Global Warming Archer chapters 1 & 2

1. Global WarmingArcher chapters 1 & 2 GEO 307 Dr. Garver

2. Chapter 1: Humankind & Climate • There is no doubt the Earth is warming. • Is it us? • What evidence are we seeing? • Weather vs. Climate • What’s the difference?

3. Human induced changes are expected to be small compared to variability. • T in this century expected to rise a few deg. • Hard to calculate a change in the avg. when the variability is so much greater than the trend. • In addition there is long term climate change. • Little Ice Age - 1650-1800 • Last glacial maximum (20,000 ybp) was only 5-6 deg C cooler than today

4. Little Ice Age • Period of cooling 1550 AD and 1850 AD - after Medieval Climate Optimum

5. Forecasting Climate Change • T of Earth is determined by balance of energy in and energy out. • Sun drives earth's climate, heats the earth's surface; earth radiates energy back into space. • It is possible to change the T of Earth by changing either incoming or outgoing energy.

6. Climate Forcing: • Sunspots change output of sun • Changing reflection of Earth • Greenhouse effect

7. Most gases in the atmosphere are not gh gases. • Greenhouse gases (water vapor, carbon dioxide, methane) trap some of the outgoing energy. • Water vapor is tricky, it amplifies the warming effects from changes in other gh gases. • Without "greenhouse effect," T would be much lower, life would not be possible.

8. Human Activity • Carbon dioxide - burning fossils fuels • Methane - landfills, livestock, rice cultivation • Particulates - smokestacks, combustion engines.

9. Asessing the Risk • Forecast is an increase of 2-5 deg by 2100. • Models - Used to forecast increase in T and the results of that increase. • many are economic

10. Greenhouse Effect

11. Chapter 2: Blackbody Radiation • Electromagnetic Radiation • Energy travels through a vacum from Sun to Earth. • Objects can absorb energy and re-emit it. • Black Body- any object that is a perfect emitter and a perfect absorber of radiation • sun and earth's surface behave approximately as black bodies.

12. Radiant energy • transfer of energy via electromagnetic waves. • Radiation • examples: • sun warms your face • apparent heat of a fire • wavelength, frequency

13. Energy through a vacum • EMR - travels as wavelengths • c= speed of light, constant • relates frequency to wavelength. • fig 2.2

14. Common wavelengths • units of micrometers are often used to characterize the wavelength of radiation • 1 micrometer = 10-6 meters • paper is about 100 micrometers thick

15. Radiation emitted by objects • All objects that have a T greater than 0 deg K emit radiation • hot objects emit more radiation that colder objects • Need to know much radiation is being emitted by an object, and at what wavelengths.

16. Black Body Radiation • Black Body- any object that is a perfect emitter and a perfect absorber of radiation • sun and earth surfaces behave approximately as black bodies

17. Stefan-Boltzman Law • relates the total amount of radiation emitted by an object to its temperature: E=sT4 where: E = total amount of radiation emitted by an object per square meter (Watts m-2) s is a constant = 5.67 x 10-8 Watts m-2 K-4 T is the temperature of the object

18. Josef Stefan,  (1835 – 1893)  Austrian physicist - 1879 formulated a law which states that the radiant energy of a black body is proportional to the fourth power of its temperature. • One first important steps toward understanding of radiation. • Five years after he derived his law empirically, it was derived theoretically by Ludwig Boltzmann of Austria and hence became known as the Stefan–Boltzmann law.

19. Weins Law • Most objects emit radiation at many wavelengths • There is one wavelength where an object emits the largest amount of radiation lmax = 2897 mm K/ T(K) • At what wavelength does the sun emit most of its radiation? • At what wavelength does the earth emit most of its radiation?

20. Also called Wien’s displacement law • Named after German physicist Wilhelm Wien, who received the Nobel Prize for Physics in 1911 for discovering the law.

21. Temperature Scales • Kelvin • Celsius • Fahrenheit • Temperature Conversions: ºC = 5/9(ºF-32) K = ºC + 273 Absolute zero at 0 K is −273.15 °C (−459.67 °F)

22. What are the similarities and differences between the Sun and Earth radiation curves?

23. percentages in each wavelength band

24. Radiative Equilibrium If the T of an object is constant with time, the object is in radiative equilibrium at Te What happens if energy input > energy output? What happens if energy input < energy output? Is the earth in radiative equilibrium?

25. Radiative Equilibrium for the Earth • Energy gained through absorption of short wave radiation is equal to the emitted long wave radiation • So, what is the radiative equilibrium temperature for the earth?

26. Radiative Equilibrium Temperature for the Earth • Use Stefan-Boltzman Law • Simplified case of no atmosphere • Te = 255 Kelvin • earth should be frozen! • actual Te = 288 K

27. Earth emits 240 Watts m2 Using E = sTe4 then Te = (E/s)1/4 • So, for the simplified case of no atmosphere Te= 255 K • But Te = 288 K • What is the reason for why the observed Te is warmer than what we calculated using the Stefan-Boltzman law???

29. Interaction of Solar Radiation and the Atmosphere • Based on last figure, ~1/2 of incoming sw radiation makes it to surface • ~19% is absorbed by gasses in the atmosphere • Therefore, the atmosphere is fairly transparent to incoming solar radiation. • Does the atmosphere have interaction with lw radiation emitted by earth???

30. Earth – Range of primary wavelengths Sun – Range of primary wavelengths

31. Interaction of Long Wave Radiation and the Atmosphere • Some lw radiation emitted by earth escapes to space • Some lw is absorbed by gasses in atmosphere • These gasses then re-emit some =lw radiation back to the ground • The additional lw radiation reaching the ground further warms the earth • This is known as the "greenhouse effect"

32. Methane (CH4) • Carbon Dioxide (CO2) • Ozone (O3) • Water Vapor (H2O) • Nitrous Oxide (N2O)