How much can we change the Environment? n Locally – easy to see n 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 Climate n 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 Atmosphere “BIG BANG” 1. First atmosphere – one of cosmic gases: H 2 - Hydrogen He - Helium CH 4 - MethaneNH 3 - Ammonia H 2 O - Water vapor CO 2 - Carbon Dioxide NO x - Oxides of Nitrogen

Evolution of the Atmosphere n High temperatures probably drove off primeval atmosphere. n Second Atmosphere: nothing -- similar to the moon, everything gone! n 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 Atmosphere H 2 O v - 68% After the Earth cooled H 2 O v - 15% Composition of Volcano Effluent oceans rain As the earth cooled, the water vapor 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 (H 2 O) screens out ultraviolet radiation (UV).

Photosynthesis: CO 2 + sunlight + chlorophyll O 2 + organic material Evolution of the Atmosphere 100 % 50 % 0% Billions of years before present CO 2 O2O2 4 Approximate Composition

Evolution of the Atmosphere n There were no plants and animals on land until nearly 400 million years ago. Why? Photodissociation by solar radiation

Photo-dissociation n Higher energy EM waves can “photodissociate,” or break apart, certain larger molecules. n UV radiation can photodissociate DNA molecules. n Without protection from the atmosphere, life (as we know it) could not live on land. n 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 Evolution 4.6 byaFormation of the Earth 3.5 byaAbiotic synthesis, 3.2 byaDenitrification 2.3 byaOxygen-producing photosynthesis by cyanobacteria Start of ozone formation

Evolution 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 km.

Chapman Process 1.O 2 + UV  O + O upper atmosphere 2.O 2 + O + Body  O 3 + Body 3-body production of ozone 3.O 3 + UV  O + O 2 absorption of UV by ozone 4.O 3 + O  2O 2 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 Process High energy radiation O2O2 concentration Height Ozone layer warming in the middle atmosphere

Ultraviolet Radiation

Evolution of the Atmosphere n Current Atmosphere O 2 21 %Increased via photosynthesis Argon 1 % Increased via the radioactive decay of potassium ( K ) CO % Decreased via photosynthesis H 2 O v %Most variable component also particulates and trace gases N 2 78 %Why ?

Evolution of the Atmosphere n 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 Anaerobic Bacteria Nitrogen Fixing Bacteria Lightning Earth The Nitrogen in our atmosphere is primarily a result of the balance of these four processes.

Timeline of Earth’s Evolution 4.6 byaFormation of the Earth 3.5 byaAbiotic synthesis, 3.2 byaDenitrification 2.3 byaOxygen-producing photosynthesis by cyanobacteria Start of ozone formation 1.8 byaNitrification (aerobic) 1.5 byaNitrogen fixation (aerobic) 1.4 byaEarliest eukaryotes 0.57 byaFirst shelled invertebrates byaPrimitive fish byaFirst land plants -- oxygen and ozone increase

Evolution of the Atmosphere (Summary) n 99 % of our present atmosphere is directly a result of life processes. n These life processes are primarily –Life cycles of nitrogen fixing bacteria –Anaerobic bacteria –Photosynthesis n Human can substantially impact the environment –CFC and Ozone Hole

Electromagnetic Spectrum

Black Body Radiation n Stefan-Boltzmann’s Law of Black Body Radiation (1879/1884) n Wien’s Displacement Law (1894)

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

Radiation Spectra Radiation intensity (W m -2  m -1 )

Ultraviolet and Visible Spectra of the Sun Figure 2.5 Radiation intensity (W m -2  m -1 )

Ultraviolet Radiation

Question: what would be the temperature of earth if there is no atmosphere? Radiative Equilibrium Solar radiation (  r 2 ) S o ~ 1370 W m -2 Earth’s IR radiation (4  r 2 

Radiative Equilibrium n Fate of incident solar radiation –30 % reflected (albedo) –19 % absorbed by the atmosphere & clouds –51 % absorbed by the ground

Atmospheric Opacity

CO 2, CH 4, N 2 O, H 2 O… Surface absorption Solar shortwave Surface longwave 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℃.

n 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 l = 3 x 106/300 = 104 nm, which is in the IR. n 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. n Up to a point. n Increasing amounts of CO 2 in the atmosphere trap increasing amounts of heat, leading to a global temperature increase. The consequences of can be catastrophic!

PlanetVenusEarthMars CO 2 96 bar (96%) 1 bar 0.03% bar (95%) Surface Temperature 450 C15 C-55 C