In the previous posting, College Students Lack Scientific Literacy?, we took a quick look at the role of photosynthesis in the Carbon Cycle. This posting will examine the part that burning of fossil fuels play in the carbon cycle and how fossil fuel CO2 affects global warming.
There are those who believe that catastrophic heating of the Earth will result if fossil fuels use is not curbed or perhaps stopped all together. They think that the extra increment of CO2 from fossil will cause the climate to reach a “tipping point” after which there may be no turning back.
So what is the argument about between skeptics and believers?
Broadly speaking the believers have looked for a cause of a temperature increase of something less than 1C during the last century. They say that the measured volume of Carbon Dioxide (CO2) in the atmosphere has gone up coincident with the temperature increase and that since CO2 is a known greenhouse gas, it must be the cause. And they add that CO2 from industrial and transportation sources, a product of fossil fuel combustion, is the reason for the atmospheric CO2 increase from the past “steady-state” measurements.
Skeptics, while accepting that the Earth’s temperature has increased in the last century, so has it for the last 10,000 years since the end of the last Ice Age. And further, this cold to warm and return to cold has been going on for hundred thousands of years, so the last century’s warming is probably due mostly to natural causes. Skeptics say that the past history of temperature increases and CO2 variation as charted from the examination of ancient ice cores show the temperature change leads CO2 change both increasing and decreasing. Stated in another way, CO2 follows a change in temperature rather than leading the change. By the way, Al Gore’s “An Inconvenient Truth” movie did show it the other way but it is widely agreed that was wrong as was so much else of that science fiction documentary.
The amount of CO2 in the atmosphere is very small, and the CO2 increment from fossil fuel burning is about 3% of the total atmospheric CO2 content. If pressed the believers will agree that the primary greenhouse gas is not CO2, but rather water in the form of vapor and clouds. From 90 to 95% of the greenhouse gas effect results from water in the atmosphere.
An interesting way to look at the CO2 versus water has been made by Art Horn in his posting “The Utter Futility of Reducing Carbon Emissions”which can be seen by clicking here. This posting looks at the Carbon Cycle and it uses the Intergovernmental Panel on Climate Change, as the data source. This panel is the believer’s bible. Quoting from his posting:
“…….the Intergovernmental Panel on Climate Change (IPCC) 4th Assessment showed that 3% of the atmospheric CO2 comes from man-made sources. Global gross primary production and respiration, land use changes, plus CO2 from the oceans totals 213 gigatonnes of carbon exchanged each year between the Earth/oceans and the atmosphere. The IPCC figure also shows man-made carbon emissions to be about 7 gigatonnes, bringing the total to 220 gigatonnes per year. So from this, we can see that making energy from fossil fuels is producing about 3% of the carbon dioxide added to the air each year. From that, the total human component of the greenhouse effect is therefore about 3% of the total carbon dioxide component of the greenhouse effect, which is 8%.
That gives us a value of .2% from man-made carbon dioxide. If you think that’s a small number you’re right.”
A little more simple science is necessary to get this picture.
Greenhouse Gas (GHG) effect
To begin with, the simplest view is that GHG is a study of “energy in = energy out”. The “energy in” is the radiation from the Sun—sunlight, infrared (IR) and ultraviolet (UV)—that is absorbed by the Earth. The Earth then radiates this energy back out into space. On its way back out into space, some of it is delayed by interaction with trace elements in the atmosphere. This interaction increases the temperature of the atmosphere, and the Earth’s temperature rises. The greenhouse effect is real and it allows life, as we know it, to exist. If the Earth had no atmosphere, its temperature would be 255K (-18C). The average temperature of the entire Earth averaged over seasons is, by measurement, about 288K (15C). Thus the greenhouse effect results in an increase in temperature of about 33K (33C).
Lets look at GHG in more detail. The Sun energy in the form of visable light, IR, and UV (shortwaves) pass through the Earth’s atmosphere and are absorbed by the ocean, the land, the trees, concrete, road surfaces, etc. Not all of the Suns energy makes it to the Earth’s surface due to clouds and surface reflection, along with atmospheric scatter that represent a blockage. When the Sun’s input ceases, at night for example, these Earth objects begin to emit electromagnetic radiation. This radiation is in the infrared range but because the temperatures of the objects are much lower than that of the Sun, the wave lengths are different. They are much longer. For our purposes the Earth’s radiation will be called the longwaves.
The interaction of the trace compounds in our atmosphere with the outgoing longwave radiation is dictated by atomic absorption. Each compound in the atmosphere has a specific wave length band(s) that it absorbs. If the compound’s wave lengths correspond to the wave lengths of some of the IR radiated from the Earth’s surface, the IR waves can be absorbed. Those IR waves are converted to heat causing the compound to emit IR of a different wave length. The compound is transparent to other IR wave lengths.
Water, CO2 and Methane will absorb IR wave lengths emitted from the Earth. Of the emitted IR waves that are absorbed, it is estimated that some 4%to 6% are by CO2. The CO2 greenhouse effect is limited because the wave lengths that CO2 absorbs only represent a small part of the wave length ranges of the reemitted IR from the Earth. In fact, adding more CO2 to the atmosphere has only limited significance because the amount of CO2 already in the atmosphere is nearly sufficient to absorb those particular Earth originated IR waves.
Well, why do the believers think that CO2 will cause the very high Earth temperatures they trot out frequently to scare all the rest of us. They agree that water is the primary greenhouse gas. They think that the little upward bumps in temperature that are possible if more CO2 is added to the atmosphere will result in more water vapor in the atmosphere. They know that CO2 can’t do the deed so they have programmed their computers models (GCM) to gee-up lots of water vapor to do the deed. This amplification of the total greenhouse gases (GHG) is called positive feedback. Using this positive feedback, the GCMs forecast climate out some 100 years or more and conclude that global temperatures will rise dramatically. The problem is that this positive feedback is difficult to impossible to demonstrate in the real world. (Basically the world abhors positive feed back.) Meanwhile a negative feedback has been shown to exist in real world, making run-away global temperatures quiet unlikely.
Very little of the CO2 in the atmosphere is due to the burning of fossil fuels.
The GHG effect is primarily due to water as vapor or clouds
CO2 can only absorb a limited portion of the Earth’s radiated IR
The Believers proclamations of catastrophic weather conditions are based computer programs. Those computer predictions that were done sufficiently long ago to be meaningful as a predictions, have been notorious failures.
And the concept of Positive Feedback increasing water in the atmosphere resulting in large increases in the Earth’s temperature is a fiction of the computer program as it has not yet been proved in real experimental work.