3.2. Greenhouse Effect (B2)

The natural greenhouse effect traps infrared radiation emitted by Earth's surface, keeping the planet’s average temperature warm enough to support liquid water and life.
Greenhouse gases like CO₂, CH₄, H₂O, and N₂O absorb and re-emit thermal radiation, maintaining Earth's energy balance.
Human activities (burning fossil fuels, agriculture) increase greenhouse gas concentrations, causing the enhanced greenhouse effect and leading to global warming.

The atmosphere is modelled as a system where incoming solar radiation must balance outgoing terrestrial radiation to maintain thermal equilibrium.
Key factors include solar constant, albedo (reflectivity of Earth), emissivity, and the greenhouse effect affecting energy absorption and re-emission.
Energy balance models use conservation of energy to predict Earth's mean surface temperature and assess climate changes.

Conservation of energy
Emissivity defined
Albedo defined
Earth’s albedo variably daily and by latitude
The solar constant
Incoming radiative power is dependent on the projected surface of a planet along the direction of the path of the rays, resulting in a mean value
That methane CH4, water vapour H2O, carbon dioxide CO2, and nitrous oxide N2O, are the main greenhouse gases and each of these has origins that are both natural and created by human activity
The absorption of infrared radiation by the main greenhouse gasesin terms of the molecular energy levels and the subsequent emission of radiation in all directions
The greenhouse effect explained in terms of both a resonance model and molecular energy levels
The augmentation of the greenhouse effect due to human activities is known as the enhanced greenhouse effect.

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