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Myths believed by some AGW skeptics

Roy Spencer finally wrote a text that I wanted to write for quite some time:

In defense of the greenhouse effect
We frequently hear arguments from the fellow skeptics that the greenhouse effect has to be impossible, exactly zero, that it contradicts some basic laws of mechanics, thermodynamics, and so on.

Well, these thoughts lead to the correct practical conclusions: it is absurd to spend trillions to "fight climate change".

But from a scientific viewpoint, all these statements are as ludicrous as the statements of the alarmists that the ongoing "climate change" threatens life on the Earth. Every effect that cannot be proved to be zero - by symmetries and closely related principles - is guaranteed to be nonzero. That's why there are so many other effects, too. The only question are the coefficients, i.e. the strength of all these effects.

As Roy Spencer explains, the greenhouse effect is technically different from the effect used in the greenhouse with vegetables. The greenhouse effect is about the infrared absorption while the greenhouse mechanically prevents heat convection. But both of them reduce the ability of the system to cool down, which means that the equilibrium temperature increases. The only question is how much.

The bare value (neglecting rain, effects on other parts of the atmosphere etc.) can be calculated for the CO2 greenhouse effect from well-known laws of physics: it gives 1.2 °C per CO2 doubling from 280 ppm (year 1800) to 560 ppm (year 2109, see below). The feedbacks may amplify or reduce this value and they are influenced by lots of unknown complex atmospheric effects as well as by biases, prejudices, and black magic introduced by the researchers.




Chris Colose, an AGW advocate, attempted to criticize Richard Lindzen's demonstration that positive feedbacks cannot dominate. Well, the best thing he could do was to use some alternative graphs to argue that the current models underestimate the negative feedbacks by a factor of 2-3 rather than 5-7. This factor of 2-3 corresponds to no feedbacks. Well, a multiplicative discrepancy by a factor of 2-3 is still a pretty bad rating for the models, isn't it?

And let me tell you something else, too. So far, I can't reproduce some of Richard Lindzen's numbers. For example, Richard says that we have already realized 70% of the warming resulting from the CO2 doubling. I can imagine that a more complete calculation (involving overlapping spectral lines with other gases?) gives this result. But the simple logarithmic calculation I can do gives me a different result:
Log[385/280] / Log[560/280] = 0.46
In other words, we have made about 46% of the warming expected from doubling so far. It's almost 50%. So because it has led to something like 0.6 °C so far, assuming that we generously attribute the whole 20th century change of the global mean temperature to the CO2 enhanced greenhouse effect, we may expect that the rest of the doubling will lead to additional an 0.6 °C of warming: the total sensitivity is thus 1.2 °C per CO2 doubling, just like expected from the bare greenhouse effect. There are other, independent calculations leading to a similar value, including the calculation by Stephen Schwartz and pretty good reconstructions by Svensmark et al. who describe the 20th century temperature in terms of galactic cosmic rays, ENSO phenomena, volcanos, and a 1+ °C per century linear trend.

Note that the doubled value, 560 ppm, will be reached in 100 years from now (2109) because
560-385 ppm = 175 ppm = 1.75 ppm x 100
and the rate around 1.75 ppm of added CO2 per year seems to be pretty constant for quite some time. In the next 100 years (2009-2109), I expect 0.6 °C warming from the increased CO2 concentrations, assuming business-as-usual for 100 more years. This contribution will be lost in the noise of many other contributions of both signs. And it makes no sense to extrapolate the calculation beyond 2109 because people in 2109 will surely make their own decisions. Moreover, it is likely that their dependence on fossil fuels may already be reduced and new technologies to produce energy (or manipulate the climate) may be available.

Richard Lindzen says that the net climate sensitivity is only 1/2 of my "neutral" value (or less) and I don't quite understand his calculation. But let's admit that it would be extremely difficult to distinguish the two figures by measurements in the 21st century because those 0.3 °C of difference are hidden in the noise of dozens of other effects.

More importantly, I think that even my "neutral" answer, 0.6 °C of warming per century, clearly poses no threat to us or other life forms on Earth. After all, we have seen the very same warming in the 20th century (our CO2 output has increased, but the effect of each CO2 molecule has dropped, because of the logarithmic law) and there have been no detectable negative consequences of it for the Earth whatsoever. It is therefore extremely awkward to expect something dramatic to happen from the same small increment repeated once again.

I may expand this text later.

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reader Jacob said...

I think it would be fairly simple to devise an experiment to measure the greenhouse effect empirically.
Take a pipe, isolate it, fill it with a controlled atmosphere, containing various measured concentrations of CO2 and water vapor. Beam a long wave (infrared) beam trough it. Measure the intensity or energy of the beam at the other end of the pipe. Measure the temperature of the pipe and the air in it.
Sounds simple to me.

Has anyone done this? Could anyone point to a paper describing the results of such an experiment? If not - why not ?


reader Jacob said...

I think it would be fairly simple to devise an experiment to measure the greenhouse effect empirically.
Take a pipe, isolate it, fill it with a controlled atmosphere, containing various measured concentrations of CO2 and water vapor. Beam a long wave (infrared) beam trough it. Measure the intensity or energy of the beam at the other end of the pipe. Measure the temperature of the pipe and the air in it.
Sounds simple to me.

Has anyone done this? Could anyone point to a paper describing the results of such an experiment? If not - why not ?


reader Lumo said...

Dear Jacob, it is indeed easy to measure - and even theoretically calculate - the bare greenhouse effect. See e.g.

Why is the greenhouse effect logarithmic?

for very detailed formulae. The main result is that the doubling of CO2 leads to 1.2 °C of warming of the atmosphere, if there are no other effects. In the real world, there are however many effects, feedbacks, and it is not even known for sure whether these effects reduce or amplify the bare effect. This makes the whole controversy, at the scientific level. General principles and indirect observations suggest that the feedbacks are negative - i.e. reducing the bare value. The alarming predictions are derived from positive feedbacks that are not supported in any scientific way - only by unverified (and often demonstrably inaccurate) models that simply assume large positive feedbacks.


reader Bob Armstrong said...

I’d appreciate critiques of my implementation at http://cosy.com/Science/TemperatureOfGrayBalls.htm of the classical physics of radiantly heated balls like ours . The main point is that the rather ubiquitous explanation of the “need” for a “greenhouse effect” as repeated on Wikipedia is clearly wrong being based on the false notion that the albedo of a radiantly heated ball effects its equilibrium temperature . The correct 19th century physics is implemented in a few lines of an array programming language generating experimentally falsifiable numbers . I have never found an experimental demonstration of the purported greenhouse effect or even any quantitative explanation of it in terms of basic physics .

The extension of my implementation to colored spectra so that quantitative values can be computed for the couple of skinny lines of CO2 — or any other spectrum still needs to be done .