IB›IB Physics HL›Mind mapsB.2 Greenhouse effectIB Physics HL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsEnergy balanceAbsorbed power equals radiated powerSolar constant about 1361 W/m²Intercepts πR2\pi R^2πR2, radiates 4πR24\pi R^24πR2Mean incoming intensity is S/4Albedo, emissivityAlbedo = scattered power ÷ incident powerEarth's mean albedo about 0.3Clouds, ice and snow reflect stronglye=power per areaσT4e = \frac{\text{power per area}}{\sigma T^4}e=σT4power per areaEquilibrium: (1−α)S4=eσT4(1-\alpha)\frac{S}{4} = e\sigma T^4(1−α)4S=eσT4Greenhouse gasesCH₄, H₂O, CO₂ and N₂OCO₂: fossil fuels, deforestationCH₄: livestock, rice paddies, landfillN₂O: nitrogen fertilisersWater vapour effect is mainly indirectGreenhouseeffect and energy balanceS/4α\alphaαeHow they absorbSun's radiation peaks in the visibleEarth emits infrared, peak about 10 μmVibrational levels match infrared photonsBonds resonate at infrared frequenciesRe-emission in all directionsEnhanced effectCO₂ up from 280 to over 420 ppmEffective emissivity falls, temperature risesMelting ice lowers albedoWarmer air holds more water vapourWithout effect: 255 K not 288 KExam tipsDivide S by 4, not 2Model limits: averaging, feedbacks, ocean time lag