NSI Script Day 7
Journal Starters:
"Man, in the words of one astute biologist, 'is...faced with the problem of escaping from his own ingenuity.'" --Loren Eiseley
Record your initial impressions and thoughts about global warming, before you do any research.
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I'm going to give an overview of the next project, but then want to get you to dive right in to look at the data and the claims about global warming. So most of today we'll work informally, to help people with collecting global warming data, etc. I'm going to introduce you to the topic of global warming and then let you start your research on it.
Our atmosphere is basically a collection of gases that surrounds the planet, held in place by gravity. (compare to moon, for example, or Jupiter at other extreme- holds on to even light hydrogen - molecules are bouncing around, and would drift off into space if not held down by gravity) Earth's atmosphere is primarily made up of the following gases (percentages are by number of molecules):
0.03% C02
78% nitrogen
0.9% argon
21% oxygen
0.1-3.0% water vapor
75% of the mass of the atmosphere is found within about 7 miles of the surface, in a region called the troposphere. This is where weather (rain, clouds, snow, etc.) occurs.
(Our atmosphere does several important things for us: air to breath, protects from meteor shower, protects from cosmic rays, ozone protects from ultraviolet rays, greenhouse effect)
The greenhouse effect is NOT inherently a bad effect. In fact, it's necessary for our survival. If our atmosphere did not include any gases that cause the greenhouse effect, the average surface temperature of Earth would be -18 (-1.3 degrees F) or -19 degrees C, well below the freezing point of water. The greenhouse effect is responsible the fact that the Earth's average surface temperature is actually 14-15 degrees C (58 degrees F), a range hospitable to life.
To understand this, first imagine that earth had no atmosphere. What would determine its temperature in that case? Balance between sunlight received, and radiation rate. When very cold, it absorbs faster than radiates. But as it gets hotter, rate of radiation goes up. Eventually reach a balance, where incoming and outgoing rates are equal, and temperature stays roughly constant. Can increase balance temp by either: increasing heating rate (hotter, closer sun) or decreasing cooling rate --->
This is how the greenhouse effect works:
When radiant energy from the sun reaches our atmosphere, about 30% of it is reflected back into space by the atmosphere or the surface of the Earth, but about 75% of it is absorbed by the atmosphere or the surface of the Earth. As the Earth warms, it emits infrared radiation. This infrared radiation is absorbed by the greenhouse gases and reradiated in all directions, including back down to the Earth. (The atmosphere is pretty good at transmitting short wave lengths, but not long wavelengths. Analogy to spring or pendulum which has natural frequency) The overall effect is that you have more radiant energy striking the Earth and heating it up.
Greenhouse Gases:
1. carbon dioxide: released when fossile fuels are burned. Fossil fuels are the remains of animals that died hundreds of millions of years ago. When burned, the carbon in these materials combines with oxygen in the air to form CO2. (coal-burning electric power plants, cars). Plants remove about 3% of CO2 produced each year. Ocean absorbs about 25-45%. (CO2 dissolves well in water...think about soda drinks!) Increasing use of fossil fuels, burning and/or cutting down of rainforests, etc. makes situation worse.
2. methane: 20-30 times more effective than CO2. Produced by anaerobic bacteria that thrive in swamps, marshes, etc and in intestinal tracts of animials and insects. Rice fields, cattle, termites, etc. can produce a lot of methane. (Rice is main part of diet in some of the fastest growing nations, logging and burning leaves a lot of wood for termites to eat). Natural gas pipeline leaks can release methane in the air. Much methane is trapped in permanently frozen soil in the Arctic. Could have positive feedback here.
3. nitrous oxide: 200 times more effective than CO2. Produced in just about any combustion process. Also created when chemical fertilizers w/ nitrogen (in form of amonium nitrate) added to soil. (Bacteria in soil break down amonium nitrate.)
4. CFCs: chlorofluorocarbons-nontoxic and nonexplosive. Amazing number of applications. 10,000 times more effective than CO2. Stay around for a very long time. Also hurt ozone layer, which is important in filtering out ultraviolet radiation from the sun.(could elaborate on)
5. water vapor: amount in air increases as temperature increases. Low clouds might decrease greenhouse effect (by providing more reflection), high clouds might increase greenhouse effect, since water vapor is a greenhouse gas.
Historical Perspective:
temperature changes in the past
change in atmosphere due to anerobic creatures
(Earth and probably life will survive - there have been much more dramatic changes than anything we could likely do - so the issue is not about saving the earth, it's about not having dramatic consequences for human life:)
Possible Consequences:
agricultural disruptions--local climates might change considerably
tree migration--can't migrate quickly, like animals. Many forests might die off
more severe coastal storms--warming oceans can effect air patterns and jet streams
rising sea level (thermal expansion, melting glaciers and polar ice...polar caps are estimated to contain enough water to bring the oceans of the world up by about 250 ft)--cities flooded, peopele displaced, salt water contaminating drinking water, crops destroyed, etc.
higher temperatures effect on humans: health concerns, higher air pollution often accompany higher temperatures, more insects, unstable politics
Skeptic arguments:
computer models: stick in initial conditions and equations modeling all relevant processes...small changes in these can lead to big changes in the results. (activity without insight danger again)
Atmosphere divided into rectangular boxes, about 1 mile high and the size of Colorado. In each box, equations that represent flow of heat, moistire. wind, sunlight, etc. Boxes interact with adjacent boxes. Can be difficult to get good set of inital conditions across the globe (or to check predictions at a given time). Start w/ initial condition and let equations churn. Can tweak a parameter (like CO2 in air) and see what happens.
clouds
dust-dust in upper atmosphere can reflect sun's light. Most comes from volcanos. May cause only temporary cooling, but some suggest this is one of nature's long-tem cooling methods
ocean--good absorber of CO2. May be able to absorb higher concentrations of CO2 as the concentration increases in the air. (But warm water holds less CO2 than cold water.) CO2 rich water may stimulate growth of phytoplankton, which would take in more CO2 from air.
sunspots--dark spots on face of sun that are caused by magnetic storms. Radiation from sun increases during intense sunspot activitiy. Occur in overlapping cycles of different periods. Two overlapping peaks of sunspot activity could be reponsible for the higher temperatures seen in the last 100 years.
References for Lecture:
"The Greenhouse Effect" by Sharon Thompson--simple, short description.
"Is the Temperature Rising?" by S. George Philander
"Global Warming: Understanding the Forecast" by Andrew Revkin