EAS 48800/B8800/SUS7300 Climate & Climate Change
Instructor: Prof. Johnny Luo,
Time: M/W 2:00-3:15pm; Location: MR044;
Get syllabus from class website:
http://www.sci.ccny.cuny.edu/~luo/EAS488
What does “climate science” study?
If the question was asked 60 yrs ago, the answer would be long-term
averages of surface meteorological conditions (e.g., temperature and
precipitation). Climatologists talked about “climate zones”.
Back then,
climatology was a
highly descriptive
field of study.
This is NOT what
this class
emphasizes.
Climate Science (1900 – now)
(Stage 1) At the beginning of 1900s, climate science or
climatology concerns long-term averages of the surface
meteorological conditions (e.g., temperature and precipitation).
(Stage 2) By 1950s, meteorology has extended the scope to
also include the upper air. Accordingly, climatology has
evolved into long-term statistics of the whole atmosphere. In
today’s terminology, we call it “atmospheric general
circulation”.
(Stage 3) Since 1980s, the concept of Climate System has
been gradually established, which includes not just the
atmosphere, but also ocean, land surface, etc. The scope of
Climate Science is now much broader.
Research tools have also been revolutionized.
Two important research tools for today’s Climate Science
Earth observations
2hc 2
Bλ (T) = 5
λ
€
1
e
hc
kλT
−1
Climate & Climate Change
Climate & Climate Change
Introduction to the Climate System
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
Definition & scope of the climate system
Atmospheric temperature
Atmospheric composition
Atmospheric pressure
Atmospheric humidity
Ocean
Cryosphere
Land surface
Major components of the climate system
Cryosphere: good reflector
of sunlight; holds a lot of
frozen water
Atmosphere: not very
“visible” except in presence
of clouds.
Ocean: covers ~ 70% of
the Earth. Huge reservoir
of water. Affects weather
and regulates climate.
Land surface: ~ 30% of
the Earth. Our primary
dwelling place.
Introduction to the Climate System
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
Definition & scope of the climate system
Atmospheric temperature
Atmospheric composition
Atmospheric pressure
Atmospheric humidity
Ocean
Cryosphere
Land surface
Atmospheric Temperature
Quick fact: Global average temperature near the surface: 288 K
or 15 0C or 59 0F.
A number of ways to understand
atmospheric temperature:
1. 
Global average surface
temperature (0D);
2. 
Vertical structure (1 D);
3. 
Geographical distribution of
surface temperature (2D);
4. 
Latitude-height cross section
(2D)
Most of this class
focuses on this part of
the atmosphere.
Atmospheric temperature lapse rate: Γ≡ - ∂T/ ∂z.
For the lowest 10-15 km (troposphere), the lapse rate is
almost always positive, meaning temperature decreases with
height.
Global mean tropospheric lapse rate is ~ 6.5 0C/km. But it
changes with altitude, season and latitude.
An important feature: tropopause
Geographical distribution of surface temperature
Jan
Jul
1. 
Global average
surface temperature
(0D);
2. 
Vertical structure (1
D);
3. 
Geographical
distribution of surface
temperature (2D);
4. 
Latitude-height cross
section (2D)
Annual range
of surface
temperature
This is what we
call zonal mean
Think-Pair-Share:
What accounts for the
land-ocean differences?
Outline
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
Definition & scope of the climate system
Atmospheric temperature
Atmospheric composition
Atmospheric pressure
Atmospheric humidity
Ocean
Cryosphere
Land surface
Composition of the atmosphere
Gas
Volume
-------------------------------------------------------------N2
78.1%
O2
20.9%
Ar
0.9%
CO2
0.0365%
Methane
0.00017%
Ozone (O3)
0.000004%
CFC
0.00000002%
Water vapor
variable (0 - 4%)
How did the Earth get today’s composition of the atmosphere?
Ocean, glaciers,
lakes and rivers
Water vapor (H2O)
Oxygen (O2)
Carbon Dioxide (CO2)
Nitrogen (N2)
Chemically stable so N2 stays.
Altitude, Km
Atmosphere composition as a function of altitude
O2
N2
H 2O
Goody 1995
Outline
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
Definition & scope of the climate system
Atmospheric temperature
Atmospheric composition
Atmospheric pressure
Atmospheric humidity
Ocean
Cryosphere
Land surface
Pressure decreases monotonically
with height
The lowest 15 km of the
atmosphere contains
90% of the atmospheric
mass.
Pressure = weight / area
1 Pascal = 1 N/m2
Earth’s surface pressure
≈ 100,000 Pascal (1 bar)
1 mb=1/1000 bar
1000 mb = 1 bar
Sometimes, we use hPa,
where 1hPa = 100 Pascal
Change of pressure with height:
Hydrostatic Equation
dp = −ρgdz
p = ρRT
(Equation of state)
p
gdz
RT
dp
g
=−
dz
p
RT
ΔP = P1 - P2
€
= - density x gravity x ΔZ
dp = −
P2
p = p0e−z / H ,where H ≡
ΔP=P1-P2
ΔZ
€
P1
gravity
RT
g
H is called scale height;
~ 7600 m for the Earth’s
atmosphere.
Implication of the hydrostatic equation
p = p0e
€
−z / H
RT
,where H ≡
≈ 8 km
g
1.  Atmospheric pressure decreases exponentially (every
8 km, pressure “e-folded”, i.e., becoming e-1 or 1/3 of
its original value):
At 8 km, p=1/3 p0;
at 16 km, p=1/9 p0;
at 24 km, p=1/27 p0
2.  Scale height H is a function of temperature: for
warmer air column, pressure decreases more slowly
with height.
Implication of the hydrostatic equation
p = p0e
−z / H
RT
,where H ≡
g
Scale height H is a function of temperature: for warmer air
column, pressure decreases more slowly with height.
€
¼ p0
½ p0
¾ p0
p0
Outline
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
Definition & scope of the climate system
Atmospheric temperature
Atmospheric composition
Atmospheric pressure
Atmospheric humidity
Ocean
Cryosphere
Land surface
Specific humidity: mass of H2O/mass of air; ranges
from 0 - 0.02 (or 20 g/kg)
If we compare the (H2O) vapor pressure with air
pressure as a function of height, what you will see is:
Think-Pair-Share: Why does
water vapor concentration
decrease with height at a
much faster rate than air
(basically N2+O2) pressure?
The “e-folding” height for
H2O is about 3 km.
Latitudinal variation of water vapor
Latitude of NYC: ~ 8 g/kg
of water vapor in the air
Outline
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
Definition & scope of the climate system
Atmospheric temperature
Atmospheric composition
Atmospheric pressure
Atmospheric humidity
Ocean
Cryosphere
Land surface
Water in various reservoirs
Reservoir
Depth if spread over
the entire surface of
the Earth (m)
Percentage
Oceans
2,650
97
Icecap/glacier
60
2.2
Ground water
20
0.7
Lakes/streams
0.35
0.013
Soil moisture
0.12
0.013
Atmosphere
0.025
0.0009
Total
2,730
100
Average ocean depth: 3,729 m.
- Climate of the atmosphere: temperature & precipitation
- Climate of the ocean: temperature and salinity (determining
water density and circulation)
Density: Latitude-depth cross section
Water can slide along
these lines.
Density of the
ocean is
determined by
its temperature
and salinity
Dense water
goes down; light
water comes up.
Outline
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
Definition & scope of the climate system
Atmospheric temperature
Atmospheric composition
Atmospheric pressure
Atmospheric humidity
Ocean
Cryosphere
Land surface
Cryosphere: Snow and various forms of ice (e.g., ice sheet, sea
ice, etc.) near the surface of the Earth.
2% of the water on Earth is frozen. Frozen water is about 80% of
the fresh water. Most of ice mass is in the great ice sheets of
Antarctica (89%) and Greenland (8.6%).
Cryosphere is important to climate mostly because snow and
ice are good reflector of sunlight (high albedo). So, snow/ice
coverage is an important parameter to monitor.
Continental ice sheet:
3.1% of the Earth
Seasonal snow:
9.8% of the Earth
Sea ice:
4.5% of the Earth
-------------------------------------------------------------Total coverage:
17.4% of the Earth
Outline
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
Definition & scope of the climate system
Atmospheric temperature
Atmospheric composition
Atmospheric pressure
Atmospheric humidity
Ocean
Cryosphere
Land surface
In terms of the climatic importance, land surface influences
climate in the following ways:
1)  Affects absorption of solar radiation (e.g., forest Vs desert)
2)  Topography affects regional climate (e.g., Himalaya and
Rocky blocking airflow)
3)  Carbon cycle
Land use: roughly speaking, 1/3 is used for crops and
animals, 1/3 is forest, and the remaining 1/3 desert/tundra.