You are expected to submit a summary of a current climate / environmental-related article from the mainstream press, along with your

Account for the Greenhouse Effect (one layer atmosphere model)

σTs 4 =

S 4 1− Albedo( )+σTe

4

σTs 4 = 2σTe

4

σTe 4 =

S 4 1− Albedo( )

Ts = 2 1 4Te240 Wm-2 coming into surface

240 Wm-2 leaving into space

340 Wm-2 available before accounting for albedo

*Remember S is the solar constant 1365Wm2

Ts is earth surface temp. Te is temp at the top of the atmosphere where energy is radiated back to space

1)

2)

3)

4)

Here is our one layer atmosphere model that we reviewed previous week. Although this is a great model to help us learn how a climate model works, it is a little too simple to represent our true atmosphere.

Can you think about what is unrealistic about this layer model? Although there are a number of answers, what stands out most in terms of the greenhouse effect is that 1) not all atmospheric gases are greenhouse gases; and 2) the temperature of the atmosphere is not vertically homogenous.

1) Not all atmospheric gases are greenhouse gases. This layer model is based upon a simple concept of “what goes in, must come out”. With this, in the second equation, the Earth’s back radiation is completely absorbed by the atmosphere (greenhouse gases) and radiated equally back to the surface of Earth and to space (equation 2, in slide). However, in reality, we all know that greenhouse gases are definitely not a major component of the atmosphere! This week, let’s talk about what make greenhouse gases – greenhouse gases! After this week, you should be able to explain “what are greenhouse gases” from a slightly different perspective – in a quantum mechanical way.

2) temperature of the atmosphere is not vertically homogenous. Of course, when you are away from a heat source (in this case, the surface of the Earth), temperature decreases. However, such diffusion cannot be expressed by a simple layer model. Therefore, climate scientists combine multiple layer models vertically and horizontally to make a climate model close to reality.

Composition of the Atmosphere including variable components (by volume)

As we learned in previous lectures, major composition of the atmosphere is nitrogen, oxygen, and argon. Very interestingly, greenhouse gases consist of only a fraction of the atmosphere, and are called trace gases.

Radiative forcings, IPCC 2013

That said, although small, these gases are important in altering the Earth’s energy budget. Based on the IPCC’s (Intergovernmental Panel on Climate Change) assessment report (IPCC 2007), greenhouse gases, such as CO2, CH4, N2O, and Halocarbons, show positive radiative forcing. This means that these gases contribute to warming of the atmosphere.

CO2 carbon dioxide CH4 methane

N2O nitrous oxide

Important to note that, although we are focusing on CO2 to examine climate sensitivity here, we all know that there are other molecules that can absorb long wave back radiation: water molecules (H2O), methane (CH4), nitrous oxide (N2O), etc.

Elements Atoms

Nucleus Protons (+) Neutrons (o)

Electrons (-)

• All matter, including minerals, rocks, and gas molecules, are made of atoms

The chemical composition First, let’s review basic chemistry.

Atoms

• Smallest particle into which an element can be divided while still retaining the chemical characteristics of that element

Here is an example of an oxygen atom. This conceptualized view is only an approximation or model showing the nucleus of the atom surrounded by orbiting electrons (middle figure). A more realistic view consists of electron shells surrounding the nucleus. Electrons are in the probability clouds (far right figure). This expression is based on quantum mechanics.

Carbon atom

Electron cloud

Nucleus

Composed of a nucleus surrounded by electrons Nucleus is composed of protons (+) and neutrons (0)

Carbon atom

Electron cloud

Nucleus

Carbon has 6 electrons…

Electron (–)

Proton (+) Neutron

Number of neutron adds mass to the atom.

Number of electrons (-) orbiting nucleus determined by the number of positively charged protons.

Negatively charged electrons balance the positive charges of the protons.

Carbon atom

Electron cloud

Nucleus

Carbon has 6 electrons…

…and a nucleus of 6 protons …

…and 6 neutrons.

Electron (–)

Proton (+) Neutron

Number of protons defines the chemical element and atomic number (e.g. atomic number of hydrogen (H) is 1, He is 2, Li is 3, …)

ION = Charged Particle

CATION = Positive Charge (lose electrons, i.e., Fe+2)

ANION = Negative Charge (gain electrons, i.e., O-2)

BONDING Each atom may or may not be connected to other atoms

with different types of bonding. Here, we learn three major bondings: ionic bond, covalent bond, and

hydrogen bond.

Sodium atom Chlorine atom

Ionic Bond Here is an example of NaCl, also know as salt.

Sodium loses one electron… …and chlorine acquires it.

Electrical attraction

Sodium atom Chlorine atom Cation (+) Anion (–)

Ionic Bond Sodium and chlorine are attracted to each other and create ionic bonding.

Carbon atoms are arranged in regular tetrahedra…

…that share electrons with neighboring atoms.

Carbon atoms Electrons

Nucleus

Covalent Bond

Covalent bond is one of the strongest bonds. In this type of bonding, the atoms share an electron with adjacent atoms, so they are not easily separable. Examples of covalent bonds are ozone (O3), hydrogen (H2), water (H2O), methane (CH4), ammonia (NH3), and CO2 (carbon dioxide).

The Hydrogen Bond • Chemistry of water

– Atoms and molecules – Two hydrogen and one oxygen molecule (H2O) – Covalent bonds – Electrical polarity

of water molecule – Hydrogen bonds

The hydrogen bond is a unique and weak bond. It is the electrostatic attraction

between two polarized groups of atoms/molecules. One most famous example is a water molecule. Although, as we saw in the previous slide that a water

molecule is a covalent bond, the bonds connecting water molecules are

hydrogen bonds. This occurs because the molecular structure of water is

unique and naturally polarized (electronically imbalanced) – I call this

molecular structure a Mickey Mouse structure! Because water molecules are polarized, each molecule is attracted electrostatically. Therefore, water has a

wonderful surface tension. In our childhood, we all tried to put as many water

drops as possible on a surface of the coin… We are able to do this because of

the hydrogen bond.

Okay – let’s continue to learn about greenhouse gases in the following lecture

slides.

http://www.ces.fau.edu/nasa/mod ule-2/how-greenhouse-effect- works.php

This figure shows the blackbody spectra of Earth and sun. The incoming radiation from the sun is much more intense (Y-axis) than that of outgoing radiation from the Earth because the energy emitted from a blackbody is proportionate to its temperature to the fourth (σT4) – i.e. the sun emits a far greater amount of energy than the Earth. Incoming solar radiation is shortwave (X-axis, wavelength in microns) and in the wavelength range of ultraviolet and visible radiation (shown as the rainbow spectrum of colors). Outgoing Earth’s radiation is long wave and and is in the range of infrared radiation (shown in red).

Below the blackbody spectra, molecules in the atmosphere, known as greenhouse gases, interfere with incoming and outgoing radiation. For instance, ozone (O3) in the stratosphere absorbs some of incoming radiation and is known as the ozone layer. That said, greenhouse gases (N2O, O3, CO2, and H2O) mainly interfere with outgoing radiation.

Let’s talk about the molecular motion of these greenhouse gases to understand the greenhouse effect.

Molecular Motions and the Greenhouse Gases H2O and CO2

2349cm-1 667cm-1

Here are the physical causes (molecular motion) of the greenhouse effect. But first… it may be a bit chunky, so sit back, take a deep breath!

Gas molecules can absorb or emit radiation in the infrared range in two different ways. One way is by changing the rate at which the molecules rotate. The theory of quantum mechanics describes the behavior of matter on a microscopic scale – that is, the size of molecules and smaller. According to this theory, molecules can rotate only at certain discrete frequencies as if vibrations of a piano string in that they tend to be at specific “ringing” frequencies. (The rotation frequency is the number of revolutions that a molecule completes per second.) The molecule can absorb incident wave (energy), if this incident wave has just the right frequency.

This frequency of the radiation that can be absorbed or emitted depends on the molecule’s structure. The H2O molecule is constructed in such a manner that it absorbs infrared radiation of wavelengths of about 12 micrometers and longer. This interaction gives rise to a very strong absorption feature in Earth’s atmosphere called the H2O rotation band. As shown in the previous slide, virtually 100 % of infrared radiation longer than 12 micrometers is absorbed with a combination of CO2 and H2O.

(By the way, the H2O rotation band extends all the way into the microwave region of the electromagnetic spectrum, i.e. above a wavelength of 1000 micrometer, which is why a microwave oven is able to heat up anything that contains water.)

Molecular Motions and the Greenhouse Gases H2O and CO2

2349cm-1 667cm-1

The second way in which molecules can absorb or emit infrared radiation is by changing the amplitude at which they vibrate. Molecules not only rotate, they also vibrate – their constituent atoms move toward and away from each other. As shown in the lower figures, The molecular structure of water is electrically lopsided; a molecule is bent to its lowest energy state. This is because oxygen has two pairs of electrons hanging off it, which push the hydrogen toward the other side (Mickey Mouse structure!). Hydrogen atoms hold their electrons more loosely than oxygen atoms in chemical bonds, so each hydrogen has a slightly positive charge. The oxygen end of the molecule has a slight negative charge. Thus, water has a dipole moment built into its resting structure. Rotating an H2O molecule would oscillate the electric field and generate light. Due to the complex arrangement of the nuclei in H2O, there are many modes of vibration for the water molecule, including a symmetric stretch and a bend.

The CO2 molecule can vibrate in three ways. The bending mode of vibration (upper figure). This vibration has a frequency that allows the molecule to absorb infrared radiation at a wavelength of about 15 micrometers, which gives rise to a strong absorption feature in Earth’s atmosphere called the 15-micrometer CO2 band. Also, similar to a H2O molecule, the oxygen of a CO2 molecule tends to pull on electrons more tightly than carbon does, but the oxygen atom on one side pulls the electrons just as tightly as the other oxygen on the other side. Therefore, the molecule has no permanent electrical field asymmetry (dipole moment). This imbalance makes CO2 an important one for our climate. In fact, most gases in the atmosphere do not absorb or emit infrared light at all (e.g. N2). Why? Because vibrations in their bonds do not create an imbalance in the electrical field.

Molecular Motions and the Greenhouse Gases H2O and CO2

2349cm-1 667cm-1

What does all of this information mean? Your take home note is…. in order for gas molecules to interfere with electromagnetic energy (to emit or absorb infrared light); 1) frequency of the molecular vibration must be equal to the frequency of the

light (only a specific frequency of light can cause a specific molecular vibration!), and

2) the molecule must be electronically lopsided.

I am sharing a Youtube video that is very well made and that allows us to visually perceive these molecular motions. Please see a following slide.

Youtube video – https://youtu.be/3ojaDMadZXU

Please view this Youtube video to further your understanding of molecular motion. Particularly, the part from 2:40 to 4:47 is relevant to this lecture.

NASA, Robert Rohde – http://earthobservatory.nasa.gov/Features/EnergyBalance/page7.php en:NASA Earth Observatory

Atmospheric gases only absorb some wavelengths of energy but are transparent to others. The absorption patterns of water vapor (blue peaks) and carbon dioxide (pink peaks) overlap in some wavelengths. Water vapor is naturally electrically lopsided and can absorb and emit lots of frequencies of infrared light. Interesting about H2O is that not only is it a greenhouse gas, when we increase the surface temperature, more water will evaporate, which significantly increase the amount of water vapor in the atmosphere. Interestingly, this then makes H2O the most concerning greenhouse gas with greater uncertainty.

Carbon dioxide is not as strong a greenhouse gas when compared to water vapor, but it absorbs energy in wavelengths (12-15 micrometers) that water vapor does not. This is an important wavelength range because it is close to the peak intensity of outgoing radiation (thus effectively absorbs outgoing energy).

(Illustration NASA, Robert Rohde)

https://cimss.ssec.wisc.edu/sage/meteorology/lesson1/AtmAbsorbtion.htm

Atmospheric Absorption of incoming shortwave and outgoing longwave radiation

Total atmospheric absorption is indicated by the bottom row. The white areas indicate regions of the electromagnetic spectrum not affected (low absorption) by the atmosphere where solar radiation can reach the Earth's surface and terrestrial radiation can escape out to space. Note the prominent role that water vapor has in absorbing Earth's long wave radiation.

Outgoing spectrum of the Earth With an atmosphere

Okay – this is the last figure of today’s lecture.

In this figure, smooth curves show blackbody spectra for temperatures ranging from 300 K, surface temperature on a hot summer day, down to 220 K, which is about the coldest it gets in the atmosphere, up near the troposphere at about 10- km altitude. There is also a jagged-looking curve (denoted as “Atmosphere”) moving among the smooth ones. This is a model-generated spectrum of the infrared light escaping to space at the top of the atmosphere. This is jagged- looking because CO2, water vapor, ozone, and methane absorb specific wavelengths of outgoing energy emitted from the ground.

So, what would the Earth’s surface temperature look like from space if the Earth had no atmosphere? – Without an atmosphere, more energy will be radiated due to a lack in the greenhouse effect. In fact, the outgoing spectrum will look like a blackbody spectrum for 270 K (= -3 C�, 26.6 F), between the 260 K and 280 K spectra shown in figure. Compare this with the mean surface temperature described in slide #12. Blackbody spectra of Earth temperature is 255 K!

August, 2016 https://eos.org/research- spotlights/which-greenhouse-gas-does- the-most-damage-to-crops