EPS219 – Energy and the Environment
Homework#6 – Due in class, Tuesday, March 3, 2015
1) (10 pts) The greenhouse effect involves feedbacks such as the way a global
increase in atmospheric carbon dioxide leads to an increase in Earth’s surface
temperatures. Explain why this is not the case with the correlation between
changes in atmospheric carbon dioxide and Earth’s surface temperature during
Ice Age cycles.
In this case, the temperature changes first in response to the Milankovitch cycles
of orbital parameters and then the carbon dioxide levels change in response.
2) (20 pts) Choose two different carbon footprint calculators and determine
your own carbon footprint, in metric tons of carbon per year. Choose from
among these sites, or find your own. You can do an individual or household
calculation. Please do a screen capture of the final page for both. Were the two
numbers similar? How did your carbon footprint compare to the average
American’s?
http://www.nature.org/greenliving/carboncalculator/index.htm
http://www.carbonfootprint.com/calculator.aspx
http://www.epa.gov/climatechange/ghgemissions/ind-calculator.html
http://www.footprintnetwork.org/en/index.php/GFN/page/calculators/
[Answers will vary. Full credit if they show screen captures of two different
calculators and have a few words answering the questions.]
3) (10 pts) Ch9, #1: Why does deforestation contribute to global warming?
Forest plants absorb CO2. If you cut the forests down, some of that CO2 gets
returned to the atmosphere when the dead tree decays. [or, the trees can no
longer absorb CO2 out of the atmosphere]
4) (15 pts) Ch9, #13: How much CO2 is produced by driving 100 miles, drying a
load of clothes, and watching five hours of television? (See Tables 9.4 and 10.2)
a) Driving 100 miles: At 20 mpg, adds 100 lbs of CO2.
b) load of clothes: about 5 lbs per load (5000W for 30 minutes)
c) 5 hrs of TV: 1 lb of CO2 (at 100W).
[anything roughly close gets full credit]
5) (10 pts) How can it be that volcanic eruptions can both increase global
temperatures in the long term and decrease global temperatures in the short
term?
Short term: sulfur dioxide aerosols block out sunlight, reducing the amount of
sunlight reaching Earth’s surface
Long term: increases CO2 content in atmosphere, adding to greenhouse effect
6) (15 pts) The figure showed in class for the very long-scale temperature
variations used ratios of oxygen-18 isotopes to oxygen-16 isotopes, taken from
fossil marine shells (which are largely calcium carbonate – CaCO3), as a proxy for
hot and cold periods. Research on the web how this works. In other words, why
are periods of Ice Ages associated with higher than normal oxygen-18/oxygen16 isotope ratios?
Most oxygen isotopes are in the form of O-16, but a small portion has two extra
neutrons and is in the form of O-18. When water evaporates off of the surface of
the ocean, the heavier O-18 preferentially stays behind in the ocean. That means
that the oxygen in rainwater is mostly O-16. So, when ice builds up on land
during an Ice Age, the ocean water gets enriched in O-18 isotopes. Ocean shells
(made of calcium carbonate – CaCO3) that form during these times of Ice Ages
therefore have a disproportionately high percentage of O-18 isotopes.
7) (10 pts) Explain why clouds have a reducing effect on Earth’s surface
temperatures during the daytime but an increasing effect at nighttime. Explain
why moving all airplane flights to the daytime and eliminating nighttime flights
would help reduce global warming.
Clouds have a warming effect on the atmosphere by absorbing energy radiated
up from Earth’s surface, trapping it in as part of the greenhouse effect.
During the day, some sunlight gets reflected off of the tops of clouds, having a
slight cooling affect on the atmosphere.
During the night, the clouds only have a warming effect.
Planes make contrails (clouds), and if they are during the day, then some of the
warming effect is counteracted by the cooling from sunlight reflecting off of the
tops of clouds.
8) (10 pts) Read the following short news items:
http://www.reuters.com/article/2015/02/15/us-canada-derailmentidUSKBN0LJ0S920150215
http://www.reuters.com/article/2015/02/17/us-usa-train-derailment-csxidUSKBN0LK1ST20150217
Explain how this might be an argument in favor of the Keystone XL pipeline.
Transporting oil via trains is dangerous and leads to multiple spills, as seen by
the recent accidents. A pipeline would be less likely to spill than trains.