Tue., Aug. 29, 2006

The Experiment #1 materials were handed out at the beginning of class today.  Start the experiment at a time when you will be able to check it every few hours for part of the day (once it is underway it will slow down and you will not need to monitor it so frequently).  Once you have collected all of your data, return the materials and pick up the supplementary information sheet.  If you weren't able to check out the materials today, there may be a few extra kits still available on Thursday.

The first 1S1P Report assignment was made in class today. You can choose from 4 topics.  You can write one or two reports (or no reports at all, though you won't receive any credit in that case and your grade might ultimately suffer).  Reports are due at the beginning of class on Monday Sept. 11.  Be sure to review the rules governing 1S1P reports.

I forgot to show the forecast path of Tropical Storm Ernesto issued by the National Hurricane Center.  Ernesto is now expected to travel northward along a large portion of the east coast of Florida.  Ernesto is predicted to pass very close to the Kennedy Space Center and NASA may move the space shuttle from the launch pad back into the Vehicle Assembly Building for protection.  Meanwhile, in the Pacific, tropical storm John is forecast to pass close to the southern tip of Baja California where it could move moisture up into our area and influence our weather by the end of the week.
Last week we saw that combustion of fossil fuels and deforestation were causing the atmospheric concentration of carbon dioxide to increase.  This in turn might be the cause of a 0.7o to 0.8o C increase in global annual average surface temperature that has observed over the past 150 years or so.

Today we looked very briefly at some of the natural changes in climate that have occurred on the earth.

You might be surprised to learn that the earth is currently in an ice age, one that began about 2 million years ago.  This is one of several ice ages thought to have occurred in the past (the figure above is on p. 5 in the photocopied class notes).  Ice is found at the N. and S. Poles during these ice ages.  The poles were ice free during the long periods in between ice ages.  Some scientists believe the earth's oceans froze over completely during the coldest ice ages; the name "snowball earth" is used to describe this occurrence.


We are actually living in a relatively warm part of the current ice age.  These warm periods are called interglacial periods.  In between are colder glacial periods.  The most recent glacial period ended about 20,000 years ago.  1 or 2 mile thick ice sheets covered portions of the norther U.S. during the last glacial period.  An ice sheet animation shows the shrinkage of the ice sheets at the end of the last glacial period.

Changes in the shape of the earth's orbit around the sun and changes in the direction and amount of tilt of the earth are though to be the cause of the climatic changes shown in the figure above.  Note there is almost a 10o C difference in temperature between the warmest and coldest periods.



The figure above shows the changes in temperature that occurred as the earth moved from the most recent glacial period into the current interglacial period.  The Younger Dryas event identified above was a large and sudden drop in temperatures that interrupted the warming.  Scientists are very interested in abrupt and somewhat unexpected changes like this.  The warm up at the end of the Younger Dryas period took only 40 to 50 years, a very sudden change in climate.  Note the Holocene maximum, roughly 5000 years ago, coincides roughly with the appearance of cities and the beginning of agriculture.


During a shorter warm period, the medieval climatic optimum, the Vikings established colonies in New Foundland.  These colonies were abandoned when the climate began to cool and Europe entered a period known as the Little Ice Age.

Larger volcanic eruptions, like the Tambora volcano mentioned above, can sometimes cause a short duration change in climate.  These eruptions send small particulates into the stable stratosphere where they can reflect incoming sunlight.  Probably the best recent example is the Mt. Pinatubo eruption in June 1991.  This caused the global annual average surface temperature to cool about 0.5oC.  See pps 387 & 389 in the 4th ed. of the text (p. 385 in the 3rd ed.).
Next we looked at some predictions for the next 100 years.

Scientists use computer models to predict future climate.  They incorporate mathematical descriptions of the atmosphere and atmospheric processes into their models.  They must also make assumptions about how human population will grow in the future and how people will use energy.

The curves in the next 4 figures assume that there will be rapid growth of the world economy, that global population will peak in mid century and will begin to decline thereafter, and that new and efficient technologies will be adopted quickly by the world economy. 

Three assumptions are made concerning energy sources.  The first (curve A1F1) assumes that fossil fuels will supply most of the energy needs throughout the period.  You can see (orange curve) in the first figure below that CO2 emissions are then predicted to grow throughout most of the next century.  A much better scenario (curve A1T in blue) would be to assume that a quick switch to alternative sources of energy is made.  In this case CO2 emissions peak fairly early in the next century and then begin to decrease.  The yellow curve lies between these two extremes.

 A1F1 - Fossil fuel intensive (in orange and a "worst case" scenario)
A1B - balance of all energy sources (yellow)
A1T - non fossil fuel energy sources (in blue and a "best case" situation)




CO2 concentration is now about 375 ppm.  The figure above shows CO2 concentrations in 2100 given the three scenarios above.
In the worst case scenario CO2 concentration would increase to more than 900 ppm.  In the best case situation CO2 concentration would increase to about 500 ppm.

Global average surface temperatures would increase 2.5o to about 4.5o C by 2100 depending on the fuel usage scenario.  Some regions would warm more than this, others less.  The figure below shows the 0.3 to 0.5 m expected rise in sea level that would occur as temperatures began to rise and ice sheets and glaciers began to melt.


Note that the rising in sea level is still headed upward at the end of this period.  The melting of the ice starts slowly.  Once it gets started it will then continue for some time even once the warming stops.

That will end our brief coverage of climate change.  We will learn much more about how the greenhouse effect works when we get to Chapter 2 in the text.  Three of the four 1S1P Assignment #1 topics cover different aspects of climate.  You can read more about natural changes in climate in Topic #2, the causes of natural climatic changes in Topic #3, and the possible consequences of global warming in Topic #4.

The four figures above are from  "Climate Change 2001: The Scientific Basis," published by the Intergovernmental Panel on Climate Change.  This and other reports is available online at www.ipcc.ch
At this point we took a brief detour and had a look at Experiment #1.

With this and the other experiments you will receive most or all of the materials you need to complete the experiment, a description of what should go into your report, instructions that tell you how to perform the experiment, and a data collection sheet.

The object of Experiment #1 is to measure the percentage concentration of the oxygen in air.  Basically you moisten a piece of steel wool, stick the steel wool into a graduated cylinder, and turn the cylinder upside down and immerse the open end in a cup of water.

As the next figure shows you need to use a small piece of flexible tubing so that water enters part way into the cylinder so that the water level can be read on the cylinder scale.



Be sure to remove the tubing once the water level can be read on the cylinder scale.  The air sample in the cylinder is now sealed off from the rest of the atmosphere.  The oxygen in the air sample will react with the steel wool to form rust.  As oxygen is removed from the air sample, the air sample volume changes.



The reaction between the oxygen and the steel wool sometimes happens in a day or two.  Other times it may take several days.  You will periodically need to record the time and the air sample volume ( you read the water level on the cylinder scale).  Be sure you do not lift the open end of the cylinder out of the water.  That would break the seal and you would need to restart the experiment.

Eventually the air sample volume will stop changing; all of the oxygen has been removed from the air sample and the experiment is over.
You will receive a supplementary information sheet when you have returned your materials.  You don't have to return the rusty piece of steel wool - throw it away.  Don't worry about trying to clean the rust stains off the inside of the cylinder.

We next began our coverage of three of the main air pollutants.  You'll find lots of detailed information about pollutants in Tucson and Pima County at the Pima County Department of Environmental Quality webpage.  The US Environmental Protection Agency also has a large amount of information about this topic.

We'll start with sulfur dioxide and finish up with carbon monoxide and ozone in our next class.



Sulfur dioxide is produced by the combustion of sulfur containing fuels such as coal.  Combustion of fuel also produces carbon dioxide and carbon monoxide.  People probably first became aware of sulfur dioxide because it has an unpleasant smell.  Carbon dioxide and carbon monoxide are odorless.


 The Great London smog is still the deadliest air pollution event in history.  A stable air layer next to the ground can't mix with cleaner air above. 

Acid rain often falls hundreds or thousands of miles away from the source of the SO2.  Coal fired factories and electric power plants in the Ohio River Valley could produce acid rain in New England and Canada.  Acid rain in Scandinavia could be the result of SO2 emissions in England and Belgium.


An acid rain demonstration was performed in the last 15 minutes of class to give you a general idea of how acid rain is produced.  Carbon dioxide rather than SO2 was bubbled through Tucson tap water.  The tap water is initially slightly basic (pH > 7).  Dissolved CO2 however turned the tap water acidic.