Friday, December 22, 2017

Why Nikolov and Zeller's Pressure Claim Violates Basic Physics

Nikolov and Zeller claim that planetary surface temperatures are set by surface pressure. Published in a journal indicted for fraud.

They even go so far as to assert that there is no greenhouse effect. Or that it's 90 K, not the usual 33 K we have all seen. (Which, by the way, is a heuristic calculation only.) Hard to keep their claims straight.

This is obviously bull -- but why?

Because N&Z did no science -- they just fit 5 independent data points to a curve of 6 independent data points. Just curve-fitting.

I trust you understand why that's trivially easy to do, and why it's not science.

But they insist they have made a ground-breaking discovery, a la Galileo or Newton.

(That should set your bullshit detector off right there, ringing very, very loudly. See John Baez's Crackpot Index.)

But here's the thing -- their claim isn't even in accord with basic physics.

Their formula for surface temperature as a function of surface pressure, Ts(Ps), implies, for current Earthlike conditions

dTs/dPs > 0
where "s" stands for surface.

But this is wrong, for the simple reason that a higher surface pressure leads to a lower surface temperature. And it's not difficult to understand why.

It comes down simply to density and optical path. More pressure means more molecules in the path of incoming sunlight, which means less sunlight reaches the surface, because there is less shortwave (Rayleigh) scattering. From Poulsen et al, Science 2015:

Click to Enlarge

So lower pressure means less scattering of sunlight, so more of it reaches the surface. The surface is warmer at lower pressure. That's not surprising -- though N&Z choose to turn their back on this physics.

And a warmer surface means a higher temperature in the lower troposphere, which in turn means the air holds more water vapor. (See the Clausius-Claperyon equation.) That water vapor increases the greenhouse effect, leading to an even higher surface temperature.

So the idea that pressure somehow creates a higher surface temperature is clearly wrong. Atmospheric pressure does not increase incoming shortwave radiation -- radiation from the Sun. It decreases it.

Naturally (and unfortunately), Nikolov and Zeller have ignored all questions about this on Twitter, as if they think blatantly ignoring these question about the physics will get rid of these inconvenient questions, and their stolid, unenlightening, unphysical curve-fitting will shine through.

This is why they're properly classified as "deniers." Real scientists and real people do not ignore questions, if they're interested in getting at the truth.

If you don't want to be labeled a denier, don't act like one.

1 comment:

Thomas Palm said...

If you stick to the idea of N&Z that there is no greenhouse effect your claim that more atmosphere would lower surface temperature has some merit. Once you include the statement about water vapor as a greenhouse gas it falls apart, however. Greenhouse gasses are more effective at higher pressure due to pressure broadening of the absorption lines, so with more atmosphere you will have a thicker layer where they are efficient at absorbing IR, and since the temperature gradient is limited by onset of convection a thicker absorbing layer correspond to a higher surface temperature.

Here is an interesting problem I just thought of. Assume Venus had the same amount of atmosphere as today but that almost all of it was perfectly transparent except for the same amount of CO2 as can be found on Earth. How strong would the greenhouse effect be?