It is a tenet of catastrophic anthropogenic global warming theory (CAGW) that our carbon dioxide emissions are the major cause of recent global warming. Although carbon dioxide is a very weak greenhouse gas, CAGW theory holds that it is enough to start the warming process which, in turn, evaporates water, and water vapor is a very strong greenhouse gas. CAGW proponents ignore the fact that more water vapor in the air produces clouds which block the sun (more on that below).

It follows from CAGW doctrine that more carbon dioxide emissions should increase the humidity of the air, thus establishing an enhanced greenhouse effect. Is that happening?

A new paper, Trends in U.S. surface humidity, 1930 – 2010, Journal of Applied Meteorology and Climatology, finds just the opposite: “Average long-term trends (1930 – 2010) indicate that temperature has warmed, but little change has occurred in dewpoint and specific humidity.” In other words, the mechanism for CAGW’s enhanced greenhouse effect is not happening according to observational data.

How, then, do we account for warming in the 20^th Century? Back in 2005, Dr. Roy Spencer published a book: “The Great Global Warming Blunder: How Mother Nature Fooled the World’s Top Climate Scientists” (see my review here). In that book Spencer proposed that “The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling.” Could such a small change in cloud cover be significant?

A new paper just published in the Journal of Climate finds that global cloudiness has decreased over the past 39 years from between 0.9 to 2.8% by continent. See graphs and a discussion of the paper at WUWT here.

The first paper falsifies the major CAGW tenet; carbon dioxide has been increasing but there has been no increase in humidity. The second paper provides confirmation of a natural control of global temperatures.

For a more detailed discussion of climate sensitivity to carbon dioxide see here. “Examination of Earth’s climate sensitivity by varied derivation reveals climate to be remarkably insensitive to changes in forcing from enhanced greenhouse effect.” “Evaluation of Earth’s natural greenhouse effect reveals forcing response to be considerably less than line by line spectral radiance evaluation would suggest. Net feedbacks are found to be negative.”

See also:

A Perspective on Climate Change a tutorial

Carbon Dioxide and the Greenhouse Effect

Humans and the Carbon Cycle

CERN experiment confirms cosmic ray effect on climate

20^th Century temperatures explained as natural recovery from Little Ice Age

The “greenhouse effect,” very simplified, is this: solar radiation penetrates the atmosphere and warms the surface of the earth. The earth’s surface radiates thermal energy (infrared radiation) back into space. Some of this radiation is absorbed and re-radiated back to the surface and into space by clouds, water vapor, methane, carbon dioxide, and other gases. Water vapor is the principle greenhouse gas; the others are minor players. Without the greenhouse effect the planet would be an iceball, about 34 C colder than it is. The term “greenhouse effect” with respect to the atmosphere is an unfortunate usage because it is misleading. The interior of a real greenhouse (or your automobile parked with windows closed and left in the sun) heats up because there is a physical barrier to convective heat loss. There is no such physical barrier in the atmosphere.

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.

A soon to be published research paper from the University of Arizona states that rising sea levels will flood our southeast coast. The press release is titled: “Rising seas will affect major US coastal cities by 2100.” The research was conducted by Jeremy Weiss, a doctoral candidate in geosciences, Jonathan Overpeck, professor of geosciences and of atmospheric sciences and co-director of UA’s Institute of the Environment, and Ben Strauss of Climate Central in Princeton, N.J.

The press release says that greenhouse gas emissions will cause warming which will raise sea level by at least one meter by the year 2100. It also says that “warming will likely lock us into at least 4 to 6 meters of sea-level rise in subsequent centuries…”

In my opinion, this study is nothing more than speculative science fiction with little factual basis and it presents just another scary scenario that begs for government grant money.

I emailed Mr. Weiss asking for information on their sea level projections and asked this question: “What specific physical evidence do you have that carbon dioxide has a significant effect on global temperature?” He emailed some references to me (see below).

  On Sea Level

For sea level to rise one meter by 2,100 would require the current rate of sea level rise to more than triple beginning this year and continue for 89 years. For a review on measurements of sea level, see my blog: Sea Level Rising. Research documented in that article shows that sea level, as measured by world-wide tidal gauges, was rising 2.03 ± 0.35 mm/yr from 1904-1953 and 1.45 ± 0.34 mm/yr from 1954-2003. Satellite measurements indicate a rate of 3.2 mm/yr since 1994 with a decreasing rate since 2006. The apparent discrepancy between tidal gauges and satellite measurement is due to the fact that sea level rise is cyclic and the satellites started measuring at the bottom of a rising cycle. However, even using the higher number, it would require tripling of the currant rate of rise to produce a one meter sea level change by 2100.

In the press release, Weiss claimed to use “the most recent sea-level-rise science…” He referred me to two papers:

Pfeffer WT, Harper JT, O’Neel S (2008) Kinematic constraints on glacier contributions to 21st-century sea-level rise. Science 321:1340-1343.

The Pfeffer research was a computer modeling study but with no actual measurements. The abstract reads in part, “We find that a total sea-level rise of about 2 meters by 2100 could occur under physically possible glaciological conditions but only if all variables are quickly accelerated to extremely high limits. More plausible but still accelerated conditions lead to total sea-level rise by 2100 of about 0.8 meter.”

The other paper was: Vermeer M, and Rahmstorf S., 2009, Global sea level linked to global temperature. P Natl Acad Sci USA 106:21527-21532. This too is essentially computer modeling. I found two critiques of the Vermeer-Rahmstorf paper, one in the Proceedings of the National Academy of Sciences says their math was wrong; the other by a Senior Scientist at the US Department of Energy’s National Renewable Energy Laboratory lists multiple problems, including using out of date data and bad math.

Greenhouse gases and global warming

The “greenhouse effect” is this: solar radiation penetrates the atmosphere and warms the surface of the earth. The earth’s surface radiates thermal energy (infrared radiation) back into space. Some of this radiation is absorbed and re-radiated by clouds, water vapor, methane, carbon dioxide, and other gases. Water vapor is the principle greenhouse gas; the others are minor players. Without the greenhouse effect the planet would be an iceball, about 34 C colder than it is.

Since the press release said that greenhouse gas emissions (i.e., carbon dioxide) were responsible for the warming that would raise sea levels, I asked Mr. Weiss, “What specific physical evidence do you have that carbon dioxide has a significant effect on global temperature?”

At first, he emailed reference to two old textbooks and referred specifically to a chapter in one of them. I found that book online via Google Books. That chapter discusses the theoretical basis for climate modeling but presents no physical evidence to support the theory.

I asked again for sources and Mr. Weiss emailed links to abstracts of several papers in the scientific literature. It often requires a paid subscription to find the full paper online, but I did find some of them. Here are my comments on the papers Mr. Weiss referred to.

1. Harries, J.E., Brindley, H.E., Sagoo, P.J. and Bantges, R.J. 2001. Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997. Nature 410: 355-357.

2. Jennifer A. Griggs and John E. Harries, “Comparison of spectrally resolved outgoing longwave data between 1970 and present”, Proc. SPIE 5543, 164 (2004); doi:10.1117/12.556803

These two papers use satellite data to compare the strength of the greenhouse effect at two different times. A review from CO2Science.org says:

Harries et al. (2001) analyzed the difference between the spectra of outgoing longwave radiation obtained by two orbiting spacecraft that looked down upon the earth at periods of time separated by a span of 27 years. The data utilized were obtained over a specific area in the central Pacific (10°N-10°S, 130°W-180°W) and a “near-global” area of the planet (60°N-60°S). The data were further constrained by masking out land/island areas and areas believed to contain clouds.

The results of their analysis showed a number of differences in the land-masked and cloud-cleared data, which the authors attributed to changes in atmospheric concentrations of CH4, CO2, O3, CFC-11 and CFC-12 that occurred over the 27-year period separating the times of their two sets of measurements. Hence, they concluded their results provided “direct experimental evidence for a significant increase in the earth’s greenhouse effect” over the 27-year time interval. Such a conclusion, however, is somewhat misleading, for it does not provide direct experimental evidence for a significant increase in earth’s total greenhouse effect. It does so only for the cloud-free part of the atmosphere located over a portion of the planet’s oceans. Furthermore, research that has been conducted on the cloudy portion of the atmosphere over the oceans has revealed the presence of a highly negative feedback phenomenon that is capable of totally overpowering any temperature increase forced by the rise in greenhouse gases.

Furthermore, the attribution of cause is without supporting evidence. This is interpretation bias. Another review explains interpretation bias and cites other studies which show why the Harries conclusion is unjustified.

 3. Wang, K., and S. Liang (2009), Global atmospheric downward longwave radiation over land surface under all-sky conditions from 1973 to 2008, J. Geophys. Res., 114, D19101, doi:10.1029/2009JD011800.

These researchers estimated the downward longwave radiation over land for the period 1973 to 2008. The concluding sentence from their abstract: “The rising trend results from increases in air temperature, atmospheric water vapor, and CO2 concentration.” What did they expect? When the surface warms from any cause, we should expect these results. The results still provide no evidence on the significance of carbon dioxide emissions.

4. Evans, W.F.J. and Puckrin, E., 2009, Measurements of the Radiative Surface Forcing of Climate, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, D17107, 14 PP., 2009 doi:10.1029/2009JD012105.

The introduction says that these researchers used infrared spectrometers to measure the individual radiative flux of “a number of greenhouse gases”: CFCs, methane, nitrous oxide, carbon monoxide, carbon tetrachloride, nitrous oxide, and tropospheric ozone. Carbon dioxide is not mentioned, but they do show carbon dioxide in some tables. To obtain the greenhouse flux of individual gases, they used a simulation of the atmosphere. The researchers say that the total greenhouse radiation (excluding water vapor) has increased by 3.5 watts per square meter since pre-industrial times. They also say that the radiation from water vapor has doubled to over 200 watts per square meter. These data suggest that other than water vapor, other greenhouse gases in totality are minor players.

Dr. Roy Spencer, a NASA scientist, explains in a blog why measurements such as those obtained by Evans do not really show what they are claimed to show.

5. Murphy, D.M., et al., 2009, An observationally based energy balance for the Earth since 1950, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, D17107, 14 PP., 2009, doi:10.1029/2009JD012105.

This paper deals with the authors’ estimate of earth’s energy balance and the assumed forcings and feedbacks of atmospheric components. The Spencer comments above and in this article apply. This paper provides no physical evidence that carbon dioxide has a significant effect on temperatures.

The bottom line here is that Mr. Weiss could not provide unequivocal evidence to support the thesis. A point not addressed by any of the papers which mentioned some effect of carbon dioxide is that human emissions of carbon dioxide make up less than 5% of the total amount in the atmosphere. This makes the claim that human emissions are causing warming even more spurious. Much of science is speculation which investigates the what-ifs, but so is science fiction.