How much can we change the Environment?How much can we change the Environment?

Locally – easy to see

Globally – do you believe it?– How many believe we, mere humans, can change the

climate?

– Can you give examples of any human / other life forms changing the climate of the earth?

Atmospheric Composition and ClimateAtmospheric Composition and Climate

Why do we worry about these simple stuff?– Evolution => Composition

– Composition => Thermal Structure

– Thermal Structure => Dynamics

The most basic question in the climate change debate is not whether the climate is changing, but are we changing the composition of the atmosphere, and hence the climate, too rapidly?

Evolution of the AtmosphereEvolution of the Atmosphere

“BIG BANG”

1. First atmosphere – one of cosmic gases: H2 - Hydrogen He - Helium

CH4 - Methane NH3- Ammonia

H2O - Water vapor CO2 - Carbon Dioxide

NOx - Oxides of Nitrogen

Evolution of the AtmosphereEvolution of the Atmosphere High temperatures probably drove off primeval

atmosphere.

Second Atmosphere: nothing -- similar to the moon, everything gone!

Third Atmosphere: developed from secondary sources such as outgassing from volcanoes, geysers, cracks, etc…

What is the current estimate of the Age of the Earth???

Evolution of the AtmosphereEvolution of the Atmosphere

H2Ov - 68%

After the Earth cooled

H2Ov - 15%

Composition ofVolcano Effluent

oceans

rainAs the earth cooled, the watervapor condensed and created

the oceans, etc.

First bacteria evolved maybe four billion years ago (anaerobic).

About 2-3 billion years ago green plants appeared in the oceans (algae). Why oceans?

Because liquid water (H2O) screens out ultraviolet radiation (UV).

Photosynthesis:

CO2 + sunlight + chlorophyll

O2 + organic material

Evolution of the AtmosphereEvolution of the Atmosphere

100 %

50 %

0%

Billions of years before present

5 3 2 1 0

CO2

O2

4

App

roxi

mat

e C

omp

ositi

on

Evolution of the AtmosphereEvolution of the Atmosphere There were no plants and animals on land until nearly

400 million years ago. Why?

Photodissociation by solar radiation

Photo-dissociationPhoto-dissociation Higher energy EM waves can “photodissociate,” or break

apart, certain larger molecules. UV radiation can photodissociate DNA molecules. Without protection from the atmosphere, life (as we know

it) could not live on land. What is the change that allowed the development of

terrestrial life?– UV radiation can also photodissociate other molecules such as

oxygen (formed via photosynthesis).

Timeline of Earth’s EvolutionTimeline of Earth’s Evolution

4.6 bya Formation of the Earth3.5 bya Abiotic synthesis, 3.2 bya Denitrification 2.3 bya Oxygen-producing photosynthesis by

cyanobacteriaStart of ozone formation

Evolution of the AtmosphereEvolution of the Atmosphere

4 Billion Years Ago

UV Radiation

Today

UV Radiation

Most of the UV radiation is screened from the earth’s surface, usually absorbed at altitudes above 20-40 km.

Chapman ProcessChapman Process

1. O2 + UV O + Oupper atmosphere

2. O2 + O + Body O3 + Body3-body production of ozone

3. O3 + UV O + O2

absorption of UV by ozone

4. O3 + O 2O2

removal process of ozone

Impact of above processes:– More oxygen, more ozone– Reduction of UV arriving lower atmosphere– Warming up of the middle atmosphere

Chapman ProcessChapman Process

High energy radiation

O2

concentration

Hei

ght

Ozone layerwarming in the

middle atmosphere

Ultraviolet RadiationUltraviolet Radiation

Evolution of the AtmosphereEvolution of the Atmosphere

Current Atmosphere

O2 21 % Increased via photosynthesis

Argon 1 % Increased via the radioactive decay of potassium ( K

)

CO2 0.03 % Decreased via photosynthesis

H2Ov 0 - 4 % Most variable component

also particulates and trace gases

N2 78 % Why ?

Evolution of the AtmosphereEvolution of the Atmosphere Why so much Nitrogen (78%)?

– Outgassing adds approximately 1 “unit”

– Lightning removes 4 to 10 units

– Nitrogen fixing by bacteria removes 20 to 100 units

– Anaerobic bacteria (probably in the oceans) adds the balance

Volcanoes

AnaerobicBacteria

Nitrogen FixingBacteria

Lightning

Earth

The Nitrogen in our atmosphere is primarily a result of thebalance of these four processes.

Timeline of Earth’s EvolutionTimeline of Earth’s Evolution

4.6 bya Formation of the Earth3.5 bya Abiotic synthesis, 3.2 bya Denitrification 2.3 bya Oxygen-producing photosynthesis by

cyanobacteriaStart of ozone formation

1.8 bya Nitrification (aerobic)1.5 bya Nitrogen fixation (aerobic)1.4 bya Earliest eukaryotes0.57 bya First shelled invertebrates0.43-0.5 bya Primitive fish0.395-0.43 bya First land plants -- oxygen and ozone

increase

Evolution of the Atmosphere (Summary)Evolution of the Atmosphere (Summary)

99 % of our present atmosphere is directly a result of life processes.

These life processes are primarily– Life cycles of nitrogen fixing bacteria

– Anaerobic bacteria

– Photosynthesis

Human can substantially impact the environment– CFC and Ozone Hole

Electromagnetic SpectrumElectromagnetic Spectrum

Black Body RadiationBlack Body Radiation

Stefan-Boltzmann’s Law of Black Body Radiation (1879/1884)

Wien’s Displacement Law (1894)

K)m(2898constantmax T

Peak wavelength of radiative emission for the sun and the earth?

Radiation Spectra

10-28

10-20

10-12

10-4

104

1012

1020

1028

1036

10-6 10-4 10-2 100 102 104 106 108 1010 1012

10-6 10-4 10-2 100 102 104 106 108 1010 1012R

adia

tion

int

ensi

ty (

W m

-2

m-1)

Wavelength (m)

60

00

K15

mil

lio

n K

Gam

ma X

UV

Vis

ible

Infr

ared

Sh

ort

rad

io

AM

rad

io

Lo

ng

rad

io

Tel

evis

ion

& F

M r

adio

30

0 K

1 K

Rad

iati

on in

tens

ity

(W m

-2

m-1)

Ultraviolet and Visible Spectra of the Sun

Figure 2.5

2 103

4 103

6 103

8 103

1 104

1.2 104

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Rad

iati

on in

tens

ity

(W m

-2

m-1)

Wavelength (m)

UV

-BU

V-A

Visible

FarUV

NearUV

Red

Green

Blue

Rad

iati

on in

tens

ity

(W m

-2

m-1)

Ultraviolet RadiationUltraviolet Radiation

Question: what would be the temperature of earth if there is no atmosphere?

Radiative EquilibriumRadiative Equilibrium

Solar radiation (r2) So ~ 1370 W m-2 Earth’s IR radiation (4r2

Radiative EquilibriumRadiative Equilibrium Fate of incident solar

radiation– 30 % reflected (albedo)

– 19 % absorbed by the atmosphere & clouds

– 51 % absorbed by the ground

Atmospheric OpacityAtmospheric Opacity

CO2, CH4, N2O, H2O…

Surface absorption

Solar shortwave Su

rfac

e lo

ngw

ave

Temperature increase

Greenhouse effect：Greenhouse gases absorbs longwave radiation from surface, making the atmosphere warmer. Without Greenhouse effect, temperature of earth is -18℃, not the current 15℃.

The Earth’s atmosphere is largely transparent to incident sunlight. It passes through and warms the surface of the Earth to a temperature of order 300 K.

Approximating the Earth as a blackbody and applying Wien’s Law, it’s easy to see that the Earth re-emits the energy at a wavelength = 3 x 106/300 = 104 nm, which is in the IR.

Carbon dioxide, it turns out, is an effective absorber of IR radiation. Therefore, solar energy is trapped in the Earth’s atmosphere. That’s good, because it moderates the climate.

Up to a point.

Increasing amounts of CO2 in the atmosphere trap increasing amounts of heat, leading to a global temperature increase. The consequences of can be catastrophic!

Planet Venus Earth Mars

CO2

96 bar

(96%)

1 bar

0.03%

0.007 bar

(95%)

Surface

Temperature450 C 15 C -55 C