Why is Venus hotter than Mercury etc.

[neilzero]

Likely some of the details, even the mainstream thinking will change, and still be wrong after the change. My math does not go much beyond high school, so I often cannot check the work of the experts, so I don't know what will change, but there does seem to be suspicious comparisons. Please correct my tentative assumptions:
The moon likely has and had little effect on green house warming the past 3.6 billion years. Earth has always had some green house warming, otherwise it would be almost as cold as Mars is now. My guess is more green house gas might warm Earth 9 degrees f = 5 degrees c, but not much more, unless the atmospheric pressure increases drastically as at Venus which has about 90 times more atmosphere than Earth. I have not seen a graph or chart that shows the the amount of green house warming that results from higher atmospheric pressure, but I am quite sure Venus is hot, partly because it has a thick atmosphere. My guess is neither Earth nor Venus ever had "run away" green house warming of significance, as the hockey stick graph has been discredited in my opinion, but some positive reinforcement occurs.
No fossil evidence has been found for ice age at Earth the first 3.6 billion years = all the ice ages have occurred in the most recent one billion years, and only about half of Earth's surface was covered by the worst ice caps.
This is surprising, as the Sun produced only about half as much energy 4 billion years ago. This is the result of nuclear fusion math and theory, which was sufficiently correct to produce reliable fusion = H bombs.
It is difficult to measure, with extreme accuracy, the distance to the sun, because the surface is very hot plasma, but some reports of Earth moving a few millimeters per year away from the Sun have not be debunked as far as I know. A few billion millimeters does not put Earth lots closer to the Sun, but it could account for no ice ages the first 3.6 billion years. The recent recession from the Sun, if real, may be a recent change, but there is little reason to think the recession rate has changed much over the past 3.6 billion years. Some of this may be creationist's pseudo-science. Neil

[Shaula]

Venus is hot because it has a thick atmosphere made up of carbon dioxide and lots of sulphur dioxide clouds. Density is only part of the issue, composition is very important. The runaway effects of water vapour are why it ended up where it was. There was an ice age about 2.5 to 3 billion years ago. The Sun was though to be about 70% of its current brightness, not 50%. Google Snowball Earth to see that it is likely that most of the Earth's surface froze.

Need to do some more background reading on this - I'd suggest you read up on atmospheric physics and some astronomy books on planetary evolution.

[John Jaksich]

Although it has been approximately worded as a run-away greeenhouse effect----one approach to learning about subjects that you speak of is to pick a book (or a good vid on the subject)---despite the seemingly large selection of Intro. Astro textbooks (and may serve you best) start with a good popularization such as ----Neil Comins ------> What if the Earth had Two Moons or Heavenly Errors

That approach (IMHO) will help to nurture (?) your mind ----rather saturate it with too many facts.


As Einstein said---it is the ability to imagine that may serve to ultimately answer your questions and not so much to utter facts, only.

[lomiller1]

The “run away” greenhouse effect of Venus is referring to the fact it’s surface temperature is too high to form carbonate rock meaning all its CO2 ultimately ended up in the atmosphere. If the earth was to warm to the point where it’s carbonate rock broke down we’d have similar amounts of it in our atmosphere.

Pressure is a red herring. Atmospheric density plays a big role in how energy gets distributed though the atmosphere but can’t change the energy balance of the atmosphere. Conservation of energy requires that the amount of energy leaving the top of the atmosphere be in balance with the non-reflected sunlight entering the top of the atmosphere.

Assuming the later is roughly constant, you get a fixed value for IR existing the atmosphere which in turn gives you a fixed blackbody temperature. Pressure/density does nothing to change this balance meaning it can’t change surface temperature. Greenhouse gasses on the other hand intercept outgoing IR, which means more IR needs to be emitted to maintain the TOA energy balance and more initial IR corresponded to a higher black body temperature. If there were no greenhouse gasses in the earth’s atmosphere it would be at its blackbody temperature or ~34 deg C colder . (Technically planets are not quite black bodies but are close enough.)

[Shaula]

The density of an atmosphere affects the amount of said greenhouse gases along a given path length so it does have an effect AIUI. The oh so promising but ultimately misleadingly named Beer's law.

[transreality]

No fossil evidence has been found for ice age at Earth the first 3.6 billion years = all the ice ages have occurred in the most recent one billion years, and only about half of Earth's surface was covered by the worst ice caps.

Huronian Glaciation, the great oxygen catastrophe triggered by the oxdisation of atmospheric methane. 2100-2400Myr. Until destroyed by life, methane was acting as a greenhouse gas on earth.

[ArgoNavis]

Venus is hot entirely due to a thick atmosphere, or perhaps more correctly, high atmospheric pressure. The calculations are here. Anyone who considers the "greenhouse" effect to be real, please show how this argument is in error.

Using the same calculations, I can determine that Earth receives 1.23 as much radiation as Mars, and at 10mb (surface pressure on Mars, pressure at 68,000m on Earth) the standard temperatures of -63C for Mars and -52C for Earth mirror that physical relationship.

[lomiller1]

Venus is hot entirely due to a thick atmosphere, or perhaps more correctly, high atmospheric pressure. The calculations are here. Anyone who considers the "greenhouse" effect to be real, please show how this argument is in error.

Wow what a bad link. First of all Venus receives slightly less solar energy then the earth because it's more reflective. Second as I said above the as I said above, there is no mechanism for atmosphere pressure to retain heat, therefor a surface temperature different then black-body temperature is impossible because it would violate conservation of energy. Third the "formula is just random calculations with no particular rational behind them. Forth it falsely assumes there is a fixed relationship between pressure and altitude, there isn't. An atmosphere will expand/contract with temperature changes and temperature at any given altitude is a function of surface temperature and lapse rate.

[Shaula]

Anyone who considers the "greenhouse" effect to be real, please show how this argument is in error.

Nope. Greenhouse effects are scientific mainstream. The challenge is for you to prove that it doesn't work (and this is not the forum to do that). If you succeed then let me know. I'll happy change my responses on here and buy you a drink to celebrate your Nobel win.

[lomiller1]

Some approximate calculations below: (feel free to correct any calculation errors I did this pretty quickly)

Incomming solar energy
Venus - ~2500 W/m^2
Earth - ~1350 W/m^2

But since sunlight comes from a single direction, you need to divide by 4 to get average insolation
Venus - 625 W/m^2
Earth - 338 W/m^2

The earth reflects 30% of the sunlight it receives while Venus reflects 75%
Venus - 156 W/m^2
Earth - 236 W/m^2

This is how much energy is entering each planets respective atmosphere per m^ each second. As you can the earth is actually receiving considerably more energy despite the fact Venus is much hotter.

Now lets look at surface temp

Average surface temperature
Venus 700 deg K
Earth 290 deg K

At these temperatures you get blackbody radiation of
Venus – 700^4 * 5.67*10^-8 = 13 000 W/m^2
Earth - 290^4 * 5.67*10^-8 = 400 W/m^2

In both cases the surface of the planet is emitting more energy in IR then the planet itself is receiving from the Sun. In the case of Venus much much more. But since neither planet is warming very much we know that this IR doesn’t all escape the atmosphere. Atmospheric Pressure mass, atmospheric, density, thickness etc cannot explain this, the only way this can happen is if this IR is being absorbed by the atmosphere before it can get into space, and gasses which do this are by definition greenhouse gasses.

Lets assume nitrogen doesn’t absorb IR at all at this frequency, which isn’t entirely true but it absorbs very little. If you had an equally dense atmosphere made entirely of nitrogen all the emitted IR would escape into space and the planets surface temperature could not rise above the point where blackbody radiation matched incoming solar energy. In all likelihood with an atmosphere at thick as Venus even nitrogen would absorb some IR but it would be much less then what a CO2 atmosphere does and therefore surface temperature would have to be much lower than Venus currently has.