The greenhouse effect

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The greenhouse effect

• Greenhouse effect. Warming of the lower layers of
  the atmosphere due to the fact that solar
  radiation, of relatively short wavelength,
  penetrates the atmosphere without appreciable
  absorption, and is, in large measure, absorbed
  only at the earth's surface while terrestrial
  radiation, of large wavelength, is absorbed by
  the atmosphere to a much greater extent (WMO).
  The phenomenon is named by analogy with a
  greenhouse, whose glass is much more transparent
  to short-wave solar radiation than to the
  longer-wave radiation from the interior of the
  greenhouse. Fears have been expressed that an
  increase in the concentration of carbon dioxide
  in the atmosphere could lead to an enhancement of
  the greenhouse effect with a consequent rise in
  temperature.
• WHO Glossary on air pollution 1980

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La Mer de Glace, Mont Blanc
Aletsch Bern Alps
1916 2001
1900 2001
www.gletscherarchiv.de
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The greenhouse effect

• Topics of concern
• Radiation
• Effective temperature of the Earth
• Radiation absorbtion
• Radiative forcing
• Water vapour and cloud feedback
• Optical depth

Natural greenhouse effect
Additional anthropogenic greenhouse effect
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The greenhouse effect

• References
• Barry RG, Chorley RJ (1998) Atmosphere, weather
  climate 3941
• Graedel TE, Crutzen PJ (1994) Chemie der
  Atmosphäre pp. 413428
• Jacob DJ (1999) Introduction to atmospheric
  chemistry pp. 113143
• Seinfeld JH, Pandis SN (1998) Atmospheric
  chemistry and physics pp. 10751112

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Greenhouse gas emissions as of 18th century
from Jacob (1999) fig. 7.1
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Global surface T trends
a
at northern mid-latitudes, taken from various
proxies (a instrumental data b historical
information c pollen data and alpine glaciers
d marine plankton and beach terraces). Time
sequence from current to past 150,000 years
b
Webb III et al., cited in Graedel and Crutzen
(1994) fig. 10.15
c
d
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Greenhouse effect natural processes

• Planet Earth an open physical system, in
  thermal equilibrium with its cosmic environment
• Energy ¹ Temperature
• Absorption of gases, absorption bands
• Most important sorbent ozone (absorbance of
  radiation lt 300 nm UV-radiation)
• Stratospheric T result of O3 re-radiance
• Terrestrial heat emission hindrance water
  vapour (62), CO2 (22), O3 (7), N2O (4), CH4
  (4)
• Sum total natural greenhouse effect
• Clouds
• high (Cirrus) absorption of IR-radiation gt
  reflection of short-wave radiation heating
  effect for Earth atmosphere
• low (Stratus) reflection gt absorption cooling
  effect

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Terrestrial energy balance
(ozone)
(CO2)
100 342 W m-2 or 11 x 109 J m-2 yr-1 incoming
solar radiation solar constant pr2 solar
constant 4pr2. Solid lines energy gains hatched
lines energy losses. Lu Earths black body
radiation Ld reradiated energy LE latent heat
transfer H sensible heat transfer
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Solar and terrestrial radiation spectra

• Double logarithmic plot! linear inset
• Black body radiation top of atmosphere
• Solar constant solar short-wave radiation with
  avg. flux density 1370 W m-2 available for
  planet Earth on surface 342 W m-2
• Atmospheric windows (8.513 µm see infrared)
  heat escapes from Earth
• Barry Chorley (1998) after Sellers 1965

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Radiation absorption in the atmosphere
Fleagle Businger 1963, and Möller 1973, in
Häckel H (1999) 4.ed.
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Terrestrial radiation spectrum at noon
Niger valley, Northern Africa
Hanel et al. 1972 , in Jacob (1999) Fig. 7-8
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Terrestrial radiation spectrum at noon
after Hanel et al. 1972 , in Jacob (1999) Fig.
7-8
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Terrestrial radiation spectrum at noon
An increase of ozone above about 30 km absorbs
relatively more incoming short-wave radiation,
causing a net decrease of surface
temperatures An increase of ozone below about 25
km absorbs relatively more outgoing long-wave
radiation, causing a net increase of surface
temperatures
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Global air temperatures (C) 19591989
Troposphere (1,59 km height) 0.1 to 0.3 C per
10 yrs
Stratosphere (1620 km height) -0.2 to -0.4 C
per 10 yrs for N-hemisphere -0.4 to -0.6 C per
10 yrs for S-hemisphere
from Hupfer Schönwiese (1998)
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Greenhouse effect global warming
Additional emissions of CO2 (50), CFCs (22),
CH4 (13), O3 (7), N2O (5), and H2O (3)
additional terrestrial heat emission hindrance
(relative effect) Results Tropospheric warming
(Earth surface and lower troposphere) Stratospheri
c cooling because of decreasing O3 and retained
long-wave radiation in the troposphere Heating of
lower troposphere, cooling of stratosphere
decreasing thermal stability of the atmosphere
More extreme weather patterns, storms,
etc. Warming of ocean water melting of
glaciers rise of sea-level Weakening of global
marine conveyor belt disturbance of gulf-stream
cooling in Europe (Rahmsdorf 1995)
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Greenhouse effect global warming
GWP for several gases Initial state for CO2 is
275 ppmv (pre-industrial level) for all others
is 0. Triangles show conc. in 1990 Data from
Houghton et al. 1990 (IPCC)
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Greenhouse gases and air temperature GWP
GWP
Heating function Xi(T) integration of radiative
forcing over time t RFi radiative forcing of gas
i ti atmospheric lifetime of i (exp decrease)
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Global air temperatures (C) 18601990
Combined land, air, and sea-surface T Relative to
19511980 average T
Seinfeld Pandis 1998) fig. 21.1, 21.2
Estimated air T variations various records,
mainly from Europe and eastern North America
relative to value for 1900 AD.
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Air temperature changes

• IPCC graph
• combination of 2 m above ground air temperatures
  and sea surface temperatures (Houghton et al.
  1996)
• 20th Century end of little ice age
• current increasing trend is statistically
  significant (scatter also increases)
• Temperature change is not homogenous
• Changes are similar on each hemisphere
• Extremes change differently with time
• since 1950, daily minima increase with double
  speed compared with maxima
• strong seasonal and regional differences
• the resulting decrease of inter-diurnal change
  corresponds with cloud cover increase (Houghton
  et al. 1996)

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Global precipitation trends

• Observations
• larger errors as compared with T measurements
• much smaller regional representativity
• hardly any data for oceanic realm
• very difficult assessment
• Interpretation
• increase of P and evaporation with increasing T
• acceleration of hydrologic cycle
• global P increase 1 according to IPCC (1996)

from Hupfer Schönwiese (1998)
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Avg. radiation forcing of soot and sulfate
soot
anthropogenic sulfate
from Schulz M (1998)
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NO3, SO4, Cl-conc. in Colle Gnifetti ice (4450 m
a.s.l.)
Cl (mg L-1)
NO3 (mg L-1)
SO4 (mg L-1)
from Schulz M (1998)
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Feedback mechanisms in the climate system
Effect predictions limited by our limited
knowledge of feedback mechanisms Feedback
positive or negative? Ice-albedo feedback
increasing glacier melt reduced albedo
additional warming at higher latitudes Water
vapour-T-increase feedback increased water
evaporation increased T loop effect Chemical
feedback CH4-increase OH-decrease further
CH4-increase (loss of most efficient atmospheric
cleaning mechanism) Cloud feedback increased
evaporation increased cloud formation denser
clouds higher global albedo (problem of cloud
height) Biotic feedbacks higher surface T
higher soil respiration higher degassing
higher CO2 levels increased greenhouse effect
but higher CO2 levels higher plant growth
after Graedel Crutzen (1994)