Greenhouse

🎯 How This Word Works in UPSC Writing

In climate science, the effect by which atmospheric gases absorb outgoing longwave radiation and re-radiate it, warming the surface. The physics point that earns marks is the asymmetry of wavelength: incoming solar radiation is shortwave and passes largely unimpeded, while the Earth re-radiates at longer infrared wavelengths that greenhouse gases absorb, so the atmosphere is largely transparent to what arrives and partly opaque to what leaves. The effect is natural and essential, since without it the surface would be far too cold for life, and the anthropogenic problem is its enhancement rather than its existence, which is worth stating because the phrase is frequently used as though the effect itself were the harm. Gases differ in two properties that must be kept apart: global warming potential, the warming per unit mass relative to carbon dioxide over a stated horizon, and atmospheric lifetime. Methane has a far higher potential but a short life, so cutting it yields rapid benefit, while carbon dioxide is weaker per tonne yet persists for centuries and therefore governs the long run.