Global Warming & Alternative Fuels : Part III
Previously I have written two blogs that have attempted to explain/understand why there is a need for Alternative Fuels and what where some of the pros and cons of each of the different technologies. The first blog was titled What Will be Powering Our Cars in the Future? and the second was called Alternative Forms of Energy : Part II in which I was a co-author with allpar member jstwe314.
In the third installment was this series I thought it would be interesting to discuss the ideas behind Global Warming. The reason being that Global Warming, along with many other issues such as money and terrorism to name a few, has driven the market to develop new technologies to combat the threat of Global Warming. Technologies such as the use of Ethanol, Hydrogen, Turbines, Fuel Cells to power our cars along with Wind, Hydro-electric, Solar Power sources.
To warn you ahead of time, no conclusions will be made by the end of the blog, neither a pro-Global Warming statement or against the idea of Global Warming. I don’t believe that I have the needed background to make such a conclusive statement for either side of the argument. Hopefully this blog will give you the reader some insights into the topic such that the reader may make his/her own judgment on the issue.
Before we get into the debate on whether Global Warming is real or not let us try and estimate what the temperature of the Earth would be if the Earth was only heated by solar radiation. To accomplish this task we must use the Stefan-Boltzmann law. The Stefan-Boltzmann law states that the total energy radiated from a blackbody is proportional to the fourth power of its absolute temperature. Our sun is by no means radiates energy like a blackbody but its spectral radiation is very close for this approximation. Here is what the sun’s radiations spectrum compares to a perfect blackbody (defined as Planck’s Law).
The Stefan-Boltzmann Law, in its analytical form appears as follows
Using the above equation we can calculate the average power (P) per area (A) the Sun produces on its surface. To calculate the temperature of a planet, which is a calculation of the power per area that the planet receives from the sun, we must scale our calculation for the surface of the sun by the surface area at which radiation moves out into space. This area is the surface area of a sphere 4*pi*D where D is the distance between the sun and the planet of interest. Putting this altogether produces an equation for the temperature of a planet, if the planet was heated solely by the sun and assuming that no radiation is reflected back (meaning zero albedo)
Temperature of a planet = (Ts^4*Rs^2/4*Dsp^2)^(1/4) : where Ts = temperature of the sun, Rs = radius of the sun, and Dsp = distance from sun to planet.
For interest sake let us calculate what the predicted temperatures of Venus, Earth, and Mars.
Ts ~ 5800 K, Rs ~ 695,500,000 meters, Dsvenus ~ 0.72*Dsearth, Dsearth ~ 149,597,871,000 meters, Dsmars ~ 1.52*Dsearth
Temperature of Venus = 56.5 degrees Celsius
Temperature of Earth = 6.6 degrees Celsius
Temperature of Mars = -46 degrees Celsius
For interest sake let us look at what the real average temperatures of these planets.
Real Temperature of Venus = 457 degrees Celsius
Real Temperature of Earth = 14 degrees Celsius
Real Temperature of Mars = -55 degrees Celsius
Relative to the real temperatures of the planets we find that our predictive temperatures are off by
+400.4 degrees for Venus which is a difference of 88%
+7.4 degrees for Earth : difference of 53%
-9 degrees for Mars (meaning it is colder then predicted) : difference of 16%
How can we be such a difference between our predictive methods and what is reality?
One possible reason is that I didn’t take into account any albedo effect. The albedo effect I didn’t include any albedo effects….the amount that the planet re-radiates back into space due to clouds or ground. Including this effect would in essence fix our predictive temperature of Mars since the real temperature of Mars is less then our predictive temperature. However including these effects for our predictive temperatures for Earth and Venus would decrease our predictive temperatures of our planets and not increase them, like we need. So what is the cause for the discrepancy for Venus and Earth. The only effect that could contribute to this increase in temperature, relative to our predictive theory, is that I didn’t take into account any greenhouse effect.
The greenhouse effect is defined as
1. An atmospheric heating phenomenon, caused by short-wave solar radiation being readily transmitted inward through the earth’s atmosphere but longer-wavelength heat radiation less readily transmitted outward, owing to its absorption by atmospheric carbon dioxide, water vapor, methane, and other gases; thus, the rising level of carbon dioxide is viewed with concern.
2. The phenomenon whereby the earth’s atmosphere traps solar radiation, caused by the presence in the atmosphere of gases such as carbon dioxide, water vapor, and methane that allow incoming sunlight to pass through but absorb heat radiated back from the earth’s surface.
3. A similar retention of solar radiation, as by another planet or in a solar panel.
4. Warming that results when solar radiation is trapped by the atmosphere; caused by atmospheric gases that allow sunshine to pass through but absorb heat that is radiated back from the warmed surface of the earth.
We must ask the question “What is the basic physics behind the greenhouse effect” before we truly understand what the greenhouse effect really is. For starters here are two quick movies that describe the greenhouse effect. Global Warming Movie One and Global Warming Movie Two : “For Kids”. Both of these little movies I highly recommend watching. They take two minutes each to view. ***Note*** Both of these quick movies also mention Global Warming. My intensions are not to convince the reader of Global Warming. These movies are used here for the sole purpose of trying to explain the concept of the greenhouse effect. Debating the issue of Global Warming will come later. Please try and not to mix these two different concepts.
The Earth receives electromagnetic radiation (light) from the sun and radiation leaves the Earth in two forms: reflected solar radiation (via the albedo effect) and emitted thermal infrared radiation. The Earth reflects about 30% of the incident solar flux; the remaining 70% is absorbed, warms the land, atmosphere and oceans, and powers life on this planet. Eventually this energy is re-radiated back into space as infrared photons. This thermal infrared radiation increases with increasing temperature (via Stefan-Boltzmann Law). One can think of the Earth’s temperature as being determined by the requirement that it produce the infrared flux needed to balance the absorbed solar flux.
The key to the greenhouse effect is the fact that the atmosphere is relatively transparent to visible solar radiation but strongly absorbing at the wavelengths of the thermal infrared radiation emitted by the surface and the atmosphere (See figures below). The visible solar radiation heats the surface, not the atmosphere. Whereas most of the infrared radiation escaping to space is being emitted from the upper atmosphere, not the surface. The infrared photons emitted by the surface are mostly absorbed by the atmosphere and do not escape directly to space.
The molecules/atoms that constitute the bulk of the atmosphere; oxygen (O2), nitrogen (N2) and argon; do not interact with infrared radiation significantly. While the oxygen and nitrogen molecules can vibrate, because of their symmetry these vibrations do not create any transient charge separation that enhances the interaction with radiation. In the Earth’s atmosphere, the dominant infrared absorbing gases are water vapor, carbon dioxide, and ozone, these molecules being “floppier” so that their rotation/vibration modes are more easily excited. For example, carbon dioxide is a linear molecule, but it has an important vibrational mode in which the molecule bends with the carbon in the middle moving one way and the oxygens on the ends moving the other way, creating some charge separation, a dipole moment. A substantial part of the greenhouse effect due to carbon dioxide exists because this vibration is easily excited by infrared radiation. Water has multiple effects of infrared radiation, through its vapor phase and through its condensed phases. Other absorbers of significance include methane, nitrous oxide and the chlorofluorocarbons. ***Note*** The last three paragraphs have been obtain by link
The atmosphere now is emitting infrared radiation both upwards and downwards which is caused by the greenhouse effect due to greenhouse gases. The upward infrared flux emitted by the surface must balance not only the absorbed solar flux but also this downward infrared flux emitted by the atmosphere. The surface temperature must rise until the surface generates enough thermal radiation to balance the sum of these two incident radiation streams.
The basic result is that Venus and Earth are WARMER, relative what they would be if they were solely heated by the energy of the sun, because of the greenhouse effect. The cause for our discrepancy for the temperature of Mars is because it has little to no atmosphere and hence the abledo effect plays an important role in the cooling of Mars which has an atmosphere that extends 1 to several meters from the ground.
Now that we have understood the ideas behind the greenhouse effect and greenhouse gases we may now ask the question: what happens if more greenhouse gases are released into our atmosphere as a result of human industrization or otherwise? This is the 64,000 dollar question. Everything use discussed in this blog is understood; all questions have been asked and answered. It is this question that was just proposed to the reader that leads us to the topic of Global Warming.
Let us first define what Global Warming is
1. An increase in the earth’s average atmospheric temperature that causes corresponding changes in climate and that may result from the greenhouse effect.
2. An increase in the average temperature of the earth’s atmosphere, especially a sustained increase sufficient to cause climatic change.
Before I attempt to answer the above question in a forthcoming blog, I will lead it up to the reader to comment and to make predictions. What will be the effect of adding additional greenhouse gases into the Earth’s atmosphere? Will it be minimal and nothing will happen? Will temperature of the Earth increase by a couple of degrees and if so what will be the effects of the slight temperature increase of the planet? Or will all hell break loose? You decide.