Carbon dioxide is a “greenhouse” gas, so let’s examine its theoretical and actual effect on temperature.

Even the IPCC agrees that the hypothetical capacity of carbon dioxide to change temperature is given by the formula: T_c = áln(C₂/C₁), where T_c is the change in temperature in degrees Centigrade and the term ln(C₂/C₁) is the natural logarithm of the CO₂ concentration at time two divided by the concentration at time one. The constant á (alpha) is sometimes called the sensitivity and its value is subject to debate. This relationship was proposed by Svante August Arrhenius, a physicist and chemist, around 1896. This logarithmic formula produces a graph in the form shown at the left. This shows that as the concentration of carbon dioxide increases, its effects have less and less influence. This graph is the pure theoretical capacity of carbon dioxide to warm the atmosphere in absence of any confounding feedbacks. The different curves represent different values of alpha.

  The reason it works this way is because carbon dioxide can absorb only a few specific wavelengths of thermal radiation. The current concentration of carbon dioxide has absorbed almost all available radiation in those wavelengths so there is little left for additional carbon dioxide to absorb. Notice too, that water vapor absorbs many of the same wavelengths of thermal radiation. Also notice that in a certain part of the spectrum there is an open window of no absorption.

We see, therefore, that increasing levels of carbon dioxide in the atmosphere will have a decreasing hypothetical effect on temperature. That is also why our proposed attempts to decrease atmospheric carbon dioxide will have almost no effect on temperature.

The IPCC says that warming will produce more water vapor which will enhance greenhouse warming, a positive feedback. All their climate models are based on this assumption. Sounds reasonable except in the real world, it doesn’t happen. Increased water vapor produces more clouds which block the sun thereby inducing cooling, a negative feedback.

Dr. Roy Spencer explains here why doubling the carbon dioxide concentration in the atmosphere will add only 3% to Earth’s greenhouse effect. Spencer has further discussion here in which he says, “that about 50% of the surface warming influence of greenhouse gases has been short-circuited by the cooling effects of weather.”

The atmosphere is not static; we have weather which tends to dissipate heat into space. According to real world measurements, the negative feedbacks overwhelm the theoretical positive feedback posed by the IPCC.

An example of negative feedbacks:

In 2001, a paper by M.I.T. researchers proposed that warming dissipated high-altitude cirrus clouds which had the effect of dumping heat into space, thereby helping to regulate earth’s temperature. This paper was controversial because it went against the orthodoxy of global warming and there were many detractors. However, in 2007 researchers from the University of Alabama, using NASA satellite data found evidence to support the theory. In 2009, the original M.I.T. researchers, using National Centers for Environmental Prediction’s 16-year (1985-1999) monthly record of sea surface temperature, together with corresponding radiation data from the Earth Radiation Budget Experiment, found more real world evidence in support of the theory (see PDF). It might be noted that 11 major climate models used by the IPCC assume positive feedback, but real world data shows a temperature-moderating negative feedback. However, the role of clouds is still poorly-understood and more real-world data is needed.

What happens on other planets:

Venus:

Venus has a surface temperature of about 900 F and an atmosphere composed of 96% carbon dioxide. The temperature is the same from equator to poles, from day to night (Venus rotates on its axis in 2,802 hours rather than 24 hours). Venus is often touted as the extreme example of run-away greenhouse warming. But, there is almost no greenhouse warming on Venus because little, if any, direct sunlight gets to the surface. The atmosphere is too thick. In 1975, the Russian Venus lander Venera 9 measured clouds that were 30–40 km thick with bases at 30–35 km altitude. The surface air pressure on Venus is about 92 times greater than that on Earth. The high pressure alone can explain most of the high surface temperature. Although Venus gets almost twice the solar irradiation of Earth, Venus’ high albedo reflects back 65% of the sunlight.

 Venus has almost no water vapor in the atmosphere (about 0.002%), and therefore lacks the major greenhouse gas that Earth has.

Mars:

Mars has an atmosphere composed of 95% carbon dioxide and only a trace of water. Its atmosphere is very thin. Its surface pressure is about 2% that of Earth. The temperatures on the two Viking landers, measured at 1.5 meters above the surface, range from + 1° F, ( -17.2° C) to -178° F (-107° C). However, the temperature of the surface at the winter polar caps drop to -225° F, (-143° C) while the warmest soil occasionally reaches +81° F (27° C) as estimated from Viking Orbiter Infrared Thermal Mapper (NASA data). Again, no water vapor, no greenhouse effect.

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The greenhouse model is a simplified story that helps explain how our atmosphere works. However, the real world is very complicated and still not fully understood. Even global warming alarmist James Hansen of NASA’s Goddard Institute for Space Studies, had this to say: “The forcings that drive long-term climate change are not known with an accuracy sufficient to define future climate change.” — James Hansen, “Climate forcings in the Industrial era”, PNAS, Vol. 95, Issue 22, 12753-12758, October 27, 1998.

And even the IPCC once admitted, “In climate research and modeling, we should recognize that we are dealing with a coupled non-linear chaotic system, and therefore that the prediction of a specific future climate state is not possible.” — Final chapter, Draft TAR 2000 (Third Assessment Report), IPCC.

Human carbon dioxide emissions are 3% to 5% of total carbon dioxide emissions into the atmosphere, and about 98% of all carbon dioxide emissions are reabsorbed through the carbon cycle. (Source )

Although Earth’s atmosphere does have a “greenhouse effect” and carbon dioxide does have a limited hypothetical capacity to warm the atmosphere, there is no physical evidence showing that human carbon dioxide emissions actually produce any significant warming. If you disagree with that statement, then produce some physical evidence to refute it.

UPDATE March 3, 2011: A new paper in Geophysical Research Abstracts (Vol. 13, EGU2011-4505-1, 2011) reports that detailed spectrographic analysis found that because of the overlap absorbance of the much more abundant water vapor for long wave radiation, the effective sensitivity of carbon dioxide and methane as greenhouse gases is only one-seven that claimed by the IPCC and used in climate models.

Meteorologist Dr. Roy Spencer is a principal research scientist at the University of Alabama in Huntsville, formerly a senior scientist for climate studies at NASA, and now leads the U.S. science team for the Advanced Microwave Scanning Radiometer for EOS on NASA’s Aqua satellite. Dr. Spencer is the co-developer of the original satellite method for precise monitoring of global temperature from Earth orbiting satellites.

Dr. Spencer makes two main contentions in his book. First, the climate is much less sensitive to carbon dioxide than the Intergovernmental Panel on Climate Change (IPCC) says it is. This means that carbon dioxide is not a significant driver of temperature. Second, the Pacific Decadal Oscillation (PDO) alone can account for most of the temperature variation in the 20^th Century and can account for 75% of the global warming. He supports these contentions with both observational and experimental evidence in the book. Spencer published this evidence in the peer-reviewed, Journal of Climate in 2008, but it was ignored by the IPCC and by the mainstream press – hence the book. He is taking his case to the public. The book is written in layman’s terms with easy-to-understand examples of how the climate works. He also takes on the establishment and shows how there is a vested interest in maintaining the fiction that there is a climate change problem.

Some excerpts:

“Conceptually, there are two main processes that govern any kind of climate change: forcing and feedback.” This is cause and effect, which Spencer says the IPCC has gotten mixed up.

“Worries over catastrophic global warming rest entirely on the belief that our climate system is very sensitive, that is, dominated by positive feedbacks, which amplify any warming or cooling influence. A few scientists are predicting planetary doom as a result of our burning of fossil fuels, and politicians are now using standard propaganda techniques to convince you that we must act quickly to save the Earth.”

“Whether it is the Earth’s climate, or a pot of water on the stove, a temperature change is always caused by an imbalance between energy gained and energy lost.”

“While forcing (an energy imbalance) determines whether a temperature change will occur, feedback determines how big that temperature change will be. It is feedback that ultimately determines whether man-made global warming is catastrophic, or merely lost in the noise of natural climate change.”

“A mix-up between cause and effect in observations of cloud behavior from satellites has led to the false illusion that our climate system is dominated by positive feedback. This, in turn, has led to the development of highly sensitive climate models that predict large amounts of global warming. But when the separate influences of forcing and feedback (cause and effect) are isolated, recent satellite data reveal the climate system to be dominated by negative, not positive, feedback.”

“In order to convince Congress to fund research into a problem, you must first convince them that a problem exists. This automatically makes man-made global warming a particularly lucrative field for funding – as long as the threat of man-made global warming continues. There are managers at NASA, the National Oceanic and Atmospheric Administration, the National Science Foundation, and the Department of Energy whose careers now depend on a continuous flow of research dollars through them to the science community.” Spencer notes that his own research funding comes from NASA.

“…natural cloud fluctuations in the climate system will cause a bias in the diagnosed feedback in the direction of positive feedback, thus giving the illusion of an overly sensitive climate system.”

(This statement follows a discussion of radiative and non-radiative forcings; read the book to find out what these are.)

” … the IPCC has ignored… radiative forcing generated internal to the climate system as a potential source of climate change.” What that means is “that the climate models are too sensitive, which is why they predict so much global warming for the future. In contrast, the satellite evidence indicates that the climate system is quite insensitive, which means that it doesn’t really care how big your carbon footprint is. Rather than 1.5 to 6 deg. C (or more) of warming as predicted by the IPCC, a careful examination of the satellite data suggests that man-made warming due to a doubling of atmospheric carbon dioxide could be less than 1 deg. C (1.8 deg. F) – possibly much less.”

“It would take natural variations of little more than 1 percent in global average cloud cover to explain most of the climate change seen in the last 2,000 years, yet our ability to measure such small changes has existed for only the last ten years.”

“The idea that nature was in delicate balance before mankind came along is religious, not scientific. Given the necessity of carbon dioxide for life on earth, we need to consider the possibility that more CO₂ in the atmosphere will be better for life on earth, not worse.”

I recommend this book. It is a good read. It gives an easily understandable explanation of how the climate works. The book is available from Amazon.com.