# How hot would Venus be without the greenhouse effect? **URL:** \ **Category:** Factual Questions\ **Created:** [August 6, 2013, 3:24pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497 "2013-08-06T15:24:26Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [August 6, 2013, 3:24pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/1 "2013-08-06T15:24:26Z")
If Venus didn’t have a very thick envelope of carbon dioxide- say it had 1 standard atmosphere of nitrogen- how hot would it be? ---
**Author:** ![aNewLeaf](https://avatars.discourse-cdn.com/v4/letter/a/ac91a4/32.png) [@aNewLeaf](https://boards.straightdope.com/u/aNewLeaf)\ **Post date:** [August 6, 2013, 3:44pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/2 "2013-08-06T15:44:32Z")
About as much hotter than Earth as Earth is compared to Mars, is my first guess. ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [August 6, 2013, 5:00pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/3 "2013-08-06T17:00:40Z")
An effective temperature (assuming Venus had an albedo of zero and no atmosphere) can be derived using the [Stefan-Boltzmann law](http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law), which is based on the assumption that the planet will absorb all solar radiation incident on it, and rise in temperature until the thermal radiation it emits is enough to dispose of all that power. Using the derivation that that article uses for the Earth, but with Venus’ numbers gives an effective temperature of about 329K (55.9 C). As is noted in the article, there is a downward adjustment for non-zero albedo, and and upward adjustment because of the atmosphere, but that gives a ball park estimate. ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [August 7, 2013, 12:34am UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/4 "2013-08-07T00:34:29Z")
Why is the Venutian atmosphere so dense? The earth is a lalrger mass than Venus-and our atmosphere is much thinner. Why hasn’t the Venutian atmosphere boiled off to space (and be about the same density as the earth’s). ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [August 7, 2013, 12:59am UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/5 "2013-08-07T00:59:07Z")
> [@ralph124c](#): > > Why is the Venutian atmosphere so dense? The earth is a lalrger mass than Venus-and our atmosphere is much thinner. Why hasn’t the Venutian atmosphere boiled off to space (and be about the same density as the earth’s). It is largely carbon dioxide, which is a much heavier gas than the nitrogen and oxygen that make up most of Earth’s atmosphere. If it wasn’t for plants eating up the CO2 and pooping out oxygen, our atmosphere would no be much different. ---
**Author:** ![smarter](https://avatars.discourse-cdn.com/v4/letter/s/9fc29f/32.png) [@smarter](https://boards.straightdope.com/u/smarter)\ **Post date:** [July 12, 2014, 6:49pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/6 "2014-07-12T18:49:24Z")
About 80 degrees celsius, or 353 degrees Kelvin. You do this by seeing how many times further away the Earth is from the sun. Then you take that number (1.38251), and multiply it by earth’s temperature if it didn’t have greenhouse gasses(255k). The answer is 353 degrees kelvin, or 80 degrees celsius. So if you are wondering the greenhouse gasses are responsible for making Venus 384 degrees warmer than it already is…now that is a hot topic:D ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 12, 2014, 8:43pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/7 "2014-07-12T20:43:02Z")
Venus actually has about the amount of atmosphere you’d expect for its mass and distance from the Sun. The better question is why Earth’s (and Mars’) atmosphere is so thin. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [July 13, 2014, 2:38pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/8 "2014-07-13T14:38:06Z")
> [@smarter](#): > > About 80 degrees celsius, or 353 degrees Kelvin. > > You do this by seeing how many times further away the Earth is from the sun. Then you take that number (1.38251), and multiply it by earth’s temperature if it didn’t have greenhouse gasses(255k). The answer is 353 degrees kelvin, or 80 degrees celsius. > > So if you are wondering the greenhouse gasses are responsible for making Venus 384 degrees warmer than it already is…now that is a hot topic:D This derivation doesn’t work, even in the absence of greenhouse gases. According to the Stefan-Boltzmann Law (mentioned upthread), the proportionality works out to (temperature in Kelvin)[sup]4[/sup] \* (radius of the planet)[sup]2[/sup] is inversely proportional to (distance from planet to star)[sup]2[/sup] for planets orbiting around the same star (and with the same albedo). For Venus and the Earth, the sizes of the two planets are about the same, so the temperature in Kelvin on Venus will be inversely proportional to the _square root_ of the distance to the Sun, not the distance itself. ---
**Author:** ![smarter](https://avatars.discourse-cdn.com/v4/letter/s/9fc29f/32.png) [@smarter](https://boards.straightdope.com/u/smarter)\ **Post date:** [January 3, 2016, 5:23pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/9 "2016-01-03T17:23:59Z")
Sorry about that my math was VERY flawed. Stephan Boltzmann’s law is the correct way to go about solving this problem. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 3, 2016, 5:48pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/10 "2016-01-03T17:48:56Z")
> [@smarter](#): > > Sorry about that my math was VERY flawed. Stephan Boltzmann’s law is the correct way to go about solving this problem. Yes, we owe all this to the hard work of Stephan, the brainiest of the Boltzmann brothers, and his graduate student Alphonse Bedo. ---
**Author:** ![lalaith](https://avatars.discourse-cdn.com/v4/letter/l/96bed5/32.png) [@lalaith](https://boards.straightdope.com/u/lalaith)\ **Post date:** [January 3, 2016, 7:09pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/11 "2016-01-03T19:09:58Z")
> [@njtt](#): > > If it wasn’t for plants eating up the CO2 and pooping out oxygen, our atmosphere would no be much different. Really? Do you know of an article (online) about this as I’d like to read it if it’s not too technical? ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [January 3, 2016, 7:24pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/12 "2016-01-03T19:24:14Z")
Depends which Venus. The one from Milos would be smokin’ hot whether or not she’s standing in a greenhouse. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 3, 2016, 8:32pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/13 "2016-01-03T20:32:11Z")
You’ve got to respect the dedication of a guy who will come back to a thread a year and a half later to admit he was wrong. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 3, 2016, 8:40pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/14 "2016-01-03T20:40:06Z")
> [@Chronos](#): > > You’ve got to respect the dedication of a guy who will come back to a thread a year and a half later to admit he was wrong. Cooling off period? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [January 3, 2016, 9:22pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/15 "2016-01-03T21:22:41Z")
A similar question is asked and answered on this page [http://m.teachastronomy.com/astropedia/article/Venus-and-the-Greenhouse-Effect](http://m.teachastronomy.com/astropedia/article/Venus-and-the-Greenhouse-Effect) > [@](#): > > A useful trick in this kind of calculation is to divide the second equation by the first, so that we deal only with the ratios of the quantities that are changing, and the constants of proportionality cancel out. Then we get: > SVenus / SEarth = (TVenus / TEarth)4 > From the discussion above, we know that the quantity on the left side, i.e. the ratio of radiation received by (and emitted by) the two planets, is 1.93. Plugging in 1.93 and solving for TVenus, we learn that TVenus will be (1.93)1/4, or 1.18, times higher than TEarth. In all physical calculations involving temperature, we must always use the absolute temperature scale, measured in Kelvins (K). The Kelvin scale is defined so that zero corresponds to no energy and no thermal radiation. This is not true of the Celsius or Fahrenheit scales. If we use 68 °F as a characteristic temperature on Earth, TEarth is equal to 293 K. Multiplying 293 K by the factor 1.18, we get the answer that Venus would be 346 K, or roughly 163 °F. This is if the temperature difference between the planets was due only to solar distance. This calculation is actually confirmed by the temperatures of spacecraft when they fly toward the Sun and approach Venus. In other words, the temperature of Venus with an atmosphere the same as Earth’s would be 163 °F (346 K, 73 Celsius). This is too hot for comfort. If we terraformed Venus we’d have to reduce the inwards flux somehow, or it would be too hot. This could be done by increasing Venus’ albedo (note that Venus’ albedo is currently much higher than Earth, but if we assume an Earth-like atmosphere we should assume an Earth-like albedo, in the first approximation anyway). Another solution might be a sunshade in orbit or otherwise located between Venus and the Sun. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 3, 2016, 10:33pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/16 "2016-01-03T22:33:54Z")
> [@](#): > > (note that Venus’ albedo is currently much higher than Earth, but if we assume an Earth-like atmosphere we should assume an Earth-like albedo, in the first approximation anyway). I dunno; a planet’s worth of white paint sounds a lot easier than getting rid of 99% of an atmosphere of carbon dioxide and sulfuric acid. If you’re going to go to the effort of the latter, then you might as well do the former, too. Heck, maybe you can even turn some of the excess atmosphere into paint, somehow. Oh, and to nitpick your quote, while absolute temperature is required here, it’s not needed for _all_ temperature calculations. A lot of calculations depend only on temperature difference, in which case you can use any linear scale you like. ---
**Author:** ![sbunny8](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@sbunny8](https://boards.straightdope.com/u/sbunny8)\ **Post date:** [January 4, 2016, 12:31am UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/17 "2016-01-04T00:31:31Z")
IMHO, with or without the greenhouse effect, she’s still hot. [http://www.greek-mythology-pantheon.com/wp-content/uploads/Greek\_Gods\_and\_Goddesses/Aphrodite\_Venus\_Greek\_Goddess/Aphrodite\_Venus\_Greek\_Goddess\_Art\_07.jpg](http://www.greek-mythology-pantheon.com/wp-content/uploads/Greek_Gods_and_Goddesses/Aphrodite_Venus_Greek_Goddess/Aphrodite_Venus_Greek_Goddess_Art_07.jpg) ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [January 4, 2016, 3:16am UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/18 "2016-01-04T03:16:54Z")
> [@njtt](#): > > It is largely carbon dioxide, which is a much heavier gas than the nitrogen and oxygen that make up most of Earth’s atmosphere. > > If it wasn’t for plants eating up the CO2 and pooping out oxygen, our atmosphere would no be much different. Actually, what I’d heard was that it was the presence of liquid water on Earth that locked away vast amounts of CO2 as carbonate rock. Venus lost most of it’s hydrogen to photodisassociation, then any nitrogen and free oxygen, leaving mostly CO2 because it’s much heavier. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [January 4, 2016, 10:02pm UTC](https://boards.straightdope.com/t/how-hot-would-venus-be-without-the-greenhouse-effect/665497/19 "2016-01-04T22:02:06Z")
> [@Lumpy](#): > > Actually, what I’d heard was that it was the presence of liquid water on Earth that locked away vast amounts of CO2 as carbonate rock. Specifically, it was mainly calcium oxide disolved in the liquid water that combined with CO[sub]2[/sub] to form calcium carbonate. That wasn’t the only CO[sub]2[/sub] sink, but it was the largest. At high temperatures, calcium carbonate breaks down, releasing the carbon dioxide, so any that formed on Venus is no longer there. > [@](#): > > Venus lost most of it’s hydrogen to photodisassociation, then any nitrogen and free oxygen, leaving mostly CO2 because it’s much heavier. Actually Venus has as much or more nitrogen than Earth. Its percentage of Venus’ atmosphere is lower, but that’s because there’s so much more carbon dioxide. Any free oxygen (due to the photodissociation of water) would generally not have been lost, but rather have combined with unoxidized rocks.