; look for “phase‑out fossil fuels” as a prerequisite in any mitigation pathway. --- 🗂️ Exam Traps “Renewable energy alone will meet the 1.5 °C target.” – Ignoring the need for rapid fossil‑fuel phase‑out and CDR. Confusing “afforestation” with “reforestation.” – They have different carbon‑storage dynamics and costs. Assuming all methane sources are equal. – Livestock vs. fossil‑fuel fugitive emissions have different mitigation levers. Treating carbon taxes and cap‑and‑trade as interchangeable. – The former guarantees price, the latter guarantees emission ceiling; each has distinct policy design implications. Over‑estimating bioenergy without CCS. – Bioenergy alone can be carbon‑neutral or carbon‑positive if combustion emissions aren’t captured. ---