9.3 The Greenhouse Effect

does all incoming solar radiation reach earth’s surface?

no

• 26% reflected back into space by clouds and atmosphere

• 19% absorbed by atm. & clouds & radiated out into space & down to earth

• rest reaches earth’s surface - (can be absorbed/reflected depending on the albedo of the surface it strikes)

darker, lower albedo surfaces absorb sunlight and release what

• infrared radiation which is thermal radiation, which we feel as warmth

most important greenhouse gasses:

• carbon dioxide

• methane

• nitrous oxide

• CFCs/HCFCs/HFCs

• water vapor

greenhouse effect

• gasses in earth’s atmosphere trap heat from the sun & radiate it back down to earth

what would happen without the greenhouse effect?

• earth would be too cold to support life

how does the greenhouse effect work?

• solar radiation (light waves like UV & visible light) strike earth’s surface, heating it

• earth’s surface releases infrared radiation

• greenhouse gases absorb infrared radiation & radiate it both out into space and back toward earth

• portion coming back to earth is the greenhouse effect

global warming potential (GWP)

• measure of how much a given molecule of gas can contribute to the warming of the atmosphere over a 100 year period, relative to co2

what 2 factors is GWP based on?

• residence time - how long a molecule stays in the atmosphere

• infrared absorption - how well the gas absorbs & radiates infrared radiation

what GWP does Co2 have

• GWP of 1 (all other gases are measured in relation to Co2)

what GWP does methane CH4 have

• remains in atmosphere around 12 years, absorbs more IR than Co2

what GWP does nitrous oxide have

• remains in atmosphere around 115 years

• absorbs much more IR than Co2