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Gary Novak argues (e.g. in his book, Science Errors and on his web site) that climate models are incorrect, because of a missing "dilution" factor.

Climatologists skipped over the dilution factor. Each CO2 molecule in the air would have to be 2,500°C to heat the air 1°C—an impossibility—because there are 2,500 air molecules around each CO2 molecule (400ppm). There cannot be greenhouse gases creating global warming for this reason.

Is this statement true?

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    The claim is quite a bit silly. It shows a severe lack of understanding of the well understood, well researched field it is referring to, basically turning this into a science question that needs to be answered with a couple of physics lessons. I don't think there is much to salvage here. I'd vote to close this as off-topic and redirect the OP to physics.SE or somesuch. – DevSolar Dec 9 '16 at 8:28
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    @James: I am sure you will find the atmosphere of Venus a fascinating subject. Greenhouse gasses and their effects are well-researched, and well understood. The valid questions regarding climate change and the human influence on it are about quantities, points of no return, and scope, not about the basic mechanics. Ref. Is CO₂ the cause for Global Warming? – DevSolar Dec 9 '16 at 8:31
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    @DevSolar "Shows a severe lack of understanding of the field" sums up most of the global warming denial arguments pretty well. – Shadur Dec 9 '16 at 9:25
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    A classical example of not even wrong. – gerrit Dec 9 '16 at 10:38
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    Wow, this guy has absolutely no understanding of the basics of physics and glorifies his own ignorance. – Sklivvz Dec 11 '16 at 20:20
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Each CO2 molecule in the air would have to be 2,500°C

This is wrong because molecules collide with each other, transferring their kinetic energy.

As explained in Elements of Physical Chemistry by Atkins et al.:

the collision frequency of a typical gas is about [1,000,000,000 times per second] at 1 atm and room temperature, so the time in flight in a gas is typically 1 ns [nanosecond]

So a given molecule (such as a CO2 molecule) can not have a higher kinetic energy than the other molecules in the gas for more than the nanosecond time scale. Instead, the energy is distributed among the molecules by collisions.

For more information see Properties of Gases.

Separately, the claim is wrong to compare the full 400 ppm of CO2 to only 1°C.

Instead, without a greenhouse effect, Earth's temperature would be -18 °C compare to the 1951 and 1980 temperature of 14 °C.

So the total greenhouse effect is about 32 °C, and CO2 is responsible for 9-26% of the effect. H2O is the main contributor, at 60%, according to the American Chemical Society, but humans do not control H2O concentration, except by otherwise changing temperature.

More particularly, the 32 °C of greenhouse effect, based upon the average 1951 and 1980 temperature of 14 °C, should be compared to the corresponding CO2 concentration of 320 ppm in 1965. Increase in temperature since then should be compared relative to increase in CO2 concentration since then, while considering any hysteresis effects (such as time for oceans and ice to equilibrate to new temperature).

Also, the claim is wrong to assess that only the air needs to be heated to the new temperature. The heat capacity of the ocean is much greater than the atmosphere.

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    The statement is definitely wrong, but it does actually make physical sense. If we assume the math checks out, then if magically the CO2 molecules gained energy until they were at 2500 C instantly, then those collisions would distribute that energy, and (again, assume the math was actually correct) that energy would equal a 1 C increase in average temperature for Earth. That logic is a Solid what if scenario. Of course, Global warming does not work like that at all, which is why its still wrong. – Ryan Dec 9 '16 at 21:44
  • @Ryan but it would need to be much more than the energy corresponding to 2500 C, because with zero CO2 the Earth would be much colder than the coldest ice age. The claim is additionally wrong for comparing the full 400 ppm to 1 degree C. – DavePhD Dec 9 '16 at 22:12
  • I dont think he actually compares 400 ppm to 1°C in any way, shape, or form. He is actually using the most basic of math ideas. 400 PPM means 2500 molecules of air per CO2 molecule (1M/400 = 2500). So, if one molecule of air (CO2) increases by 2500°C, that is kind of equivalent to 2500 molecules of air increasing by 1°C, from a basic logical standpoint. So there is no claim about the relationship between PPM and °C, nor an implication that 800 ppm would mean 2°C. It looks like your giving the claim too much credit here. – Ryan Dec 12 '16 at 17:22
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No, it's not true. Here's a 60-second explanation of global warming.

It's conservation of energy. Fourier asked in 1824: the earth receives a continuous stream of energy from the sun. Why doesn't it keep getting hotter and hotter?

The answer is that the earth also radiates heat into space. A warmer object radiates more heat, so the earth warms up to a temperature where the incoming solar energy and the outgoing thermal energy balance each other ("equilibrium temperature").

As long as the incoming energy and outgoing energy balance each other, the total amount of energy in the system (land, oceans, atmosphere) remains the same, and the climate remains stable.

Hasn't climate changed in the past? Yes: if the brightness of the sun changes, or if there's variations in the earth's orbit, or if the reflectiveness of the earth changes, or if volcanic activity changes the composition of the atmosphere, these can all affect the energy balance, and therefore make the equilibrium temperature higher or lower.

But we can measure all these things, and right now only one of them is changing dramatically: atmospheric composition. By digging up and burning vast quantities of fossil fuels, releasing fossil CO2 into the atmosphere, we've been acting like a giant super-volcano.

Tyndall reported in 1861 that carbon dioxide blocks thermal radiation. The CO2 molecules absorb thermal radiation and re-radiate it in all directions, so some of it goes back downward towards the earth.

You can measure this in a lab, as Tyndall did, by shining infrared through a vessel of CO2. You can see it in the atmosphere: we have satellite measurements showing that outgoing thermal radiation has declined since 1970.

So incoming energy > outgoing energy. Additional heat accumulates until a new, higher equilibrium temperature is reached.

It takes a long time for the actual temperature to catch up with the equilibrium temperature. (Tyndall: the atmosphere acts like a dam thrown across a stream, the water rises behind the dam until it reaches the top.) So even if we could stabilize the current CO2 level today, the temperature will continue to rise.

Novak's argument that CO2 molecules are too diluted to have a significant effect is incorrect. By reducing outgoing thermal radiation, the elevated CO2 level increases the equilibrium temperature at which incoming energy is balanced by outgoing thermal radiation. It has nothing to do with the temperature of the CO2 molecules themselves.

Because there's lots of random variation in temperature across the earth, what we see isn't a small uniform rise in temperature. Instead we see local or regional heat waves which are far hotter than in the past, like the 2003 heat wave in Europe which caused 70,000 premature deaths. For a more detailed view of the evidence of heat waves, see Hansen Sato Ruedy 2012. Figure 3 is especially remarkable.

Policy implications.

  • The part of this answer that says "we have satellite measurements showing that outgoing thermal radiation has declined since 1970" is incorrect. The linked source took Fig. 1c. of Harries et al., which is captioned "component of simulated spectrum due to trace-gas changes only". The actual data is Fig. 1b. which shows an increase in outgoing radiation throughout the ~730-1030 range. nature.com/nature/journal/v410/n6826/pdf/410355a0.pdf – DavePhD Jun 2 '17 at 10:55
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It has been amply demonstrated that global warming is in fact happening, e.g. http://data.giss.nasa.gov/gistemp/graphs_v3/ Therefore it can't be impossible :-)

The mechanism by which it happens has been known since the early 20th century: http://earthobservatory.nasa.gov/Features/Arrhenius/ The predictions of climate models are reasonably close to what is actually measured, e.g. http://www.nature.com/nclimate/journal/v4/n9/full/nclimate2310.html

  • "in theory, practice is the same as theory; in practice, they are different" comes to mind – Sklivvz Dec 10 '16 at 6:45
  • @Sklivvz: I think you need to explain that comment a little, because in practice what's predicted by theory/models is indeed reasonably close to what's observed. And the predictions get better when more accurate input data becomes available... – jamesqf Dec 11 '16 at 18:41
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    Absolutely -- I was referring to Gary Novak's theory being disproven by the simple fact that climate is warming. – Sklivvz Dec 11 '16 at 20:11
  • The general mechanism by which warming happens isn't disputed much even by most climate skeptics. But whether existing models give good predictions is widely disputed even by some non-skeptics. Though the nature article you quote argues models are good, it does so because several mainstream scientists have argued the opposite. We can hardly consider the issue resolved (however irrelevant to the question here). – matt_black Dec 12 '16 at 17:38
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    @matt_black wrote "Complex models (not just climate models) make people overconfident about uncertain predictions." this comment is suggestive of a lack of familiarity with what climate models actually show. The spread of the model runs from climate models is quite broad (and understood to be an underestimate of the true uncertainty). The point is that action on climate change is justifiable even taking that uncertainty into account. If you want a very clear example of models under-estimating climate change, try arctic sea ice extent (realclimate.org/images/seaice10.jpg). – Dikran Marsupial Jun 2 '17 at 18:13

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