SECTION 4 — CLIMATE CHANGE & ENVIRONMENTAL DISASTERS

1. Conceptual Framework & Definitions

• Weather vs. Climate:
  • Weather: The day-to-day, short-term atmospheric conditions (temperature, humidity, precipitation, wind velocity, atmospheric pressure) observed at a specific time and location.
  • Climate: The long-term average statistical pattern of weather parameters, atmospheric variability, and extreme events observed over an extended period—defined by the World Meteorological Organization (WMO) as 30 years or more.
• Climate Change: A significant, long-term shift in global or regional climate patterns, surface temperatures, and precipitation regimes driven by both natural climate variability and anthropogenic activities that alter the Earth's atmospheric composition.
• Global Warming: The specific component of climate change referring to the long-term rise in Earth's average surface temperature, primarily caused by human activities (fossil fuel combustion, deforestation, industrial processes) since the Pre-Industrial Era (1850–1900 baseline).

WEATHER VS. CLIMATE VS. GLOBAL WARMING

                     ATMOSPHERIC DYNAMICS
                              │
     ┌────────────────────────┼────────────────────────┐
     ▼                        ▼                        ▼
  WEATHER                  CLIMATE               GLOBAL WARMING
• Short-term state      • Long-term average      • Long-term increase in
• Hours / Days / Weeks    (30+ years baseline)     Earth's surface temp
• Highly variable       • Regional/Global trends • Driven by anthropogenic
                        • Statistically stable     greenhouse gases (GHGs)

2. The Greenhouse Effect & Atmospheric Energy Balance

A. Natural vs. Enhanced (Anthropogenic) Greenhouse Effect

• Natural Greenhouse Effect: A fundamental planetary mechanism that traps thermal radiation emitted from Earth's surface. Without natural greenhouse gases (GHGs), Earth's average surface temperature would be approximately -18°C (255 K), freezing the oceans and making life unviable. The natural greenhouse effect raises Earth's average surface temperature to a habitable +15°C (288 K)—providing a natural warming boost of ~33°C.
• Enhanced (Anthropogenic) Greenhouse Effect: The rapid accumulation of human-emitted GHGs in the atmosphere since 1850, which traps excessive outgoing longwave thermal infrared radiation and creates a global thermal energy imbalance (positive radiative forcing).

EARTH'S ATMOSPHERIC ENERGY BALANCE & GREENHOUSE EFFECT

Incoming Shortwave Solar Radiation (100%)
                 │
                 ├─► ~30% Reflected back to space (Earth's Albedo: Clouds, Aerosols, Ice/Snow)
                 └─► ~70% Absorbed by Atmosphere (~20%) and Earth's Surface (~50%)
                                 │
                                 ▼
                     Earth's Surface Warms & Re-emits
                     Outgoing Longwave Infrared Radiation (Terrestrial Radiation)
                                 │
                                 ▼
        Greenhouse Gas Molecules (CO₂, CH₄, N₂O, H₂O) Absorb Outgoing IR
                                 │
                                 ▼
       Re-radiate Thermal Energy in All Directions (Including back to Earth's Surface)
                                 │
                                 ▼
                     Global Surface Warming

B. Atmospheric Windows & Absorption Spectra

• Earth emits thermal infrared radiation primarily in the wavelength band of 4 to 100 micrometers (µm).
• Atmospheric Window (8–13 µm): A narrow band in the thermal infrared spectrum where natural atmospheric gases (water vapor and \(\text{CO}_2\)) absorb relatively little outgoing radiation, allowing thermal energy to escape into space.
• Window Closure by Synthetic Gases: Fluorinated gases (CFCs, HCFCs, HFCs, \(\text{SF}_6\)) absorb strongly within the 8–13 µm window, making them potent greenhouse gases per molecule.

3. Major Greenhouse Gases (GHGs) & Radiative Forcing Metrics

MAJOR GREENHOUSE GASES & RELATIVE ATMOSPHERIC CONTRIBUTION

               CONTRIBUTION TO ENHANCED GREENHOUSE EFFECT
                                   │
  ┌─────────────────┬──────────────┼──────────────┬─────────────────┐
  ▼                 ▼              ▼              ▼                 ▼
Water Vapor (H₂O)  Carbon Dioxide  Methane (CH₄)  Nitrous Oxide     Fluorinated Gases
• Most abundant    • Main driver   • Short-lived  • Long-lived      • Synthetic / Potent
• Positive feedback• Fossil fuels  • Agriculture  • Fertilizers     • High GWP
  loop               & land clearance & livestock   & industry        • SF₆, HFCs, PFCs

A. Global Warming Potential (GWP) & Radiative Forcing

• Radiative Forcing (RF): The net change in Earth's energy balance (measured in Watts per square meter, \(\text{W/m}^2\)) caused by a driver relative to the pre-industrial baseline (1750). Positive RF causes warming; negative RF causes cooling.
• Global Warming Potential (GWP): A standardized metric defined by the IPCC comparing the heat-trapping capacity of 1 kg of a specific gas relative to 1 kg of Carbon Dioxide (\(\text{CO}_2\)) over a specified time horizon (typically 100 years, GWP₁₀₀).

4. Global Carbon Budget, Sinks & Feedback Loops

A. Global Carbon Cycle & Carbon Sinks

• Global Carbon Budget: The cumulative maximum amount of net global \(\text{CO}_2\) that can be emitted into the atmosphere while maintaining a reasonable probability of limiting global warming to a specific threshold (e.g., 1.5°C or 2.0°C above pre-industrial levels under the Paris Agreement).
• Carbon Sink: Any natural or artificial reservoir that absorbs and stores more carbon from the atmosphere than it releases (e.g., oceans, forests, peatlands, soil).

THE GLOBAL CARBON SINKS & PARTITIONING

                   ANNUAL HUMAN CO₂ EMISSIONS (~100%)
                                   │
     ┌─────────────────────────────┼─────────────────────────────┐
     ▼                             ▼                             ▼
Atmospheric Accumulation        Ocean Sink                    Terrestrial / Land Sink
• Absorbs ~46% of emissions    • Absorbs ~26% of emissions   • Absorbs ~28% of emissions
• Drives rising atmospheric    • Drives ocean acidification  • Forests, soils, peatlands,
  CO₂ concentrations (426+ ppm)  (Decreasing marine pH)        & photosynthesis

B. Climate Feedback Loops

• Positive Feedback Loops (Amplifying Warming):
  1. Ice-Albedo Feedback: Rising temperatures melt polar sea ice and glaciers \(\rightarrow\) Dark ocean/land replaces reflective white ice \(\rightarrow\) Surface albedo drops \(\rightarrow\) More solar energy is absorbed \(\rightarrow\) Accelerates melting.
  2. Water Vapor Feedback: A warmer atmosphere holds more water vapor (Clausius-Clapeyron relation: ~7% increase per 1°C warming) \(\rightarrow\) Water vapor is a potent GHG \(\rightarrow\) Traps additional heat.
  3. Permafrost Thaw Feedback: Warming melts Arctic permafrost \(\rightarrow\) Anaerobic decomposition releases locked \(\text{CH}_4\) and \(\text{CO}_2\) \(\rightarrow\) Amplifies global warming.
• Negative Feedback Loops (Dampening Warming):
  1. \(\text{CO}_2\) Fertilization Effect: Elevated atmospheric \(\text{CO}_2\) stimulates plant photosynthetic rates in some terrestrial ecosystems, temporarily increasing carbon uptake.

5. Historical Surface Temperature Trajectory & Key Baselines

GLOBAL TEMPERATURE ANOMALY TRAJECTORY (1850–PRESENT)

  Pre-Industrial Baseline (1850–1900) ──► 0°C Anomaly Baseline
                                                 │
  Current Observed Warming (2024–2026) ──► +1.2°C to +1.45°C Global Surface Warming
                                                 │
  Paris Agreement Statutory Target     ──► Well below 2.0°C, pursuing 1.5°C Limit

• Pre-Industrial Baseline: Defined by the IPCC as the period 1850–1900, representing global atmospheric conditions prior to widespread fossil fuel combustion.
• Observed Global Warming: Earth's average surface temperature has increased by ~1.2°C to 1.4°C above the pre-industrial baseline, with the last decade being the warmest on record.
• The 1.5°C Threshold: IPCC AR6 reports warn that breaching 1.5°C warming significantly increases the risk of triggering irreversible ecological "tipping points" (e.g., West Antarctic Ice Sheet collapse, Amazon Rainforest dieback, coral reef mortality >90%).

6. Comprehensive Summary Matrix: Climate Change Basics

Quick Revision

• Weather vs. Climate: Weather is short-term; climate is the 30-year statistical average.
• Natural Greenhouse Effect: Keeps Earth at a habitable +15°C instead of a frozen -18°C.
• Pre-Industrial Baseline: 1850–1900 period used by IPCC.
• Current Atmospheric \(\text{CO}_2\): Exceeds 425 ppm (up from 280 ppm pre-industrial).
• Radiative Forcing: Net energy imbalance measured in Watts per square meter (\(\text{W/m}^2\)).
• GWP Baseline: Carbon Dioxide (\(\text{CO}_2\)) has a GWP of 1.
• Methane (\(\text{CH}_4\)): GWP₁₀₀ = 27.9; lifetime ~12 years; key sources include livestock and rice paddies.
• Highest GWP Gas: Sulphur Hexafluoride (\(\text{SF}_6\)) with a GWP of 25,200 and ~3,200-year lifetime.
• Carbon Sink Partitioning: Oceans absorb ~26%, land ecosystems absorb ~28%, and ~46% accumulates in the atmosphere.
• Core Feedback Loops: Ice-Albedo, Water Vapor, and Permafrost Thaw feedback loops accelerate global warming.

Memory Map

1. Atmospheric Baseline & Physics ──► WMO 30-Yr Climate Rule ──► Natural +15°C vs. -18°C ──► 1850–1900 Pre-Industrial Baseline ──► Current \(\text{CO}_2\) > 425 ppm.

2. GHG Hierarchy & GWPs ──► \(\text{CO}_2\) (GWP 1) ──► \(\text{CH}_4\) (GWP ~28) ──► \(\text{N}_2\text{O}\) (GWP 273) ──► Fluorinated Gases (HFCs/PFCs/\(\text{NF}_3\)) ──► \(\text{SF}_6\) (GWP 25,200).

3. Carbon Sinks & Positive Feedbacks ──► Sinks: Atmosphere (46%), Land (28%), Ocean (26%) ──► Feedbacks: Ice-Albedo, Water Vapor, Permafrost Thaw.

Must Remember

• Natural vs. Enhanced Effect: Natural greenhouse effect warms Earth by ~33°C (from -18°C to +15°C).
• Highest GWP Gas: Sulphur Hexafluoride (\(\text{SF}_6\)) has the highest GWP₁₀₀ (25,200).
• \(\text{CO}_2\) Concentration: Increased from ~280 ppm (pre-industrial) to over 425 ppm.
• Water Vapor: The most abundant natural greenhouse gas, acting as a major positive feedback driver.
• Primary Oceans Function: Oceans absorb ~26% of human \(\text{CO}_2\) emissions, causing ocean acidification.

Key Terms

• Global Warming Potential (GWP): A measure of how much heat a greenhouse gas traps in the atmosphere relative to \(\text{CO}_2\) over a specific time horizon.
• Radiative Forcing: The net change in Earth's energy balance caused by human or natural drivers, measured in \(\text{W/m}^2\).
• Ice-Albedo Feedback: A positive feedback loop where melting ice reduces surface reflectivity, accelerating heat absorption and further melting.
• Permafrost Thaw: The melting of permanently frozen Arctic soil, releasing locked methane and carbon dioxide into the atmosphere.
• Atmospheric Window: The 8–13 µm wavelength band through which thermal infrared radiation escapes into space.

1-Line Bits / Short Points

• Climate is defined by the World Meteorological Organization as the statistical average of weather over 30 years or more.
• Without the natural greenhouse effect, Earth's average surface temperature would be approximately -18°C.
• The pre-industrial baseline used by the IPCC to measure global warming is 1850–1900.
• Current atmospheric carbon dioxide levels exceed 425 ppm compared to the pre-industrial level of 280 ppm.
• Carbon dioxide serves as the baseline reference gas with a Global Warming Potential (GWP) of 1.
• Methane has a 100-year Global Warming Potential (GWP₁₀₀) of approximately 28.
• Nitrous Oxide has a GWP₁₀₀ of 273 and an atmospheric lifetime of over 100 years.
• Sulphur Hexafluoride (\(\text{SF}_6\)) has the highest Global Warming Potential of 25,200.
• Oceans absorb approximately 26% of human carbon dioxide emissions, driving ocean acidification.
• Terrestrial ecosystems (forests and soil) absorb approximately 28% of global carbon emissions.
• The Clausius-Clapeyron relation states that the atmosphere holds ~7% more water vapor per 1°C rise in temperature.