Introduction to the atmosphere

The troposphere is the lowest layer of the atmosphere (about 0–12 km) where weather occurs and most water vapour is found.

The troposphere (weather, life, greenhouse effect) and the stratosphere (ozone layer, UV protection) are most commonly tested because they directly affect living systems.

The greenhouse effect is the process where greenhouse gases absorb and re-emit long-wave radiation, warming the lower atmosphere.

In the troposphere (0–12 km), temperature decreases with altitude and weather occurs.

It contains almost all water vapour and is where weather and atmospheric mixing occur, supporting ecosystems and the water cycle.

The stratosphere is the layer from about 12–50 km that contains the ozone layer. Temperature increases with altitude because ozone absorbs UV radiation.

In the stratosphere (12–50 km), temperature increases with altitude due to UV absorption by ozone.

Temperature decreases with altitude by about 6.5°C per km in the troposphere.

Atmospheric pressure helps maintain liquid water at Earth’s surface; without enough pressure, water would evaporate or freeze more easily.

Nitrogen (N₂) is about 78% and oxygen (O₂) is about 21% of the atmosphere.

The stratosphere provides UV protection because the ozone layer absorbs harmful UV-B and UV-C radiation.

Carbon dioxide (CO₂), water vapour (H₂O), and methane (CH₄).

Even in small concentrations, greenhouse gases like CO₂, H₂O, and CH₄ absorb and re-emit long-wave radiation, strongly influencing Earth’s temperature.

Name a function (e.g., greenhouse effect, ozone absorption, oxygen supply) and immediately link it to an outcome for life (e.g., liquid water, reduced DNA damage, respiration).

The greenhouse effect mainly operates in the troposphere to warm Earth by trapping long-wave radiation, while the ozone layer is in the stratosphere and protects life by absorbing UV radiation.

Short-wave radiation warms Earth’s surface, the surface emits long-wave radiation, greenhouse gases absorb some long-wave and re-emit it, warming the lower atmosphere.

Short-wave radiation is higher-energy radiation from the Sun (mainly visible light and UV) that can pass through the atmosphere.

Earth’s climate depends on the balance between incoming short-wave solar radiation and outgoing long-wave infrared radiation.

Examples include water vapour (H₂O), carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and ozone (O₃).

Greenhouse gases mainly absorb long-wave (infrared) radiation emitted by Earth.

Long-wave radiation is lower-energy infrared radiation emitted by Earth’s surface after it absorbs solar energy.

Albedo is the proportion of incoming solar radiation that is reflected by a surface (high for light surfaces, low for dark surfaces).

Higher albedo reflects more incoming radiation and tends to cool surfaces; lower albedo absorbs more and tends to warm surfaces.

The natural greenhouse effect makes Earth habitable, while the enhanced greenhouse effect is extra warming caused by increased greenhouse gas concentrations from human activities.

Burning fossil fuels increases CO₂ concentration, enhancing heat trapping in the lower atmosphere.

On average, incoming energy must equal outgoing energy (energy in = energy out).

About 33°C colder (around −18°C instead of about +15°C).

Confusing short-wave (incoming solar) with long-wave (outgoing infrared) or mixing the greenhouse effect with the ozone layer.

Sun = short-wave (incoming). Earth = long-wave (outgoing infrared).

Short-wave, long-wave (infrared), absorption, re-emission, greenhouse gases, warming of the lower atmosphere.

Albedo controls how much solar energy is reflected vs absorbed, influencing surface temperature and climate patterns.

Albedo is the proportion of incoming solar radiation reflected by a surface, expressed as a decimal (0–1) or a percentage.

The equator receives more direct sunlight while the poles receive sunlight at a low angle spread over a larger area, so the tropics gain more energy.

Warming → ice melt → lower albedo → more absorption → more warming (positive feedback).

Atmospheric circulation (convection and global wind patterns) and ocean currents (surface and deep circulation).

High albedo: fresh snow/ice. Low albedo: open ocean/dark asphalt.

Heat moves from regions of surplus energy near the equator toward regions of deficit energy near the poles.

Convection is the movement where warm air rises, cools, and sinks, transferring heat and driving circulation and weather.

Warming melts ice, lowering albedo so more solar energy is absorbed, causing more warming and further ice melt (a positive feedback).

It is a positive feedback because the initial warming leads to changes (lower albedo) that amplify the warming.

Convection (atmosphere), ocean currents, and latent heat transfer (evaporation/condensation).

Latent heat is energy absorbed during evaporation and released during condensation, moving heat with water vapour in the atmosphere.

Include both atmospheric (convection/circulation) and oceanic (currents/latent heat) heat redistribution mechanisms.

Link surface colour/type to reflectivity (albedo) and then to energy absorbed and temperature change.

State whether it is positive or negative, then show a clear loop with arrows (cause → effect → amplifies or reduces the cause).