Transcript Earth`s Climate - Atmospheric and Oceanic Sciences

Lecture 3a:
Radiation in the Atmosphere
and Climate
(Chapter 2)
Solar constant and solar radiation
Radiation processes
in the atmosphere
Wave spectrum
Short wave
Long wave
Climate Forcing
The ultimate driving force on the earth: the sun
Solar constant is the average solar radiation that reaches the earth on a
perpendicular plane to the sun ray (total area R2): S0=1368 W/m2
.
Short wave radiation (solar radiation) is normally the average solar radiation
on the surface of the spherical earth (total area 4R2): S= S0/4=342 W/m2
Long wave radiation (terrestrial radiation) is the back radiation to the space
by the earth with an effective temperature T as Q=T4 , where =5.67
10-8 W/m2K4 is the Stefan-Boltzman constant.
Blackbody radiation
A blackbody at temperature (in K) radiates energy at different wave length  as
C1
E( )  5
,
 [exp(C2 / T) 1]
where C  3.74 108W m 2 m 4 ,C  1.44 10 4 mK
1
2
are constants. The radiation has a maximum value at the wavelength
where a=2897 m K.
max=a/T,
Integrated in all the wavelength, we have the radiation energy flux as
E=T4
Why tropics is warmer than the poles?
Latitudinal
distribution
Latitudinal distribution
pole-equator contrast, implication for circulation
Why summer is warmer than winter?
Four seasons
Why climate is different in different regions:
Continental vs Marine Climate
Annual temperature range
Land – sea contrast
Thermal inertial
Why the Earth surface temperature
is about 15oC (288K)?
Climate modeling
Global Mean (0-Dimension) climate model
• Radiative equilibrium climate models
(Lecture 3: Note. A)
Radiative Equilibrium Model
S
T4
Total heat flux across the surface = S -  T4 =0
T c= (S/ )1/4 , S=342 Wm2  T c =279oK=6oC,
Too cold!
,
Cloud Albedo Effect: Radiative Equilibrium Model
S
S
Cloud
(1-)S
T4
Total heat flux across the surface = (1-a)S -  T4 =0
T cc= [(1-a)S/ ]1/4 ,  T cc =255oK= -18oC
Even colder
Greenhouse Effect (H2O!)
(1-)S
Tg4
(1-)S
glass
T4
Heat fluxes:
surface = (1-a)S +  Tg4 -  T4 =0
Top
= (1-a)S -  Tg4 = 0
(or radiation balance for the glass layer: 2 Tg4 =  T4 )
Tg= ((1-a)S/ )1/4 = Tcc=255K ,  Tcg =21/4Tg=288oK=15oC
About right…
How does the climate respond to
global warming forcing?
CO2 induced Radiative Forcing
Climate Sensitivity
CO2 induced Radiative Forcing
RF= 5.25 ln (CO2) W/m2
(S. Arrhenius, 1900)
Examples: Present relative to 1850 (CO2 =250ppm)
RF=5.25 *ln (385 / 250 ppm) = ~2.5 W/m2
Doubliing CO2
RF=5.25 *ln (500 / 250 ppm) = ~4 W/m2
Climate Sensitivity
ΔT=b*RF
b = climate sensitivity!
= increase in temperature per unit increase
in radiative forcing
Svante Arrhenius
Born
19 February 1859(1859-02-19)
Vik, Sweden
Died
2 October 1927(1927-10-02)
(aged 68)
Stockholm, Sweden
Nationality
Swedish
Fields
Physics, chemistry
Institutions
Royal Institute of Technology
Alma mater
Uppsala University
Stockholm University
Doctoral advisor
Per Teodor Cleve, Erik Edlund
Doctoral students
Oskar Benjamin Klein
Known for
Arrhenius equation
Theory of ionic dissociation
Acid-base theory
Notable awards
Nobel Prize for Chemistry (1903)
Franklin Medal (1920
Global Warming Response
Radiative Equilibrium Model
RF(CO2)
S
Global warming prediction:
Total flux = S +RF-  T4 =0
b
T = [(S+RF)/ ]1/4 ~= (S/ )1/4 +b*RF = Tc +b*RF,
or global warming
Climate sensitivity:

Double CO2 :
RF
T4
here RF<<S
ΔT= T- Tc = b*RF
b=d (S/ )1/4 /dS = 1/(4 Tc 3)=0.2 K / Wm-2
ΔT = b*RF = 0.2 * 4 = 0.8oK,
small??
Cloud Albedo Effect: Radiative Equilibrium Model
S
S
RF
Cloud
(1-)S
T4
Total heat flux across the surface = (1-a)S +RF-  T4 =0
T cc= [(1-a)S/ ]1/4 ,  T cc =255oK= -18oC
Climate sensitivity:
Double CO2 :
b=1/(4 Tcc 3)=0.37 K / Wm-2
ΔT = b*RF = 0.37* 4
= 1.5oK
greater !
Greenhouse Effect (H2O!)
(1-)S
RF
Tg4
(1-)S
glass
T4
Heat fluxes:
surface = (1-a)S + RF- Tg4 -  T4 =0
Top
= (1-a)S + RF- Tg4 = 0
T cg= [2(1-a)S/ ]1/4 =288oK=15oC
Now climate sensitivity: ,
b=1/(4 Tcg 3)=0.45 K / Wm-2
Double CO2 :
ΔT = b*RF = 0.45* 4
= 1.8 ~ 2oK, even greater !
Svante Arrhenius
To explain the ice age, Arrhenius
estimated that halving of CO2 would
decrease temperatures by 4 - 5 °C
(Celsius) and a doubling of CO2 would
cause a temperature rise of 5 - 6 °C. In his
1906 publication, Arrhenius adjusted the
value downwards to 1.6 °C (including
water vapour feedback: 2.1 °C). Recent
(2007) estimates from IPCC say this value
(the Climate sensitivity) is likely to be
between 2 and 4.5 °C. Arrhenius
expected CO2 doubling to take about 3000
years; it is now estimated in most
scenarios to take about a century.
Lecture 3b: Heat Transfer
in the Atmosphere
(Chapter 2)
Convection,
Stratification
Latitudinal Differential Heating--
The driving force for circulation
Atmospheric General Circulation
Rotation
Coriolis force
Monsoon,
precipitation
monsoons
Subtropical High
H
Geostrophic
flow
Surface temperature, Clouds
Extratropical
cyclones
Tropical
convection
Extratropical
cyclones
Infrared Images
Extratropical
cyclones
Tropical
convection
Extratropical
cyclones
Water vapor content
Extratropical Cyclone, Storm Track
Visible light
Infrared
(short wave)
(long wave)
Water vapor
Regional climate
Regional topographic effect
Vertical structure of the atmosphere
Vertical mass distribution
Stratosphere
Troposphere
The Role of Water: Fuel for the Climate Heat Engine
Hydrological Cycle
Latent heat of melting and vaporization
Water vapor content
Lecture 3c: Heat Transfer
in the Ocean
(Chapter 2)
Ocean Circulation, Ocean Gyres
How does wind drives the ocean?
Ekman flow
Ekman spiral
Ekman layer
Ocean gyres
Vertical temperature
structure
Thermocline
Wind-driven Upwelling
Overturning
circulation
Thermohaline circulation
Thermo--haline circulation
Equator
North Pole
Equator
North Pole
Saline
Fresh
Warm
Cold
Haline circulation
Thermal circulation
Thermo-Haline circulation
The Coupled Climate System
Stationary Waves
Hadley Cell
Transient
Eddies
S. Pole
N. Pole
EQ
Thermocline circulation ~
decadal
N. Atlantic THC ~ decadalcentennial
Southern Ocean THC ~ millennial
Schematic figure of various branches of climatic teleconnections in the atmosphere and ocean. The atmospheric
teleconnections occur at fast time scales, usually shorter than monthly to seasonal (not marked). The oceanic teleconnection
occurs at a wide range of time scales as marked.
Lecture 3d: Climate Modeling
(Chapter 2)
Climate Modeling
• General Circulation Model
• Energy Balance Model
(L3: Note.B)
TRACE-21: Experiment Set Up
CCSM3 (T31_gx3v5) + Dyn Veg
Atmosphere (CAMT31):
3.75o x 3.75o x 26 level
Ocean (POP+Sea Ice)
3’ to 0.5o on equator
Land (CLM+LPJ):
Atmosphere
3.8°
Forcing:
realistic orbital, GHGs,
continental ice sheet (ICE-5G, each 500-yr)
land sea mask (twice)
Sea Ice
x3°
Ocean
Land
x3°
3.8°
Meltwater : No. 1 uncertainty!
22ka
H1
BA
0ka
YD
A Pine Tree
Earth System Model
Biogeochemical Cycle
(e.g. Carbon cycle)
Test Climate Model:
Climate Sensitivity
• From last glacial era, we know this is
roughly 5 C per 7 W/m2
– glacial to post-glacial
– This amounts to ~ 0.75 C / W m-2
– IPCC says for doubling of CO2, should
expect 1-6 C of warming
LGM Climate
CLIMAP SST
Model SST
Model Tair
1) CO2 vs. ice sheet
2) Proxy uncertainty vs.
model uncertainty
Liu et al., 2002, GRL
The End
Lecture 3