Transcript Components of the Climate System

Chapter 1 Introduction to the Climate
System
This chapter discusses:
1.
2.
3.
4.
Earth’s atmosphere
Oceans
Cryosphere (sea ice/glacial ice)
Land and biosphere
The Effects of the Atmosphere
 Blocks ultraviolet radiation
 Meteors burn
 Sound waves can travel
 Birds and airplanes can fly
 Diffuses heat
 Scatters sunlight (blue skies and sunsets)
 Hydrologic cycle
 Weather and climate
The Atmosphere
 A thin envelope around the planet
 90% of its mass (5.1 x 1018 kg) is within 16 km (10 mi) of the
surface (about 0.0025 times the radius of the Earth)
 Atmospheric motions can therefore be considered to occur
“at” the Earth’s surface
 The basic chemical composition of dry air is very uniform across the
globe and up to about 100 km
 The greatest and most important variations in its composition involve
water in its various phases
 Water vapor
 Clouds of liquid water
 Clouds of ice crystals
 Rain, snow and hail
Composition of the Atmosphere
Dry Air
TRACE GASES
Argon (.93%) and
Carbon Dioxide (.03%)
Ozone (.000004%)
Solid particles (dust, sea salt,
pollution) also exist
Water vapor is constantly being
added and subtracted from the
atmosphere, and varies from near
0% (deserts) to 3-4% (warm,
tropical oceans and jungles)
Greenhouse Gases
• Nitrogen, Oxygen and Argon (99.9% volume mixing
ratio) have only limited interaction with incoming
solar radiation, and they do not interact with the
infrared radiation emitted by the Earth
• A number of trace gases (carbon dioxide, methane,
nitrous oxide, and ozone) do absorb and emit
infrared radiation (as does water vapor)
• Water vapor, carbon dioxide and ozone also absorb
solar shortwave radiation
• Because they emit infrared radiation up- and
downward, these greenhouse gases increase the
energy received at the Earth’s surface, thus raising
the temperature
Changing Atmospheric Composition:
Indicators of the Human Influence
Global, well-mixed greenhouse gas
(GHG) concentrations
CO2
• 31% increase since 1750: Highest levels
since at least 420,000 years ago
• Rate of increase unprecedented over
at least the last 20,000 years
1000
1200
1400
1600
Year
1800
2000
CH4
• Increased 150% since 1750 to its highest
N2O
• Increased 16% since 1750 to its highest
levels in at least 420,000 years
• Has both natural (e.g., wetland) and
human-influenced sources (e.g., landfills,
agriculture, natural gas activities)
• Accounts for 20% of total GHG forcing
levels in at least 1,000 years
• Has both natural (e.g., soils and oceans)
and anthropogenic sources
• Accounts for 6% of total GHG forcing
• Halocarbons (e.g., CFCs) account for 14%
Changing Atmospheric Composition:
Indicators of the Human Influence
Global, well-mixed greenhouse gas
(GHG) concentrations
CO2
• 31% increase since 1750: Highest levels
since at least 420,000 years ago
• Rate of increase unprecedented over
at least the last 20,000 years
CH4
• Increased 150% since 1750 to its highest
levels in at least 420,000 years
1000
1000
1200
1200
1400
1400 1600
1600
Year
Year
1800
1800
2000
N2O2000
• Increased 16% since 1750 to its highest
levels in at least 1,000 years
• Has both natural (e.g., soils and oceans)
and anthropogenic sources
• Accounts for 6% of total GHG forcing
• Halocarbons (e.g., CFCs) account for 14%
Changing Atmospheric Composition:
Indicators of the Human Influence
Global, well-mixed greenhouse gas
(GHG) concentrations
CO2
• 31% increase since 1750: Highest levels
since at least 420,000 years ago
• Rate of increase unprecedented over
at least the last 20,000 years
CH4
• Increased 150% since 1750 to its highest
levels in at least 420,000 years
N2O
• Increased 16% since 1750 to its highest
levels in at least 1,000 years
1000
1200
1400
1600
Year
1800
2000
Atmospheric CO2 Since 1750
Composition of the Present Atmosphere
Venus
Earth
Surface Pressure
100,000 mb
1,000 mb
CO2
N2
Ar
O2
H2 O
>98%
1%
1%
0.0%
0.0%
0.03%
78%
1%
21%
0.1%
Mars
6 mb
96%
2.5%
1.5%
2.5%
0–0.1%
The Vertical Structure of Earth’s Atmosphere
Four layers:
Troposphere
(overturning)
From surface to 8-18 km
Stratosphere
(stratified)
From troposphere top to 50 km
Absorption of solar radiation
by O3
Mesosphere
Extremely thin air; very low
temperature
Thermosphere
Extremely thin air; very high
temperature
Vertical Structure of the Atmosphere
4 distinct layers
determined by
the change of
temperature
with height
Extends to 10 km in the extratropics, 16 km in the tropics
Contains >80% of the atmospheric mass, and 50% is
contained in the lowest 5 km (3.5 miles)
It is defined as a layer of temperature decrease
The total temperature change with altitude is about 72°C
(130°F), or 6.5°C per km (lapse rate)
• It is the region where most weather occurs, and it is kept
well stirred by rising and descending air currents
• Near 11 km resides the “jet stream”
• The transition region of no temperature change is the
“tropopause”: it marks the beginning of the next layer
Vertical Structure of the Atmosphere
4 distinct layers
determined by
the change of
temperature
with height
Extends to about 50 km
It is defined as a layer of temperature increase and
is stable with very little vertical air motion – a good place to fly!
Why does temperature increase? In part because of ozone, formed
as intense ultraviolet solar radiation breaks apart oxygen molecules
• Near the ozone maximum (about 25 km), there are still only
12 ozone molecules for every million air molecules
• Yet, the absorption of ultraviolet radiation by ozone shields the
surface and warms the stratosphere
• The transition region to the next layer is the “stratopause”
Vertical Structure of the Atmosphere
4 distinct layers
determined by
the change of
temperature
with height
Extends to about 85 km
Few ozone molecules, and the extremely thin air loses more energy
than it gains, so the temperature decreases with height
With so few molecules to scatter light, the sky is dark
The air pressure is 1000 times lower than at the surface
(99.9% of the atmosphere’s mass is below the mesosphere)
Exposure to solar radiation would severely burn our bodies!
The transition region to the next layer is the “mesopause”
Vertical Structure of the Atmosphere
4 distinct layers
determined by
the change of
temperature
with height
Contains 0.01% of the atmospheric mass
An air molecule can travel 1 km before colliding with another!
If we measure temperature with a thermometer, the reading
is near absolute zero (0 K, or -460°F), not 1500°F. Why?
The temperature of a gas is related to the average speed at
which molecules are moving
Even though air molecules in this region are zipping around at very
high speeds, there are too few to bounce off a thermometer bulb
to transfer energy to record a reading
This explains why astronauts on space walks can survive such high
temperatures: the traditional meaning of “hot” and “cold” is no
longer applicable
Vertical Structure of Earth’s Atmosphere
1. Four layers defined by temperature
Troposphere: T decreases with altitude
Stratosphere: T increases with altitude
Mesosphere:
T decreases with altitude
Thermosphere: T increases with altitude
2. Importance to climate and climate change
Troposphere:
Contains 80% of Earth’s gases
Most of Earth’s weather occurs
Most of the measurements is available
Stratosphere:
Contains 19.9% of Earth’s gases
Ozone layer:
Blocking Sun’s ultraviolet radiation
Atmospheric Temperature
1. Most widely recognized climatic variable (Global warming)
T c = TK – T 0
Tc = temperature in degrees Celsius (°C) = 5(TF – 32)/9
TK = thermodynamic temperature in kelvins (K)
T0 = 273.15 K = the freezing point
Global mean surface temperature = 288 K,
15°C, 59°F
2. The lapse rate
Γ ≡ – ∂T/∂z, Γ > 0 in the troposphere
* Varies with altitude, season and latitude
* Global mean = 6.5 K km-1
* Determined by a balance between
radiative cooling and convection of
heat
* Γ< 0, temperature inversion
At high latitudes in winter and spring
Atmospheric Temperature (continued)
3. Pole-to-pole distribution of zonal-mean temperature
* Greatest near the equator, > 26°C; lowest at the poles
* Stronger seasonal cycle in the Northern Hemisphere than in
the south
* Amplitude of the seasonal cycle
decreases from the poles to the equator
4. Geographic distributions
* Land heats up and cools down
much more quickly than oceans,
hence larger seasonal variations.
* Large seasonal variations in North
America and Asia
* Smaller seasonal variations in the
Southern Hemisphere.
See IRI Data Library
Annual Climate in Seattle
Atmospheric Pressure
Pressure=Force/Area
Pressure decreases
with altitude.
Gravity pulls gases
toward earth's
surface, and the
whole column of gases
weighs 14.7 psi at sea
level, a pressure of
1013.25 mb or 29.92
in.Hg.
Standard sea level
pressure = 101325 Pa
= 101.325 kPa =
1013.25 mb
Vertical Pressure Profile
Pressure decreases at a
curved rate
proportional to altitude
squared, but near the
surface a linear
estimate of 10 mb per
100 meters works well.
Hydrostatic Balance
Force = Mass ×
Acceleration
Given a unit area with
thickness dz, volume =
dz, mass = ρdz
-dp
p+dp
p
dz
gρdz
z
Gravity force= g ρdz
Pressure force= –dp
Without atmospheric
motions,
–dp = gρ dz
dp/dz = – ρg
p(z) = ∫z∞ ρg dz
m(z)=p(z)/g
m(0)=p(0)/g=ps/g
=1.03×104 kg m–2
Hydrostatic Balance (continued)
dp/dz = – ρg
For an ideal gas,
p=ρRT
where the gas constant
R = 287 J K-1 kg-1
-dp
p+dp
p
dz
gρdz
z
dp/dz=–pg/(RT)
dp/p= –dz/H
d lnp= –dz/H
where H=RT/g=scale
height
If the atmosphere is
isothermal,
∫psp d lnp= ∫0z –dz/H
p=psexp(–z/H)
H = 7.6 km for the
mean T
Water Vapor
1. Highly variable spatially
• Less than 1% in a dry atmosphere
• More than 3% in the moist tropics
• Decreases rapidly with altitude;
most is within a few km of the surface
• Decreases rapidly with latitude; at
the equator is 10 times that at the
poles
2. Importance to climate and climate change
* Important part of the water cycle; ocean-toland atmospheric vapor transport balances
land-to-ocean runoff.
* The most important greenhouse gas:
water vapor-temperature feedback.
* Water vapor condenses to form clouds, thus
clouds–radiation feedback. Clouds release
rainfall, reflect solar radiation, and reduce the
infrared radiation emitted by Earth.
Oceans
Area: covers ~70% of Earth’s surface
Volume: ~97% of all the water on Earth
Depth: ~3.5 kilometers
Albedo: 5-10%, lowest on Earth’s surface
Heat capacity: high; thermal inertia: high
Temperature: less variable than in the atmosphere
Freezing point: –1.9°C, not 0°C
Salinity: water and dissolved salts; most common salt: table salt (NaCl).
Density: 1034-1035 kg/m3 (greater than pure water 1000kg/m3)
Average salinity = 35 parts per thousand (ppt) or 3.5% by weight
Density depends on temperature and salinity:
Cold water  high density
Formation of sea ice  high density
Evaporation  high salinity  high density
Precipitation and river discharge  low salinity  low density
Two main forms of circulation
Surface currents: wind-driven, horizontal, surface waters, fast
Deep-ocean circulation: thermohaline, vertical, deep waters, slow
Surface is not level due to currents, waves, atmosphere pressure, and variation
in gravity.
Sea Ice
Locations: in the Arctic Ocean
surrounded by landmass;
in the Southern Ocean,
surrounding Antarctica.
Depth: ~1–4 m in the Arctic; ~1 m in
the Southern Ocean.
Longevity: in the Arctic, 4–5 yrs; in the Southern Ocean, forms and melts
yearly.
Albedo: 60-90%, highest on Earth’s surface
Density: less than seawater, hence floats on top.
The role in the climate system:
Albedo-temperature feedback
Prevents the underlying (warm) ocean from interaction with the
atmosphere, thus cools the air.
Melting of sea ice extracts heat from the atmosphere; Formation of sea ice
releases heat to the atmosphere.
Glacial Ice
Two forms: Mountain (alpine) glaciers
Continental ice sheets.
Locations: Near sea-level at hi. lat.
> 5 km near equator
Antarctica and Greenland (polar ice caps)
Sizes: A few km in length, tens to hundreds of m in width and thickness.
Hundred to thousands of km in length, 1–4 km in thickness.
Area of the two current ice sheets:
~11% of land surface; 70 m sea level rise when all melted.
Movement: Flows downhill by gravity along mountain valleys
Flows to the lower margins. The weight depresses bedrock.
Albedo:
60-90%, highest on Earth’s surface
The role in the climate system:
Stores 70% of world’s fresh water
Changes salinity, circulation and sea
level when melt
Albedo-temperature feedback
Example of a positive feedback
More energy
retained in system
Albedo decreases
Less solar energy
reflected
Warm temperatures
Ice and snow melt
If this were the only mechanism acting, we’d get a runaway temperature increase
The law of the minimum:
the factor that is least
available has the greatest
effect on plants.
The law of the maximum:
too much of a certain
factor also limits a plant’s
existence.
Global Climate Pattern and
Vegetation
Af: tropical wet (rainforest); Aw:
tropical wet and dry (savanna); Am:
tropical monsoon
Bs: dry semiarid (steppe); Bw: dry
arid (desert)
Cs: mediterranean; Cfa: humid
subtropical; Cfb: marine
Dw: dry winters; Ds: dry summers; Df:
wet all seasons
ET: polar tundra; EF: polar ice caps
Satellite-Derived Plant Geography
Early maps are
constructed based on
atlas, surface surveys.
Emphasize climate
factors (Precip, Temp).
Neglect human factors.
Satellite remote
sensing
provides global,
systematic,
continuous
measurements.
Monitor land use and
land cover changes.
Quantitative.
Must be validated by
comparing with
ground-based data.