for a copy of this presentation Climate Change Simple Serious Solvable Scott Denning Director of Education ESMEI Atmospheric Science CSU Simple 2 Serious 3 Solvable Simple 2 Serious ID: 777732
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Slide1
Email
Scott.Denning@ColoState.edu for a copy of this presentation
Climate Change:Simple, Serious, Solvable
Scott DenningDirector of Education, ESMEIAtmospheric Science, CSU
Slide2Simple
2. Serious3. Solvable
Slide3Simple
2. Serious3. Solvable
Slide4Heat Transfer
Conduction is by hot molecules colliding with neighbors
Convection is by hot stuff moving in bulk from place to place
Slide5Electromagnetic Radiation
Changing electric fields create changing magnetic fields …
and vice versa!
This makes energy move even through empty space
We can see it, feel it
Plants harvest it directly, and we harvest them!
Travels at 3x10
8
m/s
= 186,000 miles / sec !
Distance it goes in one cycle is called the wavelength
Slide6Electromagnetic Radiation
Radiation travels as waves or photons
Waves do not require molecules to propagate
Shorter waves carry more energy than longer ones
Slide7Blackbody Emission
Hot objects emit much more than cold objects at every wavelengthPeak emission at shorter waves at higher temperatures
Slide8Thermal ImagingImages taken in thermal infrared wavelengths (corrected for emissivity) produce accurate measurements of temperature
Slide9Solar
Emission
Solar radiation has peak intensities in the shorter wavelengths, dominant in the region we know as visible, but extends at low intensity into longwave regions.
Slide10Both are almost perfect blackbodies!
The hot sun radiates at shorter (visible) wavelengths that carry more energy
Energy absorbed by the cooler earth is then re-radiated at longer (thermal infrared) wavelengths
Thermal EmissionSUNEARTH
Slide1130% reflected by clouds, air, dust, and surface
19% absorbed by the atmosphere (mostly clouds)
51% absorbed at the surface
Solar Radiation
Slide12Molecules and PhotonsMolecules
are groups of atoms that share electrons (chemical bonds)Molecular transitions involve changes in vibration, rotation, bending, and stretching of chemical bondsPhotons can interact with molecules to change statesTransitions involve specific amounts of energy, so only certain wavelengths are activeMolecular transitions typically absorb & emit in thermal infrared
Slide13PhET Simulation
Slide14Dancing Molecules and Heat Rays!
Nearly all of the air is made of oxygen (O2) and nitrogen (N2) in which two atoms of the same element share electronsInfrared (heat) energy radiated up from the surface can be absorbed by these molecules, but not very wellN
N
OO
Diatomic molecules can vibrate back and forth like balls on a spring, but the ends are
identical
No electric dipole!
Slide15Dancing Molecules and Heat Rays!
Carbon dioxide (CO2) and water vapor (H2O) are different!They have many more ways to vibrate and rotate, so they are very good at absorbing and emitting infrared (heat) radiation
Molecules that have many ways to wiggle are called
“Greenhouse” moleculesO
O
C
H
H
O
Slide16CO2 Vibrations
15 mm7.2 mm4.3 mmC
CC
COO
O
O
O
O
O
O
Resting or ground state
No dipole … weak!
Temporary electric dipole … strong!
Slide17H2O Vibrations
Water molecules are “bent!”This gives them a positively charged end (with the hydrogen) and a negatively charged end (with the oxygen) This “permanent dipole moment” allows H2O to absorb & emit photons without moving bonds2.7 mm6.3 mm
Slide18Earth-Atmosphere Energy Balance
Earth's
surface absorbs the 51 units of shortwave and 96 more of
longwave energy units from atmospheric gases and clouds.These 147 units gained by earth are due to shortwave and longwave greenhouse gas absorption and emittance
.
Earth's surface loses these 147 units through convection, evaporation, and radiation.
Slide19Greenhouse Effect
CO2O3H2OH2
OHot surface emits directly to space in window regionCold upper layers emit to space in optically thick regionsTotal emission much less than from sfc
Slide20Bathtub AnalogyIf faucet runs faster than drain, level risesAnd vice versaDrain runs faster when water is deep
Adding glass to layer model acts like a clog in the drainWater rises until drainage = inflow againFaucet ~ SunDrain ~ Thermal emissionWater level ~ temperature
Slide21Slide228 PM surface temperature = 20 °C = 68
°F Spring Nightin Colorado
radiationemittedby soil
420 W m
-2
4 inches
= 10 cm
s
T
4
Slide23Spring Night
in Colorado8 AM surface temperature = -60 °C = -78 °F radiationemittedb
y soil
420 W m
-2
4 inches
= 10 cm
Slide246 AM surface temperature = 10 °C = 50
°F Spring Nightin Coloradoradiation
emittedby soil
420 W m
-2
4 inches
= 10 cm
radiation
emitted
by air
340 W m
-2
Slide25The strongest evidence for theGreenhouse Effect
is that we can survive night!
Slide26Common Sense
Doubling CO2 would add 4 watts to every square meter of the Earth, 24/7/365Doing that would make the surface warmerThis was known before light bulbs were invented!
4 Watts
1 m
1 m
John Tyndall, January 1863
Slide27Common Myth #1
“Scientists expect a warmer future because it’s been warming up recently”
WRONG! It’s because we know that when we add heat to things, they warm up
Slide28RememberHeat in minus heat out equals change of heat (“First Law Thermodynamics”)Earth can only exchange heat through electromagnetic radiation
Trace gases CO2 and H2O control rate of heat emission by EarthGreenhouse effect makes Earth habitable, allowed life to evolve