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

Simple 2. Serious 3. Solvable

Simple 2. Serious 3. Solvable

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

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

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

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

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

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.

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

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

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

PhET Simulation

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

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

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

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

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.

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

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

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

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

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

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

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

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!

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

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