Climate change Study Guide

📖 Core Concepts Anthropogenic climate change – human‑driven rise in global average surface temperature since the Industrial Revolution. Global warming vs. climate change – warming = temperature rise; climate change = warming + changes in precipitation, storms, ecosystems. Radiative forcing – imbalance between absorbed solar radiation and emitted infrared radiation; greenhouse gases (CO₂, CH₄, N₂O) produce a positive forcing. Carbon budget – total amount of CO₂ that can still be emitted while staying below a temperature target (≈ 900 Gt CO₂ for a 2 °C limit). Climate feedbacks – processes that amplify (water‑vapour, ice‑albedo, permafrost) or dampen (some cloud/vegetation) the initial warming. Tipping points – thresholds (e.g., Greenland Ice Sheet melt at 1.7‑2.3 °C) that, once crossed, trigger irreversible change. 📌 Must Remember Observed warming: +1.5 °C since pre‑industrial (1850–1900). Warming rate: ≈ 0.2 °C per decade over recent decades. CO₂ increase: 50 % since 1750; now > 410 ppm, levels unseen for > 14 Myr. Methane lifetime: 12 yr; concentration ↑ 164 % since 1750. IPCC 2100 scenarios: Low emissions → 1.0‑1.8 °C warming Intermediate → 2.1‑3.5 °C High → 3.3‑5.7 °C Sea‑level rise: 4.8 cm per decade (2014‑2023); 2100 projection 32‑101 cm (high emissions up to 2 m). Carbon budget for 2 °C: 900 Gt CO₂ (≈ 16 yr of current emissions). Net‑zero goal: Global CO₂ emissions ≈ 0 by 2070 to stay < 2 °C. 🔄 Key Processes Greenhouse‑gas forcing: Emission → atmospheric concentration ↑ → infrared absorption ↑ → surface warming. Water‑vapour feedback: Warm air → holds more H₂O → H₂O is a strong GHG → further warming. Ice‑albedo feedback: Ice melt → darker surface exposed → solar absorption ↑ → more melt. Permafrost carbon release: Thaw → organic matter decomposes → CO₂ + CH₄ released → amplifies warming. Carbon budgeting calculation: Remaining budget = (Target temperature – current temperature) / climate sensitivity × cumulative emissions per °C. 🔍 Key Comparisons CO₂ vs. CH₄: CO₂: long‑lived (centuries), larger cumulative emissions, primary driver of long‑term warming. CH₄: short‑lived (≈ 12 yr), 28‑34× higher global warming potential over 100 yr, dominates near‑term forcing. Fossil‑fuel combustion vs. Deforestation: Combustion: direct CO₂ release from energy use. Deforestation: releases stored carbon and removes a carbon sink. Physical climate models vs. Integrated assessment models (IAMs): Physical models: simulate atmosphere‑ocean‑land processes from first‑principles. IAMs: add socioeconomic pathways to estimate future emissions and mitigation costs. ⚠️ Common Misunderstandings “The Sun is causing warming.” → Satellite data show no long‑term increase in solar irradiance since 1880. “Aerosols offset all warming.” → Aerosol cooling peaked in the 1990s; recent reductions have revealed the full greenhouse‑gas signal. “Sea‑level rise stops after net‑zero.” → Thermal expansion and ice‑sheet melt continue for centuries. 🧠 Mental Models / Intuition Thermostat analogy: Greenhouse gases act like adding insulation to a house—less heat escapes, so interior temperature rises. Positive feedback loop: Think of a microphone too close to a speaker; a small sound (initial warming) gets amplified repeatedly (feedbacks). 🚩 Exceptions & Edge Cases Land‑surface albedo change: Converting dark forests to light grasslands can cause a modest cooling effect, but net impact is still warming because carbon loss dominates. Cloud feedbacks: While most clouds give a net positive feedback, some low‑level clouds can reflect sunlight and produce a slight cooling; the balance is model‑dependent. 📍 When to Use Which Estimate future temperature: Use IPCC scenario ranges (low, intermediate, high) depending on policy assumptions. Choose mitigation pathway: If rapid decarbonization possible → prioritize clean energy, phasing out fossil subsidies. If emissions linger → incorporate large‑scale CDR (afforestation, BECCS). Select modeling tool: Need physical climate response → use Earth‑system model. Need policy‑impact assessment → use IAM. 👀 Patterns to Recognize “Warming × 2 → Impact × 4” – Many impacts (heat‑related mortality, extreme‑event frequency) rise faster than temperature. Regional amplification: Arctic warming ≈ 3‑4× global mean; land warming ≈ 2× ocean. Feedback cascade: Once permafrost begins to thaw, methane release accelerates, which speeds further thawing. 🗂️ Exam Traps Distractor: “Solar irradiance has increased 30 % since 1880.” – Wrong; satellite data show no trend. Near‑miss answer: “Aerosols are the main cause of the observed 1.5 °C warming.” – Incorrect; aerosols have a cooling effect that partially masks greenhouse‑gas warming. Confusing “global warming” with “climate change.” – Remember: warming = temperature rise; climate change = warming + broader system changes. Misreading carbon budget: “900 Gt CO₂ is the total emissions to date.” – It is the remaining budget after 2023 for a 2 °C target. --- Use this guide for quick recall before the exam—focus on the bolded numbers, the cause‑effect loops, and the decision rules for mitigation vs. adaptation.