Greenhouse Effect. Julian Barber, Emma Brashear, Timothy Opdahl, Ezra Shepherd-Lykken, Roland Taracks

Transcription

1 Greenhouse Effect Julian Barber, Emma Brashear, Timothy Opdahl, Ezra Shepherd-Lykken, Roland Taracks

2 Intensity of the suns radiation on the planet Sun radiates at 3.9 x W. Earth's orbital radius is 1.5 x m Surface Area of a sphere = (4)(pi)(r 2 ) intensity = P / A intensity = (3.9 x ) / (4(pi)(1.5 x ) 2 ) = 1380 J/s per m 2

3 Albedo Definition: The proportion of the incident light or radiation reflected by a surface, typically that of a planet or moon. In Plain English: It's the reflectivity of an object, planet, etc. Scale is from 0 (lowest albedo)(coal has an albedo of 0.1) to 1 (highest albedo)(snow has an albedo of 0.9).

4 Factors determining a planet's albedo The earth's albedo constantly changes The biggest factor that affects the earth albedo is cloud coverage Clouds have an albedo of 0.9 Different terrain types have different effects on the Albedo For Example: Snow and ice reflect a lot of light Water reflect very little The earth's average albedo is 0.3

5 Causes of the greenhouse effect The earth receives electromagnetic radiation (mainly visible light) from the sun The earth releases some of the radiation back to the atmosphere as Infrared Radiation Some of the IR is captured by greenhouse gasses and turned into heat

6 Diagram of Greenhouse Effect

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8 The Greenhouse Gases There are a few main greenhouse gasses CH 4 (Methane) CO 2 (Carbon dioxide) N 2 O (Nitrous Oxide) H 2 0 (Water) There are many natural and manmade sources of greenhouse gasses.

9 Water Vapor (H2O) Main source: Natural water in the air

10 Carbon Dioxide (CO2) Sources: The main source of carbon dioxide is human activity namely the burning of coal, natural gases, and oil. There are also natural instances of CO 2 in the air.

11 Methane (CH4) Sources: The emission of methane into the atmosphere is split about between human activity and natural sources. The human activities include, fossil fuel production, animal husbandry (enteric fermentation in livestock and manure management), rice cultivation, biomass burning, and waste management. Natural sources include, wetlands, gas hydrates, permafrost, termites, oceans, freshwater bodies, non-wetland soils, and wildfires.

12 Nitrous Oxide (N2O) Sources: N 2 0 has very similar sources to CO 2. Some comes from human activities like engines (diesel) and power factories. Fun Fact: 1 pound of N 2 O has 300 times the impact on warming the environment than 1 pound of CO 2.

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15 How greenhouse gases work Greenhouse gasses work on the main principle of resonance. Infrared Radiation vibrates at a certain frequency

16 Resonance Greenhouse gases, like CO2, can vibrate at the same frequency as IR, thus absorbing it. Some greenhouse gasses can vibrate at a range of frequencies, picking up a range of IR.

17 Absorption of greenhouse gases Depending on the wavelength the amount of radiation absorbed changes. CO 2 and H 2 O absorb the most infrared radiation.

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19 The Nature of Black-Body Radiation A black-body is something that absorbs all energy and reflects none of it back Black-Body radiation is often used to confirm the Big Bang Theory By the laws of Thermodynamics a black body is a perfect emitter of radiation

20 Black Body Radiation Lampblack, Powdered Carbon, has less than 2% reflectivity and is the closest that has been found to an ideal Black Body.

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22 Stefan-Boltzmann law P=eoAT^4 P=Power radiated by a radiator per unit area (measured in Watts). o=stefan-boltzmann Constant=5.67 X 10^-8 Wm^-2K^-4 A=Surface area of the emitter (measured in meters^2) T=Temperature (measured in Kelvin) e= Emissivity of a material

23 Emissivity Emissivity is defined as the ratio of the radiant energy emitted by a surface to that emitted by a blackbody at the same temperature. Emissivity is dimensionless.

24 Comparing Emission Rates The more reflective a material it is, the lower its emissivity is. Materials that absorb radiation more readily have higher emissivities. A blackbody has an emissivity of 1 while a completely reflective surface would have an emissivity of 0. A mirror has an emissivity of 0.1 Coal has an emissivity of 0.9

25 Emission rate at 100 K of 1m 2 of... Cement=3.06W=(.54)o(1)100 4 Glass=5.22W=(.92)o(1)100 4 Ice=5.50W Paper: White=3.86W Skin=5.56W Stainless Steel=3W

26 Surface Heat Capacity Definition: The amount of heat required to change the temperature of an object's surface (expressed in Joules per Kelvin) C = Q / (A T)

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28 Problems on the Greenhouse Effect The average rate of incoming radiation is 364 joules per square metre per second. rate of incoming radiation = 364 Jm -2 s -1 The rate of outgoing radiation depends only on the temperature of the Earth, and is given by the Stefan-Boltzmann Law: rate of outgoing radiation = σt 4 where σ = 5.67 x 10-8 Js -1 m -2 K -4

29 Climate Problem #1 (incoming radiation intensity - outgoing radiation intensity) x time/surface heat capacity= change in temperature What is the annual outgoing radiation if the incoming radiation is 364Jm -2 s -1 and the change in temperature is 3K? There are seconds in a year, and the surface heat capacity of the earth is 4 x 10 8 JK -1 m -2 3K=((364-outgoing radiation) x )/(4 x 10 8 ) Outgoing radiation=-((3k x 4 x 10 8 )/ ) -364 =326Jm -2 s -1

30 Climate Problem #2 What would the annual temperature change be if the incoming radiation was 360Jm -2 s -1 and the outgoing radiation was 300Jm -2 s -1? The specific heat capacity of earth is 4 x 10 8 JK -1 m - 2. There are seconds in a year. T=(( ) x )/(4 x 10^8)=4.7K

31 Sources/links htm vid=3&sid=b3729a99-acf4-4bb8-8db2-43f2dfa63e38% 40sessionmgr13&hid=9&bdata=JnNpdGU9c3JjLWxpdmU% 3d#db=ulh&AN= html pdf pdfhttp://