Chapter 1 Introduction to the Climate Chapter 1 Introduction to the Climate SystemSystem

This chapter discusses:This chapter discusses:

1.1. Earth’s atmosphereEarth’s atmosphere2.2. OceansOceans3.3. Cryosphere (sea ice/glacial ice)Cryosphere (sea ice/glacial ice)4.4. Land and biosphereLand 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 AirTRACE GASES

Argon (.93%) andCarbon Dioxide (.03%)Ozone (.000004%)

Water vapor is constantly beingadded and subtracted from the atmosphere, and varies from near0% (deserts) to 3-4% (warm, tropical oceans and jungles)

Solid particles (dust, sea salt, pollution) also exist

Greenhouse GasesGreenhouse 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

• 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

CO2

CH4

N2O

• Increased 150% 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 • 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%

Global, well-mixed greenhouse gas (GHG) concentrations

1000 1200 1400 1600 1800 2000Year

1000 1200 1400 1600 1800 2000Year

CO2

CH4

N2O

• Increased 150% since 1750 to its highest levels in at least 420,000 years

• 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%

1000 1200 1400 1600 1800 2000Year

Changing Atmospheric Composition:

Indicators of the Human Influence

• 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

Global, well-mixed greenhouse gas (GHG) concentrations

1000 1200 1400 1600 1800 2000Year

CO2

CH4

N2O

• Increased 16% since 1750 to its highest levels in at least 1,000 years

1000 1200 1400 1600 1800 2000Year

Changing Atmospheric Composition:

Indicators of the Human Influence

• Increased 150% since 1750 to its highest levels in at least 420,000 years

• 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

Global, well-mixed greenhouse gas (GHG) concentrations

Atmospheric CO2 Since 1750

Composition of the Present Atmosphere Venus Earth

Mars

Surface Pressure 100,000 mb 1,000 mb 6 mb

CO2 >98% 0.03% 96%N2 1% 78% 2.5%Ar 1% 1% 1.5%O2 0.0% 21% 2.5%H2O 0.0% 0.1% 0–0.1%

The Vertical Structure of Earth’s AtmosphereThe Vertical Structure of Earth’s AtmosphereFour Four layers: layers:

TroposphereTroposphere (overturning(overturning) )

StratosphereStratosphere (stratified) (stratified)

From surface to 8-18 kmFrom surface to 8-18 km

From troposphere top to 50 From troposphere top to 50 kmkm

MesospherMesospheree

ThermosphereThermosphere

Absorption of solar Absorption of solar radiation by Oradiation by O33

Extremely thin air; very Extremely thin air; very low temperaturelow temperature

Extremely thin air; very Extremely thin air; very high temperaturehigh temperature

Vertical Structure of the Atmosphere

4 distinct layersdetermined bythe change oftemperaturewith 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 layersdetermined bythe change oftemperaturewith 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 layersdetermined bythe change oftemperaturewith 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 layersdetermined bythe change oftemperaturewith 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 AtmosphereVertical Structure of Earth’s Atmosphere

1. Four layers defined by

temperature

2. Importance to climate and climate change

Troposphere:

Troposphere:Stratosphere:Mesosphere:Thermosphere:

T decreases with altitudeT increases with altitudeT decreases with altitudeT increases with altitude

Contains 80% of Earth’s gases Contains 80% of Earth’s gases

Most of Earth’s weather occursMost of Earth’s weather occurs

Most of the measurements is availableMost of the measurements is available

Stratosphere:

Contains 19.9% of Earth’s gases Contains 19.9% of Earth’s gases

Ozone layer: Ozone layer:

Blocking Sun’s ultraviolet Blocking Sun’s ultraviolet radiationradiation

Atmospheric TemperatureAtmospheric Temperature

1. Most widely recognized climatic variable(Global warming)

2. The lapse rate

Γ ≡ – ∂T/∂z, Γ > 0 in the troposphere

Tc = TK – T0

Tc = temperature in degrees Celsius (°C) = 5(TF – 32)/9

T0 = 273.15 K = the freezing pointGlobal mean surface temperature = 288 K, 15°C, 59°F

TK = thermodynamic temperature in kelvins (K)

* Varies with altitude, season and * Varies with altitude, season and latitudelatitude* Global mean = 6.5 K km* Global mean = 6.5 K km-1-1

* Determined by a balance * Determined by a balance between radiative cooling and between radiative cooling and convection of heatconvection of heat

* * ΓΓ< 0, temperature inversion< 0, temperature inversion

At high latitudes in winter and At high latitudes in winter and springspring

Atmospheric Temperature (continued)Atmospheric Temperature (continued)

3. Pole-to-pole distribution of zonal-mean temperature

4. Geographic distributions

* Land heats up and cools down much more quickly than oceans, hence larger seasonal variations.

* 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

* * Large seasonal variations in North America and Asia

* Smaller seasonal variations in * Smaller seasonal variations in the Southern Hemisphere.the Southern Hemisphere.

See IRI Data Library

Annual Climate in Seattle

Atmospheric PressureAtmospheric Pressure

Pressure=Force/Pressure=Force/AreaArea

Pressure decreases Pressure decreases with altitude.with altitude.

Gravity pulls gases Gravity pulls gases toward earth's toward earth's surface, and the surface, and the whole column of whole column of gases weighs 14.7 psi gases weighs 14.7 psi at sea level, a at sea level, a pressure of 1013.25 pressure of 1013.25 mb or 29.92 in.Hg.mb or 29.92 in.Hg.

Standard sea level Standard sea level pressure = 101325 Pa pressure = 101325 Pa = 101.325 kPa = = 101.325 kPa = 1013.25 mb1013.25 mb

Vertical Pressure ProfileVertical Pressure Profile

Pressure decreases at a Pressure decreases at a curved rate curved rate proportional to altitude proportional to altitude squared, but near the squared, but near the surface a linear surface a linear estimate of 10 mb per estimate of 10 mb per 100 meters works well.100 meters works well.

Hydrostatic BalanceHydrostatic Balance

Force = Mass Force = Mass × × AccelerationAcceleration

Given a Given a unit areaunit area with with thickness dz, volume = thickness dz, volume = dz, mass = dz, mass = ρρdz dz

Gravity force= g Gravity force= g ρρdzdzPressure force= –dp Pressure force= –dp

Without atmospheric Without atmospheric motions, motions, ––dp = gdp = gρρ dzdzdp/dz = – dp/dz = – ρρgg

p(z) = p(z) = ∫∫zz∞ ∞ ρρg dzg dz

m(z)=p(z)/gm(z)=p(z)/gm(0)=p(0)/g=pm(0)=p(0)/g=pss/g/g

=1.03=1.03××10104 4 kg mkg m–2–2

dz

z

p

p+dp -dp

gρdz

Hydrostatic Balance (continued)Hydrostatic Balance (continued)dp/dz = – dp/dz = – ρρgg

For an ideal gas, For an ideal gas, p=p=ρρRRTTwhere the gas constant where the gas constant R = 287 J KR = 287 J K-1 -1 kgkg-1-1

dp/dz=–pg/(RT)dp/dz=–pg/(RT)dp/p= –dz/Hdp/p= –dz/Hd d lnlnp= –dz/Hp= –dz/Hwhere H=Rwhere H=RTT/g=scale /g=scale heightheight

If the atmosphere is If the atmosphere is isothermal,isothermal,∫∫psps

p p d d lnlnp= p= ∫∫00zz –dz/H–dz/H

p=pp=pssexpexp(–z/H)(–z/H)

H = 7.6 km for the H = 7.6 km for the mean Tmean T

dz

z

p

p+dp -dp

gρdz

Water VaporWater Vapor1. Highly variable spatially

2. Importance to climate and climate change

* Important part of the water cycle; ocean-to-land atmospheric vapor transport balances land-to-ocean runoff.

• 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

* 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.

OceansArea: covers ~70% of Earth’s surfaceArea: covers ~70% of Earth’s surfaceVolume: ~97% of all the water on EarthVolume: ~97% of all the water on EarthDepth: ~3.5 kilometersDepth: ~3.5 kilometersAlbedo: 5-10%, lowest on Earth’s surfaceAlbedo: 5-10%, lowest on Earth’s surfaceHeat capacity: high; thermal inertia: highHeat capacity: high; thermal inertia: highTemperature: less variable than in the atmosphereTemperature: less variable than in the atmosphereFreezing point: –1.9Freezing point: –1.9°°C, not 0C, not 0°°CCSalinity: water and dissolved salts; most common salt: table salt (NaCl).Salinity: water and dissolved salts; most common salt: table salt (NaCl).Density: 1034-1035 kg/mDensity: 1034-1035 kg/m33 (greater than pure water 1000kg/m (greater than pure water 1000kg/m33))Average salinity = 35 parts per thousand (ppt) or 3.5% by weightAverage salinity = 35 parts per thousand (ppt) or 3.5% by weightDensity depends on temperature and salinity:Density depends on temperature and salinity:

Cold water Cold water high density high density Formation of sea ice Formation of sea ice high density high densityEvaporation Evaporation high salinity high salinity high density high densityPrecipitation and river discharge Precipitation and river discharge low salinity low salinity low density low density

Two main forms of circulationTwo main forms of circulationSurface currents: wind-driven, horizontal, surface waters, fastSurface currents: wind-driven, horizontal, surface waters, fastDeep-ocean circulation: thermohaline, vertical, deep waters, slowDeep-ocean circulation: thermohaline, vertical, deep waters, slow

Surface is not level due to currents, waves, atmosphere pressure, and Surface is not level due to currents, waves, atmosphere pressure, and variation in gravity.variation in gravity.

Sea Ice

Locations: Locations: in the Arctic Ocean in the Arctic Ocean surrounded by landmass;surrounded by landmass;

Depth: ~1–4 m in the Arctic; ~1 m in Depth: ~1–4 m in the Arctic; ~1 m in the Southern Ocean.the Southern Ocean.

Albedo: 60-90%, highest on Earth’s surfaceAlbedo: 60-90%, highest on Earth’s surface

Density: less than seawater, hence floats on top.Density: less than seawater, hence floats on top.

The role in the climate system:The role in the climate system:Albedo-temperature feedbackAlbedo-temperature feedbackPrevents the underlying (warm) ocean from interaction with the Prevents the underlying (warm) ocean from interaction with the

atmosphere, thus cools the air.atmosphere, thus cools the air.MeltingMelting of sea ice of sea ice extracts heatextracts heat from the atmosphere; from the atmosphere; FormationFormation of sea ice of sea ice

releases heatreleases heat to the atmosphere. to the atmosphere.

in the Southern Ocean, in the Southern Ocean, surrounding Antarctica.surrounding Antarctica.

Longevity: in the Arctic, 4–5 yrs; in the Southern Ocean, forms and melts Longevity: in the Arctic, 4–5 yrs; in the Southern Ocean, forms and melts yearly.yearly.

Glacial Ice

Two forms:Two forms:

Sizes:Sizes:

Albedo:Albedo:

The role in the climate system:The role in the climate system:

Albedo-temperature feedbackAlbedo-temperature feedback

Stores 70% of world’s fresh waterStores 70% of world’s fresh water

Continental ice sheets.Continental ice sheets.

Locations:Locations:

Mountain (alpine) glaciersMountain (alpine) glaciers

Near sea-level at hi. lat.Near sea-level at hi. lat.> 5 km near equator> 5 km near equatorAntarctica and Greenland (polar ice caps)Antarctica and Greenland (polar ice caps)

A few km in length, tens to hundreds of m in width and thickness.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.Hundred to thousands of km in length, 1–4 km in thickness.Area of the two current ice sheets:Area of the two current ice sheets:

~11% of land surface; ~11% of land surface; 70 m70 m sea level rise when all melted. sea level rise when all melted.Movement:Movement: Flows downhill by gravity along mountain valleysFlows downhill by gravity along mountain valleys

Flows to the lower margins.Flows to the lower margins. The weight depresses bedrock.The weight depresses bedrock.

60-90%, highest on Earth’s surface60-90%, highest on Earth’s surface

Changes salinity, circulation and sea Changes salinity, circulation and sea level when meltlevel when melt

Example of a positive feedback

If this were the only mechanism acting, we’d get a runaway temperature increase

Albedo decreases Less solar energy reflected

Warm temperatures

More energy retained in system

Ice and snow melt

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.

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

Global Climate Pattern and Vegetation

Satellite-Derived Plant Geography

Early maps areconstructed based on atlas, surface surveys.

Emphasize climatefactors (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.