Family Homecoming Special Event

"Can Climate Engineering Serve as a Complementary Step to Aggressive Mitigation?"

¨Dr. Michael MacCracken, The Climate Institute, Washington, DC

¨Friday, Sept. 25 at 4:00 pm in Olin 1, with cookies

Hydrologic Cycle

Annual Precipitation, Washington

State

The Atmosphere’s Energy

Read Anthes chapter 3

Energy is the ability to do work

Units are mass x distance2 / time2

Potential energy: E = mgh

Kinetic energy: E = 1/2 mv2

Heat energy: sensible and latent

Radiant energy: visible and infrared

Laws of Thermodynamics

1. Conservation of energy: Energy is neither created nor destroyed; it is transformed. you can't take out of a system more than you put in.you can't win

2. The entropy of the universe is continually increasing. perpetual motion and a heat engine with 100% efficiency are both impossible.you can't break even

3. It is impossible to attain absolute zero or absolute 0 entropy. you can't even get out of the game

Energy transformation example:Hydroelectric power plant

More complete picture:

Solar power (drives hydrologic cycle)

Potential energy (water stored in reservoir)

Kinetic energy (spillway)

Mechanical energy (spinning turbines)

Electrical energy (transmitted over wires)

Lightbulbs (converts energy to light)

Waste heat (IR) is lost to space

Transfer of Energy

Conduction -- Molecular motion

Convection -- Mass transfer vertical

Advection -- Mass transfer horizontal

Latent heat -- Ice and liquid phases

Radiation -- SW and LW photons

Conduction (molecular motion)

Thermal conductivity is the ability of a substance to transfer heat via molecular motion.

Measured in units of cal/sec/cm/oC

Conductivity of solids > liquids > gases.

Silver (good conductor) = 1.0

Water (1000 times worse) = 1.4 x 10-3

Ice = 5.3 x 10-3

Air (good insulator) = 6.1 x 10-5

Convection and Advection (mass transfer)

Rising air currents (thermals) carry sensible heat and latent heat from the surface into the upper air.

Winds (advection) carry sensible heat and latent heat (moisture) into northern latitudes.

Ocean currents transfer warmer waters to northern latitudes and vice-versa.

The Electromagnetic Radiation

Every object in the universe emits radiation.

From 1012 cm radio waves to 10-12 cm gamma rays

Stefan-Boltzmann Law

Hotter bodies emit more total energy than colder bodies.

The total energy of a blackbody is proportional to the fourth power of temperature.

Etot = T4

Compare energy emitted by Sun and Earth

Energy emitted per unit of surface area:

E / E = T4 / T4

= (6000 / 300)4 = 204 = 1.6 x 105

Energy emitted by the entire surface

Multiply by R2/ R2

= (100/1)2 = 104

So Sun emits 1.6 x 109 more energy than Earth

Power in wattsSun 3.6 × 1026

Total human consumption, global 1.3 × 1013

Total human consumption, US 3.2 × 1012

Large commercial power plant 109 to 1010

human, daily average from diet 100 (one light bulb)

per capita world 2 x 103 (20 lightbulbs)

per capita US 104 (100 lightbulbs)

Planck energy distribution curve (energy density per unit time per unit wavelength)

Wein’s LawThe wavelength of maximum emission depends

inversely on a body’s Kelvin temperature.

max = 2897/T (microns)

Emission from hotter bodies peaks at shorter wavelengths.

What is max for the Sun?

max = C/T = 2897/ 6000 = 0.48 microns = yellow visible light

What is max for the Earth?

max = C/T = 2897/ 300 = 10,1 microns = infrared

Trace gases absorb radiation at selected wavelenghts.Atmosphere is transparent to sunlight at 0.5m and to IR at 10m

Net result

Make a heat budget at the top and bottom of the atmosphere

\Top of atmosphere: Gains = Losses 100 SW - 31.3 SW - 68.7 LW = 0

Surface: 7.6 SW + 43.2 SW + 98 LW - 7.6 SW - 4.4 C - 22.8 E - 114 LW = 0

This is the average balance sheet -- Dynamic balance is never achieved!