One big premise for the Green New Deal is that Venus's atmosphere is a "runaway greenhouse" due to its atmospheric composition being largely carbon dioxide gas, which absorbs the outgoing infrared radiation from the surface, thereby retaining the heat from the incoming sunshine.  This blanketing effect is said to be so effective that the surface temperature of Venus is hot enough to melt lead.

But has anyone ever compared Venus's atmosphere to the Earth's with the goal of testing this assumption?  Let us do just that using established physical laws.  I propose to use Gay-Lussac's Law as our starting point.  It states that the absolute temperature and pressure of an ideal gas are directly proportional, under conditions of constant mass and volume.

We start with the fact, established by NASA, that the surface pressure on Venus is 93 times that of the Earth.  Since pressure is measured with respect to a fixed surface area, typically per square inch, the one-inch cube of gas at the surface of Venus would be much, much hotter than the similar cube at the surface of the Earth — ninety times hotter for an "ideal gas."  Carbon dioxide is not an ideal gas, but clearly the much higher surface pressure should result in a much higher temperature.  Due to the higher pressure, we expect Venus to be hotter than the Earth.  This would be true regardless of the solar input.  Moving Venus out to the orbit of Mars would not change the mass of the atmosphere or the acceleration of gravity, so simply the compression of the gas results in a high surface temperature.

Let us try a thought experiment based on Earth's atmosphere.  Let us imagine that a passing comet's tail is drawn into our atmosphere.  Let us assume it is 78% nitrogen, 21% oxygen, and 1% argon, and the mass of the gases drawn in is equal to the mass of Earth's current atmosphere.  In effect, we have doubled the mass of the atmosphere, and therefore the surface pressure, without changing the greenhouse gases.  The "greenhouse effect" would be unchanged.  But Gay-Lussac's Law tells us that the surface temperature would soar.  You do not need a "greenhouse effect" to get a higher surface temperature.

If our insight is correct, what would we expect to see in reality?

1. We would expect the temperature to decrease with increased altitude and therefore pressure.  That is known as the adiabatic lapse rate.  Even a kid with a window seat on an airliner can feel the window get cold as the plane increases its altitude.  Given the task of drawing a tall mountain, the child is likely to put a glacier at its peak.  If he were to fly to South America, over the country of Ecuador (derived from "Equator"), he could see its seven glaciers.  Glaciers at the Equator?  Who knew?  The summit of the tallest, Chimborazo, "despite not being the tallest mountain in the Andes or on Earth ... holds the distinction of being the farthest point on Earth's surface from the Earth's center, due to its location along the planet's equatorial bulge.  Chimborazo's height is 6,263 m (20,548 ft), well below that of Mount Everest (8,849 m)."  Given that the local gravitational force is inversely proportional to the square of the distance between the centers of gravity (Newton's law of gravitation), it would have the lowest surface pressure on Earth.  Therefore, it would be quite cold — cold enough to maintain a glacier about 102 miles south of the Equator.  It is located at 1° 28′ 9″ S, 78° 49′ 3″ W; -1.469167, -78.8175.
2. With the approach of the autumnal equinox on Earth, it is also interesting to note that while Earth has glaciers at each pole, Venus is believed to have a fairly uniform surface temperature, even on the dark side and at the poles.  This makes sense if the temperature is determined by the pressure, but not based on insolation.  Caltech gives the length of a Venusian day at 5,832 hours contrasted with our 24-hour day.  To put that in context, the Venusian night is half that, or 122 Earth days long.  Its night is four months long, yet the temperature does not decline significantly?  That makes no sense.  Only a Green New Dealer who thinks solar panels are the solution to our energy future would believe that.

Let us consider other terrestrial bodies' surface temperatures.

Mercury is closest to the Sun and gets the strongest sunlight, but it is cooler than Venus due to its low gravitational force and low surface pressure.

The Moon gets the same insolation as the Earth, being at the same average distance from the Sun, but is much colder.  It has little atmospheric pressure and a lower gravitational force.

Mars has a carbon dioxide–rich but very thin atmosphere with less gravity than Earth and is therefore much colder.

There is a good correlation between a planet's surface pressure and temperature.  QED.

Image via Raw Pixel.