11/14/2015 Global Warming Archer chapters 1 & 2 GEO 307 Dr. Garver

11/14/2015 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?

11/14/2015 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 Last glacial maximum (20,000 ybp) was only 5-6 deg C cooler than today

Little Ice Age Period of cooling 1550 AD and 1850 AD - after Medieval Climate Optimum 11/14/2015

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.

11/14/2015 Climate Forcing: Sunspots change output of sun Changing reflection of Earth Greenhouse effect

11/14/2015 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.

11/14/2015 Human Activity Carbon dioxide - burning fossils fuels Methane - landfills, livestock, rice cultivation Particulates - smokestacks, combustion engines.

11/14/2015 Asessing the Risk Forecast is an increase of 2-5 deg by Models - Used to forecast increase in T and the results of that increase. –many are economic

11/14/2015 Greenhouse Effect

11/14/2015 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.

11/14/2015 Radiant energy transfer of energy via electromagnetic waves. Radiation – examples: sun warms your face apparent heat of a fire wavelength, frequency

11/14/2015 Energy through a vacum EMR - travels as wavelengths c = speed of light, constant relates frequency to wavelength. fig 2.2

11/14/2015 Common wavelengths units of micrometers are often used to characterize the wavelength of radiation 1 micrometer = meters paper is about 100 micrometers thick

11/14/2015 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.

11/14/2015 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

11/14/2015 Stefan-Boltzman Law relates the total amount of radiation emitted by an object to its temperature: E=  T 4 where: E = total amount of radiation emitted by an object per square meter (Watts m -2 )  is a constant = 5.67 x Watts m -2 K -4 T is the temperature of the object

Josef Stefan, (1835 – 1893) Austrian physicist 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. 11/14/2015

Weins Law Most objects emit radiation at many wavelengths There is one wavelength where an object emits the largest amount of radiation max = 2897 (  m 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?

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. 11/14/2015

Temperature Scales Kelvin Celsius Fahrenheit Temperature Conversions: ºC = 5/9(ºF-32) K = ºC Absolute zero at 0 K is − °C (− °F)

11/14/2015 What are the similarities and differences between the Sun and Earth radiation curves?

11/14/2015 percentages in each wavelength band

11/14/2015 Radiative Equilibrium If the T of an object is constant with time, the object is in radiative equilibrium at T e What happens if energy input > energy output? What happens if energy input < energy output? Is the earth in radiative equilibrium?

11/14/2015 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?

11/14/2015 Radiative Equilibrium Temperature for the Earth Use Stefan-Boltzman Law Simplified case of no atmosphere T e = 255 Kelvin earth should be frozen! actual T e = 288 K

Earth emits 240 Watts m 2 Using E =  T e 4 then T e = (E/  ) 1/4 So, for the simplified case of no atmosphere T e = 255 K But T e = 288 K What is the reason for why the observed T e is warmer than what we calculated using the Stefan-Boltzman law??? 11/14/2015

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??? 11/14/2015

Earth – Range of primary wavelengths Sun – Range of primary wavelengths

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" 11/14/2015

Methane (CH 4 ) Carbon Dioxide (CO 2 ) Ozone (O 3 ) Water Vapor (H 2 O) Nitrous Oxide (N 2 O) 11/14/2015