BST 200 Radia+ve forcing and Greenhouse Gases

Transcription

1 BST 200 Radia+ve forcing and Greenhouse Gases

2 Atmospheric Burden and Residence Time suppose a tub holds 100 kg of water (Burden) and Source = Sink = 5 kg/minute Residence +me = 100 kg 5 kg/minute = 20 minutes

3 The Terrestrial Organic Carbon Cycle Photosynthesis Atm. CO Gt RespiraHon Plants Consumers 600 Gt 0 death 30 decay 30 Soils and sediments 1,600 Gt 0.05 burial Sedimentary Rocks 10,000,000 Gt death 0 oxidahon 0.05

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5 Global CO 2 budget for (blue) and (red) (GtC per year) to 2000: = to 2008: = 4.1

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7 using: A = 0.3; S = 1370 W/m2; σ = W/m2/K4 T = 255 K = - 18 C = 0 F = Effec+ve Temperature = T E

8 T s With the new fluxes, the ground temperature, T s, must be warmer than effec+ve temperature T s = 288 K = 15 C = 60 C

9 Greenhouse effect The greenhouse effect is the difference between the effechve temperature and actual temperature: ΔT G = T S - T E = 15 C (- 18 C) = 33 C = 60 F It depends on: Atmospheric composihon greenhouse gases Amount of atmosphere Albedo of planet (surface + atmosphere) Clouds Aerosol dust

10 Sister Planets

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12 Solar radiahon distribuhon

13 Most radiahon emi^ed by the surface is absorbed by the atmosphere Emission from ground = 288 K

14 Incoming solar and outgoing terrestrial radiahon Percent absorbed

15 Natural and anthropogenic contribu+on to the Greenhouse Effect Source: Jacobson 2002

16 Climate Forcing Changing the Greenhouse Effect Source: IPCC Slide 16

17 Aerosol Effects on Climate! Los Angeles Smog ( Alan Clements)"

18 Aerosol effects on climate Mul+ple effects, complex problem An aerosol is a solid or liquid par+cle suspended in air 1. Direct sca^ering of light back to space: cooling effect. 2. Direct absorphon of light by black aerosols (soot): warming effect. 3. Increase in ophcal thickness of clouds: cooling effect. 4. Darkening of snow or ice by aerosols: warming effect. Slide 18

19 Aerosol Effects on Climate! Clockwise from top leb: LA smog, African dust, dust on a European glacier, ship tracks and smoke off Calif coast.

20 Greenhouse gases

21 Why does water vapor vary so much? Pressure force exerted by the total number of molecules Vapor pressure force exerted by a single kind of molecule (pressure = sum of vapor pressures) Vapor pressure of water force exerted by water vapor in a parcel of air

22 Why does water vapor vary so much? SaturaHon amount of H 2 O vapor in air at point of condensahon (maximum amount of vapor air can hold ) SaturaHon vapor pressure increases exponenhally with T Warmer air has a LOT more water vapor than cooler air ArcHc: T ~ 0 C (273 K) Tropics: T ~ 30 C (303 K)

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24 How do clouds form? Start with air parcel containing water vapor Lib parcel up HeaHng at surface Upslope wind forced by mountains Convergence of mass by large scale circulahon Parcel cools by rising Parcels cool because they do work by expanding as they rise due to pressure differences Parcel temperature reaches saturahon vapor pressure CondensaHon occurs => cloud forms

25 Parcel with condensed water P1, T1 P1 < P0 (pressure decreases with al+tude) T1 < T0 (parcel does work by expanding) T1 < T[satura+on] => condensa+on occurs Parcel with H2O vapor P0, T0

26 Parcel SaturaHon SaturaHon amount of H 2 O vapor in air at point of condensahon Parcel starts at T0 Cools to T1 (by libing) Reaches saturahon curve T1 T0

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29 Stratus deck (low cloud)

30 Cirrus cloud deck high clouds

31 How do we know what clouds look like (on the inside)? Millimeter cloud radar (MMCR) at the Atmospheric Radia+on Measurement site near Ponca City, OK Wavelength = 8 mm (about 1/3 of an inch Dish size = 3 meters (Rain radars have wavelength of 3 to 10 cm)

32 Mix of Clouds 24 hour +me series Data acquired with a ver+cally poin+ng millimeter wavelength radar in Oklahoma

33 Clouds from Space Arkansas area

34 Clouds 1. Reflect solar radia+on => cools planet 2. Absorb and emit infrared radia+on => warms planet Parcel with condensed water P1, T1 Parcel with H2O vapor P0, T0

35 Total solar down Downwelling Solar Radia+on April 6, 2005 Cloudy day (Oklahoma ARM site) April 7, 2005 Clear day (Oklahoma ARM site)

36 Downwelling Infrared Radia+on IR signal (ignore other curves) April 6, 2005 Cloudy day (Oklahoma ARM site) Clouds move out, IR goes down April 7, 2005 Clear day (Oklahoma ARM site)

37 Low Clouds High Clouds

38 Earth radiahon budget experiment Measurements of SW and LW fluxes at top of atmosphere Plots available at h^p://itg1.meteor.wisc.edu/wxwise/museum/a2main.html

39 ERBE: SW albedo SummerHme Stratus

40 ERBE: LW emission SummerHme

41 ERBE: Net RadiaHon SummerHme

42 ERBE: Cloud forcing Global map of the effect of clouds on the top of atmosphere radiahon budget ΔF = Flux with clouds Flux without clouds = ΔF(SW) + ΔF(LW) ΔF(SW) < 0 (clouds reflect) ΔF(LW) > 0 (clouds trap heat) If ΔF < 0, then ΔF(SW) > ΔF(LW) If ΔF > 0, then ΔF(SW) < ΔF(LW)

43 ERBE: Cloud forcing ΔF(LW) > 0 PosiHve everywhere: Clouds reduce IR emissions ΔF(SW) < 0 NegaHve (almost) everywhere: Clouds reflect sunlight

44 ERBE: Cloud forcing Add them together: If ΔF < 0, then ΔF(SW) > ΔF(LW) If ΔF > 0, then ΔF(SW) < ΔF(LW)

45 Cloud Forcing What is the sign for current climate? NegaHve => clouds cool planet PosiHve => clouds warm planet Answer: Clouds cool the planet SW forcing is larger (in absolute sense) than LW forcing