NAME: _________________________________________________ QUIZ SECTION: ____________
ATMS 101 Autumn 2008
Homework #6 (Due Wednesday, November 19)
Please show all work and write neatly in the space provided.
Radiation and Energy
1. As objects increase in temperature:
a. What happens to the motion of the molecules of the object?
Motions increase (temperature is a measure of the average kinetic – or “movement”
– energy of the molecules).
b. What happens to the wavelength of the emitted radiation?
It decreases.
c. What happens to the intensity of the emitted radiation?
It increases.
2. Radiative equilibrium is a balance between the incoming and outgoing radiation.
Imagine that the Earth’s incoming radiation suddenly increased and in order to
reach radiative equilibrium again the Earth’s outgoing radiation also increased.
What would happen to the Earth’s temperature and why?
The Earth’s temperature would be warmer. With the sudden increase in the
amount of incoming radiation from the sun, a new radiative equilibrium had to be
established. The Earth warmed up until it reached a temperature where it emitted
an amount of energy equal to the new (increased) amount from the sun. Remember
(from question 1c) an object must warm to emit more radiation.
3. Roy is attending a bonfire before a football game. Name the type of heat transfer
(conduction, convection, or radiation) that causes each of the following and briefly
explain your answer. (Hint: two processes occur in one of these situations.)
a. Roy’s face warms as he stands next to the fire with his friends.
Radiation: the fire radiates heat directly and does not require a medium (such as a
fluid or direct contact) to transmit that heat.
b. Ashes above the fire rise into the air.
Convection: small air parcels are heated by the fire and become warmer than
surrounding air. These parcels rise and carry ashes with them.
c. Five minutes after a pot of water is placed on the fire, the water begins to boil.
1) Conduction: the pot is heated directly due to contact with coals (or something)
(and the water touching the pot is heated directly by the pot); 2) Convection: water
nearest to the pot heats up more than the surrounding water and rises, causing
circulation. Also: some of the liquid water is heated enough to become vapor and
rises through the water (boiling).
d. Roy’s tongue is burned when he sips his hot chocolate.
Conduction: Roy’s tongue is heated by direct contact with the hot liquid.
4. Fill in the following blanks with “solar”, “infrared”, or “neither”:
a. Clouds absorb and emit _____infrared_____ and reflect _____solar_____.
b. The Earth’s surface is nearly a blackbody, which means it absorbs _solar (we
accepted ‘solar’ and/or ‘infrared’) _ and emits _infrared (we accepted ‘solar’
and/or ‘infrared’)_ and it also reflects significant amounts of _____neither___.
[The reason we pointed out that it’s nearly a blackbody was to emphasize the fact
that a blackbody doesn’t reflect. However, because a blackbody – by definition – is ‘willing’
to absorb and emit at all wavelengths, we accepted ‘solar’ and/or ‘infrared’ for the first two
blanks. However, keep in mind the Earth does not emit solar radiation (it could only emit at
those short wavelengths if it was very hot, like the sun).]
c. Snow covered regions reflect ___solar___, which causes it to appear white.
Greenhouse Effect and Global Warming
5. a. What are the two most important greenhouse gases?
Water vapor and carbon dioxide.
b. What effect do greenhouse gases have on incoming solar radiation?
No effect: solar radiation is permitted to reach the Earth’s surface unimpeded such
that it directly heats the surface. (Some students pointed out that ozone can be a
greenhouse gas when it is in the troposphere, and that ozone also absorbs the UV
portion of the solar spectrum – we accepted this.)
c. Do you think that there would be any “greenhouse effect” if we were able to
suddenly get rid of all of the carbon dioxide in the atmosphere? Why / why not?
Yes: carbon dioxide is not the only gas that accounts for a greenhouse effect. There
are other greenhouse gases (notably: water vapor).
6. Greenhouse gases such as CO2, water vapor, and methane cause our atmosphere to be
warmer than it otherwise would be. What is different about these gases compared to
other atmospheric gases (such as O2, N2, Argon, and Neon) that are NOT greenhouse
gases?
Greenhouse gases absorb and re-emit far infrared radiation (which is emitted from
Earth).
7. Read p. 391 “Climate Change and Feedback Mechanisms” to answer the following:
a. If the Earth was in a global cooling period, explain how increased snowfall would
accelerate Earth’s cooling. Is this a positive or negative feedback?
Increased snowfall and increased snow cover would lead to an increase in Earth’s
solar reflectivity. This means that more of the sun’s radiation would be reflected
directly out to space and less of it would be absorbed as heat. This is a positive
feedback because the result of the feedback mechanism is to further the effect that is
already happening (i.e. increased snow is caused by cooler temperatures, which – in
turn – leads to even COOLER temperatures).
b. Explain how water vapor can have a (direct) positive feedback and (indirect)
negative feedback on global warming.
Direct positive feedback: warmer temperatures leads to an increase in the
amount of water vapor (through evaporation and higher dewpoint temperatures).
Because water vapor is a greenhouse gas, this would contribute to the warming.
Indirect negative feedback: Increased water vapor can lead to increased low
clouds. An increase in clouds means more of the solar radiation is reflected out to
space instead of absorbed by Earth as heat.