Higher Tier: The Greenhouse Effect in Detail

The greenhouse effect works as follows: short-wave radiation from the Sun passes through the atmosphere and warms Earth's surface. The warmed surface re-emits this energy as longer-wave infrared radiation (heat). Greenhouse gases — including CO₂, methane, water vapour, and nitrous oxide — absorb this infrared radiation and re-emit it in all directions, including back towards Earth. This traps heat in the lower atmosphere, raising surface temperatures beyond what they would be naturally.

Without any greenhouse effect, Earth's average temperature would be around −18°C rather than the current +15°C — the natural greenhouse effect is essential for life. The problem is the enhanced greenhouse effect: human activities have increased greenhouse gas concentrations far above natural levels (CO₂ from 280 ppm pre-industrial to over 420 ppm today), amplifying the effect and causing global warming.

Methane is around 25 times more potent as a greenhouse gas than CO₂ over a 100-year period. It is produced by cattle ranching, rice paddies, landfill, and natural decomposition in wetlands. Deforestation for cattle ranching therefore contributes in two ways: releasing CO₂ from trees AND increasing methane from livestock.