The Atmosphere, Climate and Climate Change: Dynamics, Radiative Balance and Forcing
This domain assesses atmospheric structure, the planetary energy budget, general circulation, Mediterranean climate dynamics and the distinction between natural and anthropogenic forcing. Numeric or process-based reasoning is common.
Structure and composition
Dry air is roughly 78% N2, 21% O2, 0.93% Ar and about 0.042% CO2; water vapour is variable and is itself a greenhouse gas. Layers: troposphere (weather; environmental lapse rate about 6.5 °C/km), stratosphere (ozone absorbs UV), mesosphere, thermosphere, separated by the tropopause, stratopause and mesopause.
Radiative balance
Incoming solar radiation is about 1361 W/m² at the top of the atmosphere; global albedo is about 30%. Absorbed shortwave is balanced by outgoing longwave radiation, plus latent and sensible heat fluxes. The natural greenhouse effect lifts the mean surface temperature from roughly −18 °C to about +15 °C. Increasing greenhouse gas concentrations raise radiative forcing (W/m²) and perturb the balance.
General circulation
Hadley, Ferrel and Polar cells, the ITCZ, trade winds, westerlies, jet streams and the Coriolis effect. Subtropical high-pressure belts create the Mediterranean summer drought; winter brings Atlantic and Mediterranean frontal rain. In the Balearics, autumn DANA episodes (isolated upper-level depressions, colloquially gota freda) deliver torrential rain.
Forcing and feedbacks
- Natural: Milankovitch cycles (eccentricity ~100 ka, obliquity ~41 ka, precession ~23 ka), solar variability, volcanic aerosols (Pinatubo-type cooling), ENSO.
- Anthropogenic: CO2 from fossil fuels (warming of about 1.1 °C above pre-industrial levels), CH4, N2O and halocarbons, plus land-use change.
- Feedbacks: water vapour (positive), ice-albedo (positive), clouds (uncertain), ocean acidification (chemical, not a feedback but a consequence).
Worked example
Why is Palma's summer dry although the city is coastal? In summer the subtropical high shifts north and dominates the western Mediterranean, producing subsidence that suppresses convection, even though sea-breeze convergence moderates temperatures. Rainfall requires either frontal systems (winter) or upper-level cold air over warm sea water (autumn DANA). Each factor must be attributed to a specific mechanism.
Traps that cost marks
- Confusing ozone depletion (UV) with the greenhouse effect (infrared).
- Confusing weather with climate.
- Claiming Milankovitch cycles explain current warming; they change slowly and are not the driver of the recent trend.
- Stating that a decrease in albedo cools the surface; it warms it.