Arvid Pasto
August 2024
A key climate parameter, called “climate sensitivity,” has been the subject of scientific study for literally hundreds of years. This parameter essentially indicates the degree of global temperature increase caused by a doubling of atmospheric CO2 levels. If the value of the parameter is 2, then the world's temperature will rise by 2°C if atmospheric CO2 levels reach twice today's levels. It is therefore implicitly a constant number. Scientific estimates vary widely, from much less than 1 to well over 6 (see below). Knowing its exact value is “priceless” to climate modelers and alarmists, much like the Golden Fleece was to its owner(s) in Greek mythology.
Since global warming is believed to be due to the presence of greenhouse gases in our atmosphere, much attention has been paid to assessing the impacts of these gases (mainly CO2, methane and nitrous oxide, as well as a variety of other gases that typically occur at very low concentrations).
It is foolish to attribute global temperature change to a single factor such as CO2. Beer's Law1 describes the well-known phenomenon of “saturation” where as CO2 levels increase, the atmospheric temperature increases rapidly from a CO2 level of 0. However, the temperature increase is NOT linear. Instead, it decreases and eventually appears to stabilize. (Figure 1) So you can see that using only one factor, climate sensitivity is NOT a constant. However, at high CO2 levels, climate sensitivity can be considered “nearly” constant. There is a perfectly good reason for this behavior, as can easily be shown1. The main result of this statement is that after a certain amount of CO2 is released into the atmosphere, any additional amount of CO2 will result in smaller temperature increases. Above a certain level, these increases will be insignificant.
Figure 1. The influence of CO2 concentration on atmospheric warming
(From page 8 of The Skeptics Handbook, Joanne Nova 2009)
The same nonlinear relationship applies to all gaseous substances in the atmosphere. And of course our atmosphere consists of everything, but not just one gas. Each of these gases has its own self-flattening concentration-temperature curve depending on its properties.
In theory, it should be easy to calculate the resulting absorption curve if one knows the exact composition of the atmosphere and the required spectroscopic properties of each gas. The global temperature of the Earth is thought to be determined by a balance between the incoming solar radiation plus the heat generated by the Earth itself and the outgoing heat (radiation).
Gaseous molecules absorb heat from both incoming and outgoing radiation. The incoming heat is absorbed primarily through electronic transitions, while the outgoing heat is absorbed through vibrations and/or rotations of the molecules. These interactions can be easily measured spectroscopically, with each species exhibiting a different absorption spectrum versus radiation wavelength (or frequency). See Figure 2.
Figure 2. Energy absorption by various gases as a function of the wavelength of the incident radiation and its effect on the incoming solar and outgoing terrestrial radiation. (From a presentation by Dr. William Happer of Princeton University at Marshall University)
One can then calculate how much heat is generated in the atmosphere by these processes, since the specific heat of each constituent is known. The calculation essentially asks: how much heat is generated and how much temperature change does this heat then cause?
Such calculations have been performed for many years and produce results like those shown below. These calculations allow a more accurate estimate of the “greenhouse gas effect” of a given gas, since one can simply double the concentration of the species of interest in the calculation and see what happens. (Figure 3)
Figure 3. This figure shows that increasing CO2 levels from 0 ppm (green line) to 400 ppm (approximately today's level, black line) has a significant impact, raising the Earth's temperature from the zero CO2 level (about -8 °C) to today's level (about 16 °C). It can be clearly seen that doubling CO2 levels to 800 ppm has almost no impact (red line). [Ron Clutz.com 2021]
The two main evils of climate change, CO2 (carbon dioxide) and CH4 (methane), are easily demonstrated as unlikely causes of significant global warming using calculations such as those discussed above. Both are known to be increasing continuously (Figures 3 and 4) and have been presented as the main cause(s) of global warming for decades.
Figure 3. CO2 concentration in the Earth’s atmosphere until 20232.
Clearly, something is missing from these global warming calculations. Many factors that are not due to gases warming the atmosphere are easy to infer. These include assumptions about how much incoming solar radiation is reflected or absorbed by clouds or the oceans, how much incoming light is scattered by clouds or “dust” in the atmosphere, how much incoming light is reflected by clouds or by ice and snow on Earth, and many others. The latest climate models have defined all of these terms in great detail (Figure 5).
Other factors that are difficult to explain include external heat sources (underwater volcanoes, underground coal or methane fires), soot deposited on glaciers (which absorbs heat), recent huge forest fires around the world (which generate heat, soot and CO2), and others.
Finally, there are the so-called “feedbacks”: these include interactions between two gases, such as CO2 and water vapor, and others. These can be positive, where the presence of one gas, such as CO2, is thought to increase the presence of another gas, such as water vapor, due to increased evaporation from the oceans. But they can also be neutral or negative. (Figure 6) The heat inputs, called “drivers,” are added to the “feedbacks” in climate models.
Figure 6. Climate feedback taken into account in global climate models. [From IPCC AR4 report.]
The water vapor feedback is particularly problematic: it is NOT known to be “positive,” and certainly not as positive as climate scientists claim.
Because there are so many influencing factors and complicated feedbacks, it is impossible to calculate climate sensitivity a priori. You always have to make assumptions. But that is exactly what scientists have been trying to do for decades in vain. (Figures 7, 8, 9)
Figure 7. Scientific estimates of climate sensitivity. In 2013, Nobel Prize-winning physicist Nur Shaviv said of this graph: “Seriously, let me compare this to the most boring graph I've ever made in my life. Below is the likely range of climate sensitivity as a function of time. As you can see, the likely range of climate sensitivity has not changed since the 1979 Charney report, except for AR4 with its slightly smaller range mentioned above. In other words, although we may have invested billions of dollars in climate research over more than three decades, our ability to answer the most important question of climate has not improved in the slightest!”
( https://www.climatedepot.com/2013/10/09/award-winning-israeli-astrophysicist-dr-nir-shaviv-the-ipcc-and-alike-are-captives-of-a-wrong-conception -der-IPCC-gibt-immer-nicht-sein-Bestes-um-den-Beweis-zu-vermeiden-dass-die-Sonne-eine-große-Wirkung-hat/ )
Figure 9. Historical estimates of climate sensitivity.
It turns out that the notion of climate sensitivity is actually physically useless, except to show what influence certain forcing factors or feedbacks can have on global warming. Global atmospheric temperature can now be measured directly 24 hours a day via satellites and/or weather balloons, ocean temperature via submersible buoys, and “earth” temperature via thermometers on every continent. (The latter two have their own problems, particularly surface measurements, but these are not discussed here.)
Global climate models currently running on supercomputers around the world do not use “climate sensitivity” as an input, but their output can be used by generalists to infer its value based on the computer’s input and output.
Comparing the results of actual global temperature with the results of computer climate models (black line in Figure 10), one can see that the Earth's temperature is NOT rising nearly as fast as a “climate sensitivity” of over 2 would predict.
Global CO2 was 2,332 ppm in 1976 and the initial temperature change was assumed to be 0.00. In 2016, CO2 was 404 and the temperature increase was 0.3°C. At an average rate of increase of 2 ppm/year, it would take 166 years for the level to double since 1976. {I use 2 ppm/year although it was 1.8 ppm/year from 1976 to 2016 but has recently increased to over 2 ppm/year}. Now 40 years represents 0.24 of this time difference (40/166). Thus the “climate sensitivity” from 1976 onwards would be 0.3°C/0.24 or 1.25. If the climate sensitivity (CS) had been 2, the expected temperature increase would have been 0.48°C, and if it had been 3, the increase would have been 0.72°C, and so on. The average of the climate models shown in the graph gives a value between 4 and 5 for climate sensitivity (and increasing).
Figure 10. Comparison between predictions of computer climate models and the actual observed global temperature. [From Dr. John Christy, Univ. Alabama-Huntsville]
If the rate of CO2 increase dramatically over the next few decades, climate sensitivity will also increase and with it the projected global temperature. In fact, the rate of CO2 emissions is expected to slow down, lengthening the CO2 doubling time and reducing climate sensitivity.
However, since current temperature and CO2 data lead to a climate sensitivity of about 1.25, there is clearly something wrong with the current “trend” of a climate sensitivity of 3 or more.
AND… the real problem with the term “climate sensitivity” is that it suggests that CO2 is the driver of climate change, which it is not.
REFERENCES
- MN Berberan-Santos, “Beer's Law Revisited,” Jour. Chem. Ed. 67, September 1990
- https://www.statista.com/statistics/1091926/atmospheric-concentration-of-co2-historic/q
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