Introduction to Climate Change and Greenhouse Gases
Climate change is one of the most pressing environmental challenges of our time. At its core, it is driven by the enhanced greenhouse effect , the trapping of excess heat in Earth's atmosphere due to rising concentrations of greenhouse gases.
The primary greenhouse gases responsible are:
- Carbon dioxide (CO₂) , released mainly through fossil fuel combustion, deforestation, and industrial processes
- Water vapour (H₂O) , the most abundant greenhouse gas but not directly controlled by human activity
- Methane (CH₄) , released from livestock, rice paddies, landfills, and melting permafrost
- Nitrous oxide (N₂O) , produced by agricultural soils, livestock, and fertiliser use; distinct from NOₓ (NO and NO₂), which are air pollutants but not significant direct greenhouse gases in this context
The overall impact of any greenhouse gas depends on two key factors:
- Its ability to absorb long-wave (infrared) radiation
- Its concentration in the atmosphere
Methane is approximately 28–30 times more effective at trapping heat than CO₂ over a 100-year period (IPCC AR6, 2021) , but because its atmospheric concentration is far lower, CO₂ has a greater total warming effect overall. Over a 20-year period, methane's warming potential is even higher (~80×), making early reductions in methane emissions particularly impactful.
The Mechanism of the Greenhouse Effect
Understanding how greenhouse gases warm the planet is essential for this topic.
Step-by-step process:
- The Sun emits short-wave radiation (visible light and UV) that passes through the atmosphere relatively easily.
- Earth's surface absorbs this energy and warms up.
- The warmed surface re-emits energy as long-wave (infrared) radiation directed back towards space.
- Greenhouse gas molecules in the atmosphere absorb this outgoing infrared radiation.
- The absorbed energy is re-emitted in all directions, including back down towards Earth's surface.
- This traps heat within the lower atmosphere, warming the planet , the greenhouse effect.
Think of the atmosphere like the glass panels of a greenhouse. Sunlight passes through easily, warming the interior. The glass then prevents heat from escaping, keeping the inside warm even when it is cold outside. Greenhouse gases act like that glass, but on a planetary scale.
Do not confuse the enhanced greenhouse effect (caused by increasing greenhouse gas concentrations due to human activity) with the natural greenhouse effect (which has always existed and makes Earth habitable). The problem is the enhancement of this effect, not the effect itself.
