In Class Group Presentations on Jan 23
Modeling Global Warming
Remember doubling times and exponential growth!
Doubling time is 70/n; where n is the percentage growth rate. Thus
something which has a 5% rate of growth, doubles every 70/5 = 14 years.
Here is what we know.
- in 1900 the concentration of CO2 in our atmosphere was
280 parts per million.
- in 1900 the concentration of CH4 in our atmosphere was 1.2
parts per million
- The rate of increase of CO2 in our atmosphere is about 0.5%
per year over the last 100 years.
- The rate of increase of CH4 in our atmosphere is about 1.0%
per year but in the past 5 years seems to have declined to about 0.7%
per year (for unknown reasons).
Note that there is stored methane in artcic permafrost as well as gas
hydrate deposits in the ocean. As the oceans expand and warm, the
density of ocean water decreases and thus the pressure confinement by
the ocean layers of these gas hydrate deposits is relaxing, thus possibly
releasing large amount of methane.
Your task is to take the following set of input parameters and assumptions
and make a model prediction about what the effects of global warming will
be in 100 and in 200 years (i.e. in the year 2100 and the year 2200). You are to work together in your assigned team. Appoint a group
leader that will give a short (e.g. 10 minutes) in class presentation on the
results of your modeling.
There is no unique answer that you can get from this exercise. Your results
will be highly model dependent (which is the point of this exercise!).
Depending upon your assumptions, you might find that warming is severe
in which case you might want to spin your presentation towards that, or
you might find that its not as severe as the hype makes it sound.
Here is what we don't know and therefore must be modeled within some
parameter range. You should do some independent research to find the
best supporting scientific evidence for adopting various values below.
- The absorption of infrared radiation of CH4 relative to CO2
is uncertain and lies in the range of 10 to 25 times as much. (e.g. 1 CH4 molecule
is equivalent to 10-25 CO2 molecules). For instance, if this ratio is 10,
then in 1900 the combined CO2 + CH4 concentration in our atmosphere,
in units of CO2 ppm would have been 280 + 10*1.2 = 292. If this ratio is
25 it would be 280 + 25*1.2 = 310.
- A doubling of combined CO2 + CH4 will produce a net increase
in average global temperature of between 2 and 6 degrees C. This depends quite
a bit on the amount of water vapor feedback that will occur.
You should do a bit of research on this topic.
- The combined biomass on the planet currently can process 15 ppm of CO2
per year. The amount of biomass on the planet is shrinking in relation to population
growth at the rate of 1-3% per year. The Amazon rain forest accounts for 15% of the
worlds total biomass. However, global warming may actually grow more biomass
at high latitudes and so you can, if you can defend it, choose to actually
increase the amount of biomass per year.
- An increase in global temperature by each degree C will cause a rise in sea level of
between 0.25 and 0.75 meters. In addition, each increase by 0.5 degree C
will "suddenly" release methane from the frozen tundra. But the amount is
uncertain - estimates vary from 0.5 to 10 parts per million (its very
Thus, if the methane concentration
at Time X is say 20 ppm and 0.5 degree C increase has occurred then the
methane concentration will "suddenly" increase 20 ppm to somewhere in the
range 20.5 - 30 ppm. Again, you will need to incorporate this "sudden"
release factor directly into your model.
- The current world population growth is 1.5% per year and 1/3 of the world is
responsible for CO2 production (hence it grows at 0.5% per year).
Approximately 2/3 of the world is responsible for CH4 production.
If the LDC (less developed countries) use fossil fuels to reach the economic standard
of the developed countries, then these factors increase from 1/3 to 1 and from 2/3 to
Therefore your assumption matrix in this regard is the following:
a) The world will adopt the Kyoto protocol and cease to use fossil fuels as an
energy source and CO2 production will subside to zero over some
time scale and alternative energies will come into play.
b) Due to education and other stimuli, the world's population rate will continue to
decrease from 1.5% per year down to say 0.5% per year over the next 100 years.
c) The LDC will use fossil fuels and the rate of CO2 deposition will
increase up to some maximum value of say 1.5% per year.
d) A warmer climate will produce more biomass thus compensating by having a bigger
sink for CO2. Thus, you can choose to increase the biomass on the planet
with this assumption. This would be a positive feedback channel.
e) But, a warmer climate will melt the frozen methane as described above.
This would be a negative feedback channel.
Your task is to make a model, tied to a specific set of assumptions and give a report
- The assumptions you made in your model
- Your model predicted average temperature of the planet in 100 and 200 years
- The predicted sea level rise in 100 and 200 years
- Compare your model results from 1900 to 2000 with actual data
(you will have to do research to find data on sea level increase and
temperature increase, but its out there and relatively easy to find).
- The overall severity of this problem.
Again your team will need to do some independent research to see what some of the
"best" scientific estimates are for some of the parameter ranges specified above.
These presentations are due on Jan 21.1