- Describe the mechanism of the enhanced greenhouse effect step by step.
- Rank the greenhouse gases by source, abundance and global warming potential.
- Calculate and reduce a personal, national or product carbon footprint.
- Evaluate the mitigation options available to a country such as Egypt.
🌳 Concept tree
Greenhouse Effect and Carbon Footprint
├── Energy balance of the planet
│ ├── Incoming short-wave solar radiation
- │ ├── Reflected (albedo about 30%) and absorbed (about 70%)
- │ └── Outgoing long-wave infrared from the surface
├── The greenhouse mechanism
│ ├── GHGs transmit the incoming radiation
- │ ├── They absorb and re-emit the outgoing infrared
- │ └── The lower atmosphere and surface become warmer
├── The gases
- │ ├── Water vapour (largest natural effect, not directly controlled)
- │ ├── CO₂ (fossil fuels, cement, deforestation) — the reference gas
│ ├── CH₄ (rice, ruminants, landfills) GWP ≈ 28
│ ├── N₂O (fertilisers) GWP ≈ 265
- │ ├── O₃ (photochemical) and CFCs (GWP up to 10,000+)
├── Carbon footprint│ ├── Primarydirect emissions from burning fuel
│ ├── Secondaryemissions of the electricity and goods consumed
│ ├── Unitskg or t CO₂-equivalent per year
│ └── Offsetting, cap-and-trade, carbon tax
└── Solutions├── Mitigationenergy, transport, industry, agriculture
├── Adaptationcoasts, water, crops, health
└── International agreementsUNFCCC, Kyoto, Paris, COP
- Solar radiation reaches the Earth mainly as visible and near-infrared short waves, which pass through the atmosphere almost unabsorbed.
- About 30% is reflected back to space by clouds, dust and bright surfaces (the albedo) and about 70% is absorbed by the surface and warms it.
- The warmed body then radiates according to its own temperature — at about 288 K the peak is near 10 µm, in the long-wave infrared.
- Greenhouse molecules absorb particular infrared bands because their vibrations change the dipole moment of the molecule; they then re-emit the energy in random directions, so part of it returns to the surface.
- The result is that the surface and the lower atmosphere are warmer than they would be in radiative balance with space: about 33 °C warmer than a bare blackbody Earth.
- The enhanced greenhouse effect is the additional warming produced when human activity raises the concentration of these gases; between 1750 and today CO₂ has gone from 280 to more than 420 ppm and the mean surface temperature has risen about 1.1 °C.
- Windows of transparency the atmosphere lets visible light in and lets some infrared out, but absorption bands of CO₂, H₂O and CH₄ close part of the infrared window — that closure is the physical cause of the effect.
| Comparison aspect | Main idea | Keywords |
|---|
| Water vapour (H₂O) | - contributes most of the natural greenhouse effect
- but its amount is set by temperature
- not directly by emission
- so it acts as a feedback
- not a forcing
| contributesmostnaturalgreenhouse |
| Carbon dioxide (CO₂) | - from the combustion of coal
- oil and gas
- from cement manufacture (CaCO₃ → CaO + CO₂) and from deforestation. Responsible for roughly two thirds of the human forcing
- it stays in the atmosphere for a century or more
| combustioncoalcementmanufacture |
| Methane (CH₄) | - rice paddies under water
- ruminant digestion
- landfills
- coal mines and gas leaks
- GWP ≈ 28 over 100 years
- lifetime about 12 years
| ricepaddiesunderwater |
| Nitrous oxide (N₂O) | - nitrogen fertilisers and biomass burning
- GWP ≈ 265
- lifetime over a century
- and it also destroys ozone
| nitrogenfertilisersbiomassburning |
| Ozone (O₃) | in the troposphere: formed secondarily from NOx, carbon monoxide and hydrocarbons in sunlight. | troposphereformedsecondarilycarbon |
| CFCs, HCFCs and their substitutes | - GWP in the thousands
- hydrofluorocarbons (HFCs) do not harm ozone but are strong greenhouse gases
- which is why the Kigali Amendment phases them down
| thousandshydrofluorocarbonsHFCsharm |
Carbon footprint: definition, calculation and units
Carbon footprint: definition, calculation and units
| Comparison aspect | Main idea | Keywords |
|---|
| • | - The carbon footprint is the total amount of greenhouse gases released directly or indirectly by an individual
- an organisation
- an event or a product
- expressed in tonnes of CO₂-equivalent (t CO₂e) per year so that all gases are comparable
| carbonfootprinttotalamount |
| Primary (direct) footprint | - fuel burnt on site — petrol in a car
- gas for heating and cooking
- diesel in machinery
| fuelburntsitepetrol |
| Secondary (indirect) footprint | - emissions of the power stations that supply the electricity
- plus everything embedded in the goods and services consumed
- the transport of food and the treatment of waste
| emissionspowerstationssupply |
| Typical factors | - petrol about 2.3 kg CO₂ per litre
- diesel 2.7
- natural gas about 0.19 kg per kWh of heat
- grid electricity from 0.1 to 0.9 kg CO₂ per kWh depending on the fuel mix
- a return flight London–Cairo roughly 0.5–0.7 t CO₂ per passenger
| petrollitredieselnatural |
| • | - Global average footprint ≈ 4.7 t CO₂e per person
- high-income countries 8–15 t
- Egypt about 2.3–2.5 t per person
- well below the world average
- which is the ethical core of the climate-justice argument
| GlobalaveragefootprintCO₂e |
| Carbon trading and carbon tax | - a cap is set and permits are bought and sold
- or a price is placed on each tonne
- so that reducing emissions becomes the cheaper option for a firm
| permitsboughtsoldprice |
Worked calculation
- A household burns 1,200 L of petrol a year in a car, uses 3,000 kWh of electricity from a grid emitting 0.45 kg CO₂/kWh, and 150 m3 of natural gas (about 0.2 kg CO₂/m3 × 10.5 kWh/m3, i.e. roughly 32 kg per m3).
- Direct and indirect emissions: 1,200 × 2.3 = 2,760 kg; 3,000 × 0.45 = 1,350 kg; 150 × 2.1 ≈ 315 kg (as heat) — total ≈ 4.4 t CO₂e a year.
| Comparison aspect | Main idea | Keywords |
|---|
| Sea-level rise | - of 0.15–0.20 m since 1900
- from thermal expansion and melting ice
- threatening low-lying coasts and deltas
- including the Nile Delta
- and pushing salt water into the aquifer
| since1900thermalexpansion |
| Changes in the water cycle | - wet regions wetter
- dry regions drier
- more evaporation from reservoirs
- and a higher probability of both flash floods and drought
| regionswetterdrierevaporation |
| Agriculture | - heat stress shortens the grain-filling period of wheat and maize
- and higher CO₂ raises yield only where water and nutrients are not limiting
| heatstressshortensgrain |
| Ecosystems | - coral bleaching above 1–2 °C of warming
- shifting of species ranges
- and loss of the least mobile ones
- the more diverse an ecosystem
- the better it resists change
| coralbleachingabovewarming |
| Health | - heat stroke
- wider distribution of vector-borne disease
- and reduced air quality as warm nights increase ozone formation
| heatstrokewiderdistribution |
| Cryosphere | - glaciers retreat first
- reducing dry-season river flow
- before they disappear altogether
| glaciersretreatfirstreducing |
Mitigation — attacking the cause
| Comparison aspect | Main idea | Keywords |
|---|
| • | - Energy efficiency in buildings
- industry and appliances
- district heating
- waste-heat recovery
| Energyefficiencybuildingsindustry |
| • | - Renewable electricity and heat
- with storage and grid interconnection (see the companion lesson on renewable energy and green hydrogen)
| Renewableelectricityheatstorage |
| Transport | - mass transit
- electric vehicles charged from clean power
- cycling and walking
- rail freight
- and efficient shipping and aviation fuels
| masstransitelectricvehicles |
| Industry | - green steel and cement chemistry
- capture at process sources
- circular economy and recycling
- which reduces the emission embedded in new material
| greensteelcementchemistry |
| Agriculture and land use | - water management in rice
- better manure handling
- reduced food waste
- and afforestation and protection of existing forests and wetlands as sinks
| watermanagementricebetter |
Adaptation — living with the effect
| Comparison aspect | Main idea | Keywords |
|---|
| • | - Coastal defence with sea walls
- breakwaters and beach nourishment
- controlled retreat from the most exposed land
| Coastaldefencewallsbreakwaters |
| Water | - canal lining
- modern irrigation
- treated-waste-water re-use
- desalination and rainwater harvesting
| canalliningmodernirrigation |
| Crops | - heat- and salt-tolerant varieties
- shifted planting dates
- resilient seed banks and insurance for smallholders
| heatsalttolerantvarieties |
| Cities | - cool roofs
- green corridors
- drainage sized for extreme rain
- and early-warning systems for heat waves
| coolroofsgreencorridors |
| The agreements | the UNFCCC (1992) set the framework; the Kyoto Protocol (1997) bound only industrialised countries; the Paris Agreement (2015) made pledges universal (NDCs) with a long-term goal of well below 2 °C and efforts toward 1.5 °C; COP27 (Sharm El-Sheikh, 2022) created the loss-and-damage fund; adaptation goals and the phase-down of HFCs and coal follow in later decisions. | UNFCCC1992frameworkKyoto |
- Why does CO₂ absorb infrared while N₂ does not? — CO₂ is a linear molecule whose asymmetric stretch and bending change its dipole moment, so it interacts with the radiation; N₂ is symmetric homonuclear and its vibration produces no dipole change.
- A country produces 12 million tonnes of cement. With about 0.8 t CO₂ per tonne of clinker, estimate the process emission. — ≈ 9.6 Mt CO₂, mostly from calcination, not from fuel.
- CO₂, CH₄, N₂O, CFC-12. — CO₂ = 1 < CH₄ ≈ 28 < N₂O ≈ 265 < CFC-12 ≈ 10,000.
- A family replaces 40 halogen bulbs of 60 W by 9 W LEDs running 5 h a day. Find the annual cut if the grid emits 0.45 kg CO₂/kWh. — Saving = 40 × 51 W × 5 h × 365 = 372 kWh ⟹ ≈ 167 kg CO₂ a year.
- Explain how melting Arctic sea ice accelerates warming. — Bright ice reflects most sunlight; when it is replaced by dark ocean, absorption rises, the water warms, more ice melts — a positive albedo feedback.
| Comparison aspect | Main idea | Keywords |
|---|
| The greenhouse effect itself is natural and necessary | the problem is its enhancement. Answers that say “the greenhouse effect is a pollution” lose the mark | problemenhancementAnswerspollution |
| CO₂ is not the strongest absorber per molecule | it is the most important because of the quantity emitted and its lifetime | mostimportantbecausequantity |
| Water vapour is a greenhouse gas but not a Kyoto gas | - it is controlled by temperature
- not emitted directly
| controlledtemperatureemitteddirectly |
| Footprint is CO₂-equivalent | - not only CO₂
- do not omit methane and nitrous oxide
| omitmethanenitrousoxide |
| Primary vs secondary | electricity used at home is a secondary (indirect) emission even though the meter is at your house | electricityusedhomeindirect |
| Albedo changes are feedbacks | not forcings — they amplify the original change | forcingsamplifyoriginal |
| Adaptation ≠ mitigation | - sea walls adapt
- renewables mitigate. Questions ask to classify actions
| wallsrenewablesmitigateQuestions |
