New find of 100+ exoplanets suggests Earth-like planets might be present

So there must also be a planet, after a few narrow escapes, chock-full of dinosaurs who discovered how to make musical instruments from the remains of ammonites. No need to communicate with us anymore.

I would argue that it is not the pressure itself, but the sheer amount of that atmosphere which is responsible. Consider that while increasing pressure from some starting point does increase temperature (all other things being equal), Venus has had billions of years to lose the excess heat produced by any such “pressurizing” event(s). Since it is likely that atmosphere has had its present thickness since it formed, no such pressurizing events are likely to have occurred, so pressure in & of itself is probably not the cause.
That said, while it is possible that the planet is a few degrees C warmer than it would be otherwise because of its ~95% CO2 content, I doubt that even swapping it out entirely for some other clear gas would make much of a difference. In other words, neither composition nor net pressure are likely to be the culprits responsible for making the night side of Venus hotter than the day side of Mercury.
Instead the extreme thickness of the atmospheric blanket itself seems to me to be the most likely reason for Ishtar’s extreme heat. To illustrate, our Terran atmosphere is ~75% N2, while the same element is only a trace gas making up ~4% of Ishtaran air. However, there’s enough of that trace N2 in the Venusian atmosphere to replace all of the N2 in Earth’s atmosphere ~3-4 times. And just as Earth’s air keeps our temps warmer and more stable than they would be without an atmosphere, so too does Venus’ air keep its temperatures MUCH warmer, and MUCH more stable than they would be otherwise.

So what is the density of Venus atmosphere at the solid surface ? At 90 atmospheres pressure, and common gases (presumably) the atmosphere must be quite dense.
g

“The density of the air at the surface is 67 kg/m3, which is 6.5% that of liquid water on Earth. The pressure found on Venus’s surface is high enough that the carbon dioxide is technically no longer a gas, but a supercritical fluid.”
Wikipedia

@jim G1: I once had the same understanding you do, Jim G1, and it took none other than an atmospheric scientist of the caliber of Roy Spencer to walk me through it. I didn’t change my mind because HE said it; I changed my mind because he presented the facts to me in a way that A) I could understand, and B) was in conflict with that old viewpoint. So I get where you’re coming from.
Those are ideal gas formulas for relating temperature, pressure & volume that you’ve presented, so allowing for the use of “ideal” gas laws in the current (very much NON-) ideal scenario, if one sets delta-T= 0K, does the pressure change (one way to look at the “in situ” hypothesis)? No, because zero times any number is still zero, which means the pressure has always been that high and no temperature change was needed to put it there. Further, if one chooses a non-zero starting value for T but a high starting value for P (e.g., one similar to Venus’ current surface pressure, another “in situ” look), then since there is little or no delta-P, there is also little/no delta-T. In other words, if either the temperature OR the pressure have always been what we see currently, then gas laws alone can’t explain what we’re seeing.
The only remaining scenario where pressure appreciably affects the temperature of Venus’ atmosphere, then is where one chooses a non-zero starting value for T (reasonable given proximity to the sun) and a significantly high value for delta-P (not UN-reasonable, as the gas may have collected over time). This results in a high delta-T due to delta-P, as you’ve intuitively gathered. However the question in this case is not, “Does an increase in pressure create an increase in temperature?” Of course it does! The key question is, “Does the resulting increase in temperature stick around in perpetuity, or does it eventually escape to space?”
Since the postulated pressurizing event happened only once (whether instantly or over a period of time), & since that impulse has never been replenished (solar heating & geothermal cooling having been relative constants throughout this time), as all other impulse heating eventually escapes unless replenished from some repeating or continuous source, we must assume that this heat is also eventually lost according to the laws of thermodynamics. Thus it is simply a matter of determining whether any of the impulse of heat from that initial pressurization has remained trapped since that event, or whether the heat has had time to escape to space.
If one does the math to show how all of that Venusian gas gains in temperature from near-vacuum in Venusian orbit to 90+ bar (assume if you like that the entire atmosphere attains the current surface pressure), then calculates how long it would take to lose that same heat to space before regaining radiative balance per applicable black-body equations, it becomes clear that all of the heat of compression is lost within a few centuries to a few hundred millennia (say 1,000 – 1,000,000 years, give or take, relative to the starting assumptions values, and thus ending values, which may vary significantly). But since the solar system formed billions of years ago, none of that heat from compression can possibly remain today. As such, what is left must necessarily be due to the current balance between solar radiation (etc.), and the radiative losses to space.
To illustrate this principle in a more everyday way, consider that every aerosol can in one’s house stores gases under extreme levels of pressure, and that the ideal gas laws apply to them just as much as to any other gas. So why isn’t the tank of propane (e.g.) feeding one’s barbeque — or the can of mosquito repellent, or the can of non-stick cooking spray for the grill & grilling utensils, etc. — too hot to touch without asbestos gloves? Because the excess heat generated during the compression of the gas while squashing it into its current container has had more than enough time to achieve thermodynamic equilibrium with its immediate environment, that is, to equalize in temperature with the surrounding environment. In fact, it equalized long before it went into storage before heading to market. As a result, your can of now-compressed gas is the same temperature as the surrounding environment regardless of the pressure of the gas inside it, and will remain so until either the pressure is relieved (cooling) or more gas is added (heating). Put even more simply, if one uses an hand-held air-pump to pressurize a bike tire or sports ball, the compression tube will heat significantly… but it does not stay hot forever. Granted the tube is nowhere near the size of a planet, and ideal gas laws don’t apply cleanly to a metal container with a compressed gas inside, but neither do they apply cleanly to a planetary atmosphere whose pressure changes both intrinsically & significantly with altitude, and is which is in direct contact with both a planet & the vacuum of space.
The mystery that planetary science has yet to solve is whether Ishtar (aka, Venus) is mind-meltingly hot (again, hotter than Mercury, and — more mysteriously — ridiculously uniform in its surface temperatures) because CO2 traps more than its fair share of that solar radiation, or whether it’s simply because ANY similarly thick atmosphere would naturally trap a similar amount of heat energy before attaining equilibrium. I lean toward the latter explanation at this time, but am willing to be persuaded.