EPS219 – Energy and the Environment
Homework#6 – Due in class, Thursday, February 28, 2013
1) (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/
2) (10 pts) Ch9, #1: Why does deforestation contribute to global warming?
3) (10 pts) Ch9, #3: If the temperature on Earth rises enough so that the polar
ice caps begin to melt, would this melting cause the global temperature to
remain the same, drop, or rise higher? Why? (Consider feedback mechanisms.)
4) (10 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)
5) (10 pts) Explain how the fact that the energy radiated from an object
increases with temperature (by the 4th power) has a very stabilizing effect on
Earth’s surface temperature, given variations in solar output.
Because if the amount of incoming solar radiation changes up or down, there are
only very small changes in Earth’s surface temperature that are needed to
balance it (by emitting radiation that matches the incoming radiation) – i.e.,
small changes in surface temperature lead to large changes in solar radiation
output.
6) (10 pts) How can it be that volcanic eruptions can both increase global
temperatures and decrease global temperatures?
Over the long term, volcanic activity puts carbon dioxide into the atmosphere
which increases the greenhouse effect and increases global temperatures.
In the short term, a volcanic eruption can put aerosols and ash into the
atmosphere that can block out sunlight and decrease global temperatures.
7) (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 oxygen18/oxygen-16 isotope ratios?
Fossil shells are made of CaCO3, so they store away the oxygen at the time they
lived.
Evaporation from the ocean surface is mostly O-16, because it is lighter than O18.
Rain and snow is therefore mostly O-16.
During an Ice Age, the accumulation of ice on land (O-16) means that the ocean
becomes relatively enriched in O-18.
So, looking at ratios of O-18/O-16 can tell you when there is an Ice Age (the ratio
is high).
8) (15 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.
During the daytime, clouds block out sunlight and have a cooling effect.
During the nighttime, clouds (water vapor) absorb radiation leaving Earth’s
surface and have a warming effect.
Airplanes make contrails in the atmosphere – the ones at nighttime add to global
warming, but not the ones during the daytime.