1. Climate Change: Simple, Serious, Solvable
Scott Denning Director of Education, ESMEI Atmospheric Science, CSU
for a copy of this presentation

2. Simple 2. Serious 3. Solvable

3. Simple 2. Serious 3. Solvable

4. Heat Transfer Conduction is by hot molecules colliding with neighbors
Convection is by hot stuff moving in bulk from place to place

5. Electromagnetic 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 3x108 m/s
= 186,000 miles / sec !
Distance it goes in one cycle is called the wavelength

6. Electromagnetic Radiation
Radiation travels as waves or photons
Waves do not require molecules to propagate
Shorter waves carry more energy than longer ones

7. Blackbody Emission
Hot objects emit much more than cold objects at every wavelength
Peak emission at shorter waves at higher temperatures

8. Thermal Imaging
Images taken in thermal infrared wavelengths (corrected for emissivity) produce accurate measurements of temperature

9. Solar 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.

10. Thermal Emission SUN EARTH Both 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
SUN
EARTH

11. Solar Radiation 30% reflected by clouds, air, dust, and surface
19% absorbed by the atmosphere (mostly clouds)
51% absorbed at the surface

12. Molecules and Photons
Molecules are groups of atoms that share electrons (chemical bonds)
Molecular transitions involve changes in vibration, rotation, bending, and stretching of chemical bonds
Photons can interact with molecules to change states
Transitions involve specific amounts of energy, so only certain wavelengths are active
Molecular transitions typically absorb & emit in thermal infrared

13. PhET Simulation

14. Dancing Molecules and Heat Rays!
AT606 Fall 2006
3/13/2018
Dancing 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 electrons
Infrared (heat) energy radiated up from the surface can be absorbed by these molecules, but not very well N O
Diatomic molecules can vibrate back and forth like balls on a spring, but the ends are identical
No electric dipole!
CSU ATS Scott Denning

15. Dancing Molecules and Heat Rays!
AT606 Fall 2006
3/13/2018
Dancing 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 O C O O H H
Molecules that have many ways to wiggle are called “Greenhouse” molecules
CSU ATS Scott Denning

16. CO2 Vibrations O C O O C O O O C O C O 7.2 mm 15 mm 4.3 mm
Resting or ground state
CO2 Vibrations O C O
No dipole … weak!
7.2 mm O C O
15 mm O O C
Temporary electric dipole … strong!
4.3 mm O C O

17. H2O Vibrations Water molecules are “bent!”
2.7 mm
6.3 mm
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 bonds

18. Earth-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.

19. Greenhouse Effect Hot surface emits directly to space in window region
Cold upper layers emit to space in optically thick regions
Total emission much less than from sfc
CO2 O3
H2O

20. Bathtub Analogy If faucet runs faster than drain, level rises
And vice versa
Drain runs faster when water is deep
Adding glass to layer model acts like a clog in the drain
Water rises until drainage = inflow again
Faucet ~ Sun
Drain ~ Thermal emission
Water level ~ temperature

21. AT606 Fall 2006
3/13/2018
CSU ATS Scott Denning

22. Spring Night in Colorado
radiation emitted
by soil
420 W m-2
8 PM surface temperature = 20 °C = 68 °F
4 inches
= 10 cm
sT4

23. Spring Night in Colorado
radiation emitted
by soil
420 W m-2
8 AM surface temperature = -60 °C = -78 °F
4 inches
= 10 cm

24. Spring Night in Colorado
radiation emitted
by air
340 W m-2
radiation emitted
by soil
420 W m-2
6 AM surface temperature = 10 °C = 50 °F
4 inches
= 10 cm

25. The strongest evidence for the Greenhouse Effect
is that we can survive night!

26. Common Sense
John Tyndall, January 1863
4 Watts
1 m
Doubling CO2 would add 4 watts to every square meter of the Earth, 24/7/365
Doing that would make the surface warmer
This was known before light bulbs were invented!

27. Common 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

28. Remember
Heat 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 Earth
Greenhouse effect makes Earth habitable, allowed life to evolve