1 / 26

TOPIC III THE GREENHOUSE EFFECT

TOPIC III THE GREENHOUSE EFFECT. SOLAR IRRADIANCE SPECTRA. 1  m = 1000 nm = 10 -6 m. Note: 1 W = 1 J s -1. TOTAL SOLAR RADIATION RECEIVED BY EARTH. Solar constant for earth: 1368 W m -2. Solar radiation received outside atmosphere per unit area of sphere

tcarranza
Télécharger la présentation

TOPIC III THE GREENHOUSE EFFECT

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. TOPIC IIITHE GREENHOUSE EFFECT

  2. SOLAR IRRADIANCE SPECTRA 1 m = 1000 nm = 10-6 m • Note: 1 W = 1 J s-1

  3. TOTAL SOLAR RADIATION RECEIVED BY EARTH • Solar constant for earth: 1368 W m-2 • Solar radiation received outside atmosphere • per unit area of sphere • = (1370) x ( re2)/(4  re2) = 342 W m-2

  4. EFFECTIVE TEMPERATURE OF EARTH • Effective temperature of earth (Te) • Temperature detected from space • Albedo of surface+atmosphere ~ 0.3 • 30% of incoming solar energy is reflected by clouds, ice, etc. • Energy absorbed by surface+atmosphere = 1-0.3 = 0.7 • 70% of 342 W m-2 = 239.4 W m-2 • Balanced by energy emitted by surface+atmosphere • Stefan-Boltzman law: Energy emitted =  Te4 •  = 5.67 x 10-8 W m-2 K-4 • Solve  Te4 = 239.4 • Te = 255 K

  5. GLOBAL TEMPERATURE • Annual and global average temperature ~ 15 C, i.e. 288 K • Te = 255 K --> not representative of surface temp. of earth • Te is the effective temp. of the earth + atmosphere system • that would be detected by an observer in space

  6. ENERGY TRANSITIONS • Gas molecules absorb radiation by increasing internal energy • Internal energy  electronic, vibrational, & rotational states • Energy requirements • Electronic transitions •  UV (< 0.4 m) • Vibrational transitions •  Near-IR (< 0.7-20 m) • Rotational transitions •  Far-IR (> 20 m) • Little absorption in visible range (0.4-0.7 m) • Gap between electronic and vibrational transitions • Greenhouse gases absorb in the range 5-50 m • Vibrational and rotational transitions

  7. GREENHOUSE GASES • Vibrational transitions must change dipole moment of molecule • Important greenhouse gases • H2O, CO2, CH4, N2O, O3, CFCs • Non-greenhouse gases • N2, O2, H2, Noble gases

  8. ATMOSPHERIC ABSORPTION OF RADIATION • ~100% absorption of UV • Electronic transitions of • O2 and O3 • Weak absorption of visible • Gap in electronic and • vibrational transition energies • Efficient absorption of terrestrial radiation • Greenhouse gas absorption • Important role of H2O • Atmospheric window between 8 and 13 m

  9. A SIMPLE GREENHOUSE MODEL 239.4 W m-2 (1-f) To4 f T14 absorbed = f  To4 f T14  To4 • Incoming solar radiation = 70% of 342 W m-2 = 239.4 W m-2 • IR flux from surface =  To4 • Assume atmospheric layer has an absorption efficiency = f • Kirchhoff’s law: efficiency of abs. = efficiency of emission • IR flux from atmospheric layer = f  T14 (up and down)

  10. RADIATION BALANCE EQUATIONS 239.4 W m-2 (1-f) To4 f T14 absorbed = f  To4 f T14  To4 • Balance at top of atmosphere • f  T14 + (1-f)  To4 = 239.4 • Balance for atmospheric layer • f  T14+f  T14 = f  To4

  11. THE GREENHOUSE EFFECT 239.4 W m-2 (1-f) To4 f T14 f T14 absorbed = f  To4  To4 • To = 288 K • f = 0.77; T1 = 241 K • Greenhouse gases  gases that affect f • As f increases, To and T1 increase

  12. THE IPCC THIRD ASSESSMENT

  13. CONCEPT OF RADIATIVE FORCING 239.4 W m-2 (1-f) To4 f T14 absorbed = f  To4 f T14  To4 • Consider increase in concentration of a greenhouse gases • If nothing else changes •  f increases outgoing terrestrial radiation decreases • Change in outgoing terrestrial radiation = radiative forcing

  14. RADIATIVE FORCING AND TEMPERATURE CHANGE 239.4 W m-2 (1-f) To4 f T14 absorbed = f  To4 f T14  To4 • Response to imbalance • To and T1 increase  may cause other greenhouse gases to • change  f  (positive feedback) or  (negative feedback) • To and T1 may  or  f  T  …  Rad. balance • Radiative forcing is measure of initial change in • outgoing flux

  15. RADIATIVE FORCING • Permits assessment of potential climate effects of • different gases • Radiative forcing of a gas depends not only on change in • concentration, but also what wavelengths it absorbs • Aerosols can exert a negative radiative effect (i.e. have a • cooling effect) by reflecting radiation (direct effect) and • by increasing reflectivity of clouds (indirect effect)

  16. GLOBAL WARMING POTENTIAL • Index used to quant. • compare radiative forcings • of various gases • Takes into account lifetimes, • saturation of absorption

  17. FORCINGS AND SURFACE TEMPERATURE • Climate sensitvity parameter (): To =  F • Global climate models   = 0.3-1.4 K m2 W-1

  18. THE TEMPERATURE RECORD

  19. RECENT CHANGES IN SURFACE TEMPERATURE • Trend differences due to • differences in spatial av., • diff. in sea-surface temps., • and handling of urbanization • Same basic trend over last • 100 years • Increase in T by 0.6-0.7 C

  20. POTENTIAL CAUSES OF TEMPERATURE CHANGES 239.4 W m-2 absorbed = f  To4 • Variations in solar radiation at top of atmosphere • Changes in albedo (e.g. due to changes in cloud cover) • Changes in greenhouse gas forcing (i.e., change in f)

  21. SOLAR VARIABILITY • Changes in sunspots and surface conditions

  22. CHANGES IN CLOUD COVER • Incoming solar radiation = 0.7 x 342 W m-2 = 239.4 W m-2 • Consider albedo change of 2.5% • Albedo = 0.3 x 1.025 = 0.3075 • Incoming solar radiation = 0.6925 x 342 W m-2 = 236.8 W m-2 • Radiative forcing =236.8 – 239.4 = - 2.6 W m-2 •  Comparable but opposite to greenhouse gas forcing • Clouds are also efficient absorbers of terrestrial radiation •  Positive forcing • Cloud effects are larege source of uncertainty in climate • projections

  23. MODEL SIMULATIONS OF RECENT PAST

  24. CLIMATE PROJECTIONS

  25. POTENTIAL IMPACTS

  26. JULY HEAT INDEX FOR S.E. U.S.

More Related