Is there a Greenhouse Effect on Venus?
An alternative way to describe long-term planetary temperatures raises profound questions about the role of greenhouse gases in the climate system
‘‘…as predicted by Ideal Gas Law, the Venusian surface temperature is determined by the weight of its atmosphere combined with it’s distance from the sun.’’
This one is really going to blow your mind!
Thanks in advance for reading, and as ever I look forward to your thoughts and comments.
Overview
Venus is hot! More than double the Earth’s temperature.
Given the high levels of carbon dioxide in Venus’ atmosphere, its’ high temperature is often used as an example of an extreme greenhouse effect.
But what if it turns out that the temperature of Venus is not linked to carbon dioxide concentrations?
A much simpler way of calculating long-term temperatures of planets has been proposed, based on tried and tested principles of thermodynamics.
Here we discuss this alternative concept, how well it stands up to scrutiny, and its’ implications for greenhouse theory.
‘Hot enough to melt lead’!
‘‘Venus today is a hellish world. It has a crushing carbon dioxide atmosphere 90 times as thick as Earth’s... Temperatures reach 864 degrees Fahrenheit (462 degrees Celsius) at its surface.’’ NASA
‘‘For a really strong greenhouse effect, we should look at Venus. Venus is similar to Earth in terms of size and mass, but its surface temperature is… hot enough to melt lead! The Venusian atmosphere is mainly made up of carbon dioxide...’’ European Space Agency
These quotes from two of our leading space institutions leave little room for doubt as to the cause of the extreme heat on Venus!
Similarly, my fellow environmental scientists that I talk to often use Venus as the ultimate validation of the Greenhouse Effect… how else could Venus be so hot?
It turns out that there is another, simpler explanation.
An explanation that doesn’t invoke carbon dioxide, or any other greenhouse gas for that matter, that removes reliance on ‘questionable’ thermodynamics, a topic about which I have written recently.
Ideal Gas Law
Many of my peers who have, for example, worked to help minimize air pollution from industrial facilities as I have done for two decades will be familiar with the principles of the Ideal Gas Law.
‘‘Principles of the Ideal Gas Law are used in countless engineering applications to help us produce many of the things in society that we rely upon and take for granted. In other words, they work!’’
The Ideal Gas Law mathematically describes, among other things, the relationship between the pressure and temperature of a gas or mixture of gases.
A quick math lesson!
The following Ideal Gas Law equation illustrates the relationship between pressure ‘P’ and temperature ‘T’ (‘V’ is the volume of the gas, ‘n’ is the amount of substance, and ‘R’ is a constant):
PV=nRT.
This equation describes the principle that if you increase the pressure, the temperature will also increase, all other things being equal.
But are all other things equal?
One way to increase the pressure of a gas might be to compress it into a smaller space, thereby simultaneously reducing its’ volume.
In this case, as pressure goes up, volume goes down. If this relationship were ‘linear’, or ‘proportional’, then compressing a gas wouldn’t actually increase it’s temperature, according to the Ideal Gas Law equation.
But this wouldn’t align with our real world experiences, so something must be missing.
As described by another simple law, Boyle’s Law (itself a precursor to the Ideal Gas Law), we know that the relationship between pressure and volume is not, in fact, linear:
P ∝ 1/V
(where ∝ means ‘inversely proportional to’)
This equation describes in mathematical terms what you would experience if you pushed down on a sealed syringe filled with a fixed amount of air; the amount of force required to move the syringe the first cm is much less than the force required to move it the final cm.
Don’t worry, that’s enough math for one day! It is just important to understand that as the pressure of a gas (or mixture of gases) increases, it’s temperature will too. And this will continue be the case if the pressure is increased by virtue of the volume of the gas being decreased under compression.
(This is in fact the very same principle that causes ignition of the fuel/ air mix within a diesel combustion engine, for example.)
And this is the starting point at looking at an alternative method of calculating the temperature of Venus’ atmosphere. The atmosphere being the gas, or mixture of gases, that we looked at with respect to the Ideal Gas Law.
Applying pressure to Venus
So if pressure influences temperature, what determines the atmospheric pressure of Venus?
Venus’ atmospheric pressure is a function of the mass of its atmosphere, combined with the force of gravity acting upon it*. Mass and gravity together determine an objects ‘weight’.
(*Gravity is dependent on the planetary mass from which it comes; the greater the mass of the planet, the higher the gravitational attraction).
So, along with it’s distance and therefore energy received from the sun, Ideal Gas Law allows us to calculate Venus’ surface temperature by virtue of the weight of its atmosphere.
This external energy amplifies the warming effect of the sun, and increases the temperature above that which would be observed if relying on the suns energy alone.
This leads us to a really quite profound proposition:
‘‘You don’t need to know anything about the chemical composition of Venus’ atmosphere to be able to derive it’s average surface temperature.’’
In other words, the long-term, average temperature of Venus has nothing to do with greenhouse gases!
Moreover, it turns out that you can calculate the temperature of all rocky worlds in our solar system, including the Earth, in a similar way.
Does it work?
pHD scientists Nikolov and Zeller published a paper in 2017 in which they developed a mathematical model based on the Ideal Gas Law principle. Their model reportedly performs very well for the rocky worlds in our solar system for which there is sufficient actual data (see the figure above) against which their calculations can be verified.
In their paper they explain how energy is being supplied to the system through the effects of gravity, and expressed as pressure.
The Nikolov and Zeller (NZ) paper is quite a lot to digest in full, but here is a very accessible YouTube video (albeit quite long) in case you are interested in learning more about their ideas.
A central objection to the NZ hypothesis is that the observed pressure increase on warmer planets is a result of temperature rise (presumably caused by the radiative properties of greenhouse gases), as opposed to a cause of it, a point raised by Cotton in his 2020 rebuttal, for example.
‘‘Equations such as the Ideal Gas Law don’t only work in one direction, and so this objection does stand up to some extent.’’
However, this objection doesn’t explain, among other things, why the NZ model performs so well across planets irrespective of greenhouse gas composition. And neither can it account for other temperature phenomenon which are well known to be pressure-induced such as adiabatic lapse rates.
Much more could be written about this ‘debate’, and I urge you to follow the links in this article to find out more.
Conclusion
This pressure-based approach of explaining the temperature of a planet utilizes concepts that are extremely well tried and tested in the real world. The concept is really quite simple:
‘‘There is nothing new about describing the relationship between pressure and temperature; my fellow atmospheric scientists will be well aware of the concept of ‘adiabatic lapse rate’, or heat-causing high-pressure weather systems, for example.’’
The proposition here is that we do not need greenhouse theory to explain the long-term temperature of the planet. This does still leave the door open as to whether greenhouse gases could ‘fine tune’ shorter-term temperature variations, and therefore still play a part in the climate system.
In response to this point, I would refer you back to my earlier article on The Climate Control Knob, which shows that the correlation between the Earth’s carbon dioxide and temperature isn’t at all convincing over geological time frames.
I hope you have enjoyed this article and if nothing else it has made my fellow atmospheric scientists brush up on their Ideal Gas Law, adiabatic lapse rates and high-pressure weather system definitions!
‘‘Remember, true science is about challenging consensus, not adherence to it.’’
Thanks for reading!
-Tristan
PS. For some very accessible background reading on Ideal Gas Law, Boyle’s Law and other related concepts related to the relationship between temperature, pressure and volume of gases as referenced in this article, I can recommend this course from the Lumen Learning website.