Michael Way, Richard Ernst, and Jeffrey Scargle say maybe:
Large scale volcanism has played a critical role in the long-term habitability of Earth. Contrary to widely held belief, volcanism rather than impactors have had the greatest influence on, and bear most of the responsibility for, large scale mass extinction events throughout Earth’s history. We examine the timing of Large Igneous Provinces (LIPs) through Earth’s history to estimate the likelihood of nearly simultaneous events that could drive a planet into an extreme moist or runaway greenhouse, quenching subductive plate tectonics. This would end volatile cycling and may have caused the heat-death of Venus. With a conservative estimate of the rate of simultaneous LIPs, in a random history statistically the same as Earth’s, pairs and triplets of LIPs closer in time than 0.1-1 Myrs are likely. This simultaneity threshold is significant to the extent that it is less than the time over which the environmental effects persist.
I haven’t looked at the actual paper—it seems that they do some time series analysis; what I really wanna see is some sort of scatterplot—but it’s an interesting hypothesis, that’s for sure!
They could be right but that doesn’t mean the mechanism is correct. I still haven’t seen an explanation for this:
https://physics.stackexchange.com/questions/508573/why-does-this-simple-equation-predict-the-venus-surface-temperature-so-accuratel
Tldr:
Surface yemperature seems to be determined by distance from the sun, thickness of atmosphere, and mass of the planet/moon. Everything else (albedo, composition, etc) cancel out as the atmosphere seeks out an equilibrium temperature.
Or I guess it is a coincidence.
Wow, they took the standard thermodynamic black-body relation for T given a hot neighbor:
T scales as d^(-1/2),
threw in fudge factors (picking a starting atmospheric height and then counting down) and managed to fit 3 selected points, with only one of them done by definition! Very impressive.
p.s. It’s not “equilibrium”. It’s steady-state. If you can keep it.
That isn’t what they (*I) did at all. It is so funny how religious people are about this stuff, you had no reading comprehension at all. Your mind just blanked out.
Anyway, no further data is incoming unless/until mars gets terraformed to have an atmosphere thick enough for a troposphere (~200 mbar). Then we’ll have 4 datapoints.
In a sense, that calculation is implicitly taking the standard greenhouse effect into account. The thing to consider is why are the conditions at ~50km on Venus similar to those of the Earth (approximately)? The answer is essentially because the runaway greenhouse effect has pushed the effective radiating layer in the atmospher up to an altitude of 50 km. Rather than the energy being radiated from the planet to space coming directly from the surface it comes (on average) from an altitude of 50 km. To be in energy balance, the effective temperature at that altitude has to be similar to that of the Earth (I get ~233 K for Venus’s albedo, but maybe I made some mistake). If you then work down the lapse from 50 km to the surface, at ~10 K/km, you get a surface temperature that is about 500 K higher than the temperature at ~50 km.
I realise I should have said “similar to those of the Earth (approximately) when scaled by distance”.
It assumes whatever processes are going on in the Earth atmosphere to determine the long term average surface temperature are also going on in similar atmospheres. We only have Venus and Titan since none of the other rocky planets/moons have enough atmosphere for a troposphere. And the gas giants are gas giants.
So it is perfectly consistent with a greenhouse effect, but the vastly different compositions of the three atmospheres indicate that other factors such (eg, albedo) will adjust in response to maintain an equilibrium or attractor state.
Really seems like a coincidence to me. Why would the blackbody radiation equilibrium determine temperature at a particular pressure? Physically, that relation is about temperature of the radiating/absorbing body. And by the principles of this equation, you’d be able to use it to predict temperature at multiple altitudes not just the surface. But if you increase the altitude at all on Titan, the numbers go all wonky. At the very least, you should be accurate at your 1 atm fixed point, not just at the surface after the lapse rate scaling.
The Titan data doesn’t seem very accurate yet. AFAIK there is only Cassini measurements for only about half a Saturnian year. Really the values should correspond to a multi-year average.
I would assume the surface temperature is the best value we have but even there now it says on wikipedia:
https://en.wikipedia.org/wiki/Climate_of_Titan
When the post was made in 2019 it read:
That is why I felt comfortable using wikipedia numbers rather than a primary source. But actually a prediction this model makes is that (if the pressure is indeed 1 atm at ~ 10 km altitude on average) the lapse rate in the troposphere is closer to 0.2 K/km rather than the 0.6-0.7 K/km currently estimated. Alternatively, the 1 atm altitude could be higher.
Venus is bone dry, so scaling Earth’s dry lapse rate by g is a good approximation. For Earth, the difference between dry and moist lapse rate makes a big difference, so picking some other pressure could give wonky answers for Earth. This might also apply to Titan, where methane is near the triple point.
Another thing I wonder about is how accurately that “typical” lapse rate really describes the long term average, in particular near the surface where inversions are quite common.
I couldn’t find a single source for a good summary but saw many papers describing ~50% of days had inversions with duration of at least a few hours and intensity around 2-5 K. This varied by time of day, season, and location of course… So perhaps for a long term average the dry lapse rate ends up being more accurate. At least for the surface.
>Everything else (albedo, composition, etc) cancel out as the atmosphere seeks out an equilibrium temperature.
Ah, an absurd conclusion supported by nonsensical physics-y argument, like talking about a non-equilibrium system as if it “seeks out an equilibrium”. Funny that you would comment “how religious people are about this stuff” in the follow-up. As if your religion-like disbelief in the greenhouse effect could make real physics go away.
I came up with a small set of plausible assumptions and derived a quantitative model without any free parameters. It fit the current data surprisingly well.
I agree it could be a coincidence, we need more data to check the prediction.
That is how science works.
It is quite possible some readers of this blog have never been exposed to actual science, and simply do not comprehend it.
What do the authors mean by “heat-death” here? The heat death of the universe is when the universe reaches thermodynamic equilibrium and temperature differences cannot be used to do work. I do not think this has happened on Venus.
I work in planetary science, but I have not heard the phrase “heat-death” applied to planets. However, I don’t study Venus, so it might be a common term in that community. That said, I believe they are implicitly assuming that a planet is dead when it is not longer potentially habitable. So, for this paper, they are arguing that volcanism, under the right conditions, would have baked out the upper crust, put the evaporated water in the atmosphere which would trigger a runaway greenhouse, i.e., a hot climate, and eventually all of the atmospheric water is lost to space leaving a hot climate ever after. This hot climate would be your dead Venus. Thus, the volcanically induced heating leads to the “death” of Venus.
Interestingly, Sean Raymond has a series of posts on how planets die: https://planetplanet.net/2019/02/04/how-planets-die/ There’s probably more thoughts on this topic there.
> Venus is bone dry, so scaling Earth’s dry lapse rate by g is a good approximation.
Well no, as the lapse rate does naturally depend on the composition of the atmosphere.
For the adiabatic rate, it is simply inversely proportional to the heat capacity Cp.
While the heat capacities of nitrogen and CO2 (the main components of the respective atmospheres of Earth and Venus) are not hugely different, they do deviate more than the gravities of the two planets.
In any event, the suggested calculation is physically nonsensical. It is not the surface that is heated by the atmosphere, governed by the lapse rate. Rather the situation is the reverse: the lapse rate describes the gradient of the rising gas as its ascends from the surface that heats it.
None of this is assumed to derive the calculation. I simply assume *it works on other rocky planets with a troposphere the same way it works on earth*. The derivation is shown step by step.
What exactly that entails is left open, for the sake of the model that is hypothesis non fingoed.
However, I did fingo a hypothesis. If it turns out that the composition of the atmosphere indeed can be largely ignored, one plausible explanation is that the composition is not independent of the albedo and other such factors. I.e., you can’t get a stable system by changing one without the others.
> If it turns out that the composition of the atmosphere indeed can be largely ignored
But it cannot be. One of your fudge factors, the lapse rate, is directly affected by the composition.
As I mentioned above, there are inversions, etc. Then even on the wikipedia page they list 9 variables contributing to the lapse rate: https://en.wikipedia.org/wiki/Lapse_rate
But anyway, it does indeed lead to some otherwise surprising conclusions in the vein of lakatos’ progressive vs degenerating research programmes concept. We need to see how the predictions play out.
> Then even on the wikipedia page they list 9 variables contributing to the lapse rate
Funny that you should mention that. The wikipedia (as well as primary sources) tell you right there that, even over Earth, the atmosphere does not have “the lapse rate” as a single well defined quantity: even the simplified abstract ISA lists 7 vastly different ones (some zero, some with inverted sign).
https://en.wikipedia.org/wiki/International_Standard_Atmosphere
Yet you feel confident to transfer the one value picked as a reference value over to other planets, with different atmospheres (and meteorology, which also play an important role, alas). Adding an un-physical scaling relation to it, even.
There is nothing scientific about your equation, really.
The earth doesn’t have a single well defined temperature either. These numbers are all abstract long term approximate averages.
I can see nothing productive is happening here, so I’ll leave it at that.