<p>Firstly, Mars is farther away from the sun than Venus or Earth, so it gets less heat from the sun. Secondly, Venus &amp; Earth are volcanically active, whereas Mars is volcanically inert. Thirdly, the atmosphere on Mars is much thinner than those on Venus and Earth.</p>

<p>The density of the atmosphere on <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html" rel="noreferrer">Venus</a> is approximately $65\ \mathrm{kg/m}^3$, whereas, the density of <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html" rel="noreferrer">Earth's</a> atmosphere is $1.217\ \mathrm{kg/m}^3$ and the density of <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html" rel="noreferrer">Mars's</a> atmosphere is $0.02\ \mathrm{kg/m}^3$. Earth's atmosphere is 60 times denser than that of Mars; Venus's atmosphere is over 3000 times denser.</p>

<p>With such a thin atmosphere on Mars, there is little atmospheric mass to retain heat, despite the atmosphere being composed of 95.3 percent carbon dioxide.</p>

CC BY-SA 3.0
2017-03-08T08:01:35.673Z
So to rephrase a take home point: percentage is often a poor metric, because 98% of a sliver is still a sliver, and it's not enough to have a big impact.
JeopardyTempest
CC BY-SA 3.0
2017-03-08T08:05:34.220Z
Coincidentally, just in case you happen to know... any idea which of your three factors dominate the others Fred?  If Mars had 1 of the 3, which would warm it the most?  Its always nice to get a scale idea when possible on lists of synoptic factors.
JeopardyTempest
CC BY-SA 3.0
2017-03-08T15:20:10.827Z
iven if water is not mentioned in the question it do play a big role in combination whith co2 on the earths atmosphere .water on mars is too cold to stay liquid and end up in the atmosphere and venus is too hot for liquid water to form.
trond hansen
CC BY-SA 3.0
2017-03-09T10:25:20.887Z
I think you should mention that Venus is not confirmed to be active it is believed but it has not been confirmed.
Lucian09474
CC BY-SA 4.0
2018-07-26T16:03:23.357Z
Just to elaborate the first point, the mean distances are 0.723 AU, 1 AU and 1.524 AU for Venus, Earth, and Mars, respectively. Radiation is proportional to the square of the distance, so the radiation received by Venus is 1.524^2 / 0.723^2 ~= 4.44 times as much as the radiation received by Mars.
Victor Engel
CC BY-SA 3.0
2017-03-08T07:56:27.837Z
2018-01-06T14:22:16.903Z
2018-01-06T14:22:16.903Z
Fred
<p>In addition to what has been said by @Fred, I'd like to add that CO2 doesn't actually generate heat, it is just very good at trapping heat. Mars doesn't get as much heat as Earth, and it also doesn't have enough CO2 to effectively trap heat that has been received, as a result, it's much colder than Earth. </p>

CC BY-SA 3.0
2017-04-14T19:34:33.400Z
Effective temperature is not very useful. It bears no relation to the thing that is really of interest and that is the temperature of the very tiny thin region centered about the surface where the biological entities may live, fly or swim. Surface temperature is "everything" pretty well, surface is where you land the probes, explore, build your colony etc.
user7733
CC BY-SA 3.0
2017-03-08T19:29:20.293Z
And Venus gets lots more heat from the sun, and has lots more CO2 to trap that heat.  Which is why the surface is hot enough to melt lead, instead of the steamy tropical jungle imagined by 1930s SF writers - which it probably would be if it had an Earthlike atmosphere (and water, of course).
jamesqf
CC BY-SA 3.0
2017-03-09T17:35:28.563Z
@jamesqf I was going to post an answer to that effect, but when I did the math, it turns out that isn't exactly true. Venus' albedo is very high (0.7) due to its clouds, while Earth (0.3) and Mars (0.16) are much lower. Therefore, in the climate model sense, it receives less heat than Earth and only a bit more than mars. The [effective temperature](https://en.wikipedia.org/wiki/Effective_temperature) of Venus is 232K, while Earth is 254K and Mars is 207K.
kingledion
CC BY-SA 3.0
2017-03-09T23:45:55.557Z
@kingledion: But effective temperature and surface temperature are two quite diffenent things, no?  Perhaps I'll have a better answer after I work my way through "Principles of Planetary Climate", but this thread is likely to be a bit dated by then :-)
jamesqf
CC BY-SA 3.0
2017-03-08T13:48:30.293Z
2017-03-08T13:48:30.293Z
TonyC
<p>First Venus has a very thick carbon dioxide atmosphere that traps heat. Wile mars also has a carbon dioxide atmosphere but unlike Venus it is very thin and mars is much further from the sun and there for can't really trap much heat.</p>

CC BY-SA 4.0
2021-10-22T20:52:19.330Z
2021-10-22T20:52:19.330Z
Truman Bond
<p>CO2 does NOT control Earth's Climate, it plays a role, but so do other factors., in it's long geologic and shorter term histories. It played a role when CO2 was 10x that of present. Even so we had an Ice Age during the Ordivician (4,400 ppm). Jurassic cooling period (1,700 ppm)
The biggest influencer is the Sun. magnetic anomolies, sunspots, milankovitch cycles. Earth's orbit and axial tilt variation that permit More or less solar absorption.</p>
<p>For the last 800,000 years, Earth's ambient CO2 NEVER went up above 280 ppm average. In the last 10,000 years, we've had 20 major warming and cooling events and ambient co2 remained fairly constant.....</p>
<p><a href="https://i.sstatic.net/SHGgq.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/SHGgq.jpg" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2021-10-25T20:52:35.060Z
Downvoted. Doesn't answer question and misrepresents the current significance of CO2 to climate. CO2 is the single strongest cause of current climate CHANGE. It IS "controlling" the change to Earth's climate now more than any other factor, irrespective of other periods of climate change not being because of changes to CO2. The graph is very misleading - deliberately? One region only, not Global. Missing the full range of relevant data available that together does show the significance of anthropogenic emissions. And with the largest part of recent warming - post 1970s - missing.
Ken Fabian
CC BY-SA 4.0
2021-10-25T21:30:43.723Z
1 degree C in the span of 150 years is not a detriment. Nor is it indicative of widespread shift. The little ice age lowered average Temps 1.5 degrees with same ambient co2. Compare CET central England temperature which goes back to the 1650s to CO2 by year. Note Temp curve failed to obey the Co2 curve. 80% of all greenhouse gas emissions originated in the last 50 years. Tempsvdid not follow the same geometric rate..
LazyReader
CC BY-SA 4.0
2021-10-26T23:40:54.690Z
Your answer and comment are not consistent with current science based understanding of our climate system, it's history and current climate change.
Ken Fabian
CC BY-SA 4.0
2022-10-30T04:09:49.040Z
The little ice age also hade four massive volcanic eruptions, co2 can't warm by trapping heat from sunlight if you cut down the amount of sunlight.  we know what caused worming in the past and we know all of the factors except co2 are currently pushing cooling yet we are warming, co2 is literally overpowering the other factors. you mention several factors but fail to understand them. your graph is useless since it does not include co2.
John
CC BY-SA 4.0
2021-10-25T09:02:29.777Z
2021-10-25T09:02:29.777Z
LazyReader
<p>Hasn't anything to do with CO2. It's the atmospheric pressure. Venus receives very little sunlight but still very hot due to extreme pressure. Jupiter is extremely hot due the intense atmospheric pressure despite being much further from the sun. CO2 has very little effect trapping heat beyond 50ppm. The earth was in an ice age with 10 to 20 times the current CO2 levels</p>

CC BY-SA 3.0
2018-01-10T14:30:51.027Z
This is quite trivially incorrect - you would infer from that argument that if the sun was removed from the system, the planets would not freeze.  For instance, Titan has an atmospheric surface pressure 1.5 times that of Earth, but is cold enough for liquid methane lakes to form.  Jupiter is hot because it is still cooling down from it's formation.
Andrew Jon Dodds
CC BY-SA 4.0
2021-10-27T20:38:27.670Z
@Ron Your answer is not consistent with current science based understanding of our climate system, it's history and current climate change.
Ken Fabian
CC BY-SA 4.0
2022-10-30T04:26:46.920Z
if you are referring to the late Ordovician that glacial period came with a massive drop in co2. they were high before and after but not during.
John
CC BY-SA 3.0
2018-01-06T12:15:17.173Z
2018-01-06T12:15:17.173Z
Ron
<p>Earth's atmosphere is 0.038% carbon dioxide. Mars's atmosphere is 95.3% carbon dioxide. Venus's atmosphere is 96.5% carbon dioxide.</p>

<p>If Earth's climate is controlled by CO<sub>2</sub>, then why is Mars so cold in comparison to Venus? Mars is very cold (average about &ndash;60&deg;C) and Venus is very hot (+460&deg;C). </p>

CC BY-SA 3.0
2017-03-08T18:47:37.157Z
climate isn't controlled by CO2... it is just sensitive to it... just as it is sensitive to many other factors.
f.thorpe
CC BY-SA 4.0
2018-08-06T00:21:45.960Z
The important difference between Mars and Venus is obviously not CO2 or water, or distance from the Sun for that matter, but the atmospheric pressure.
You can easily determine the surface temperature if you know a few parameters like the molecular composition/weight and the pressure using the Boltzmann constant.
Surface temperature is on no planet determined by only greenhouse gasses.
priffe
CC BY-SA 4.0
2022-10-29T14:13:39.660Z
Pressure contributes to the greenhouse effect by broadening absorption lines, but it cannot in and of itself heat a planet's surface. Planets radiate away heat, so a planet heated (via the ideal gas law) by a one-time compression of their atmospheres would have cooled off by now. For the planet to keep heating because of a high-pressure atmosphere would make planet atmospheres a perpetual motion machine of the first kind, creating energy out of nowhere.
bpl1960
CC BY-SA 4.0
2022-10-29T18:29:52.027Z
Is this supposed to be a comment to Ron's answer?
JeopardyTempest
<climate-change><planetary-science><co2><mars>
Carbon dioxide on Mars, Venus and Earth
Lucian09474
# Carbon dioxide on Mars, Venus and Earth

(Asked by: username_0 on 2017-03-08)

Earth's atmosphere is 0.038% carbon dioxide. Mars's atmosphere is 95.3% carbon dioxide. Venus's atmosphere is 96.5% carbon dioxide.

If Earth's climate is controlled by CO2, then why is Mars so cold in comparison to Venus? Mars is very cold (average about –60°C) and Venus is very hot (+460°C).

**Tags:** climate-change, planetary-science, co2, mars

> **Comments:**
> **username_1**: climate isn't controlled by CO2... it is just sensitive to it... just as it is sensitive to many other factors.  
> **username_2**: The important difference between Mars and Venus is obviously not CO2 or water, or distance from the Sun for that matter, but the atmospheric pressure. You can easily determine the surface temperature if you know a few parameters like the molecular composition/weight and the pressure using the Boltzmann constant. Surface temperature is on no planet determined by only greenhouse gasses.  
> **username_3**: Pressure contributes to the greenhouse effect by broadening absorption lines, but it cannot in and of itself heat a planet's surface. Planets radiate away heat, so a planet heated (via the ideal gas law) by a one-time compression of their atmospheres would have cooled off by now. For the planet to keep heating because of a high-pressure atmosphere would make planet atmospheres a perpetual motion machine of the first kind, creating energy out of nowhere.  
> **username_4**: Is this supposed to be a comment to Ron's answer?  

---

## 5 answers

### Answer by username_5 on 2017-03-08. Score: 10

Firstly, Mars is farther away from the sun than Venus or Earth, so it gets less heat from the sun. Secondly, Venus & Earth are volcanically active, whereas Mars is volcanically inert. Thirdly, the atmosphere on Mars is much thinner than those on Venus and Earth.

The density of the atmosphere on [Venus](https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html) is approximately $65\ \mathrm{kg/m}^3$, whereas, the density of [Earth's](https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html) atmosphere is $1.217\ \mathrm{kg/m}^3$ and the density of [Mars's](https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html) atmosphere is $0.02\ \mathrm{kg/m}^3$. Earth's atmosphere is 60 times denser than that of Mars; Venus's atmosphere is over 3000 times denser.

With such a thin atmosphere on Mars, there is little atmospheric mass to retain heat, despite the atmosphere being composed of 95.3 percent carbon dioxide.

> **Comments:**
> **username_4**: So to rephrase a take home point: percentage is often a poor metric, because 98% of a sliver is still a sliver, and it's not enough to have a big impact.  
> **username_4**: Coincidentally, just in case you happen to know... any idea which of your three factors dominate the others username_5?  If Mars had 1 of the 3, which would warm it the most?  Its always nice to get a scale idea when possible on lists of synoptic factors.  
> **username_6**: iven if water is not mentioned in the question it do play a big role in combination whith co2 on the earths atmosphere .water on mars is too cold to stay liquid and end up in the atmosphere and venus is too hot for liquid water to form.  
> **username_0**: I think you should mention that Venus is not confirmed to be active it is believed but it has not been confirmed.  
> **username_7**: Just to elaborate the first point, the mean distances are 0.723 AU, 1 AU and 1.524 AU for Venus, Earth, and Mars, respectively. Radiation is proportional to the square of the distance, so the radiation received by Venus is 1.524^2 / 0.723^2 ~= 4.44 times as much as the radiation received by Mars.  

---

### Answer by username_8 on 2017-03-08. Score: 2

In addition to what has been said by @username_5, I'd like to add that CO2 doesn't actually generate heat, it is just very good at trapping heat. Mars doesn't get as much heat as Earth, and it also doesn't have enough CO2 to effectively trap heat that has been received, as a result, it's much colder than Earth.

> **Comments:**
> **username_10**: And Venus gets lots more heat from the sun, and has lots more CO2 to trap that heat.  Which is why the surface is hot enough to melt lead, instead of the steamy tropical jungle imagined by 1930s SF writers - which it probably would be if it had an Earthlike atmosphere (and water, of course).  
> **username_11**: @username_10 I was going to post an answer to that effect, but when I did the math, it turns out that isn't exactly true. Venus' albedo is very high (0.7) due to its clouds, while Earth (0.3) and Mars (0.16) are much lower. Therefore, in the climate model sense, it receives less heat than Earth and only a bit more than mars. The [effective temperature](https://en.wikipedia.org/wiki/Effective_temperature) of Venus is 232K, while Earth is 254K and Mars is 207K.  
> **username_10**: @username_11: But effective temperature and surface temperature are two quite diffenent things, no?  Perhaps I'll have a better answer after I work my way through "Principles of Planetary Climate", but this thread is likely to be a bit dated by then :-)  
> **username_9**: Effective temperature is not very useful. It bears no relation to the thing that is really of interest and that is the temperature of the very tiny thin region centered about the surface where the biological entities may live, fly or swim. Surface temperature is "everything" pretty well, surface is where you land the probes, explore, build your colony etc.  

---

### Answer by username_12 on 2021-10-22. Score: 1

First Venus has a very thick carbon dioxide atmosphere that traps heat. Wile mars also has a carbon dioxide atmosphere but unlike Venus it is very thin and mars is much further from the sun and there for can't really trap much heat.


---

### Answer by username_13 on 2021-10-25. Score: -2

CO2 does NOT control Earth's Climate, it plays a role, but so do other factors., in it's long geologic and shorter term histories. It played a role when CO2 was 10x that of present. Even so we had an Ice Age during the Ordivician (4,400 ppm). Jurassic cooling period (1,700 ppm)
The biggest influencer is the Sun. magnetic anomolies, sunspots, milankovitch cycles. Earth's orbit and axial tilt variation that permit More or less solar absorption.

For the last 800,000 years, Earth's ambient CO2 NEVER went up above 280 ppm average. In the last 10,000 years, we've had 20 major warming and cooling events and ambient co2 remained fairly constant.....

[![enter image description here](https://i.sstatic.net/SHGgq.jpg)](https://i.sstatic.net/SHGgq.jpg)

> **Comments:**
> **username_14**: Downvoted. Doesn't answer question and misrepresents the current significance of CO2 to climate. CO2 is the single strongest cause of current climate CHANGE. It IS "controlling" the change to Earth's climate now more than any other factor, irrespective of other periods of climate change not being because of changes to CO2. The graph is very misleading - deliberately? One region only, not Global. Missing the full range of relevant data available that together does show the significance of anthropogenic emissions. And with the largest part of recent warming - post 1970s - missing.  
> **username_13**: 1 degree C in the span of 150 years is not a detriment. Nor is it indicative of widespread shift. The little ice age lowered average Temps 1.5 degrees with same ambient co2. Compare CET central England temperature which goes back to the 1650s to CO2 by year. Note Temp curve failed to obey the Co2 curve. 80% of all greenhouse gas emissions originated in the last 50 years. Tempsvdid not follow the same geometric rate..  
> **username_14**: Your answer and comment are not consistent with current science based understanding of our climate system, it's history and current climate change.  
> **username_15**: The little ice age also hade four massive volcanic eruptions, co2 can't warm by trapping heat from sunlight if you cut down the amount of sunlight.  we know what caused worming in the past and we know all of the factors except co2 are currently pushing cooling yet we are warming, co2 is literally overpowering the other factors. you mention several factors but fail to understand them. your graph is useless since it does not include co2.  

---

### Answer by username_16 on 2018-01-06. Score: -4

Hasn't anything to do with CO2. It's the atmospheric pressure. Venus receives very little sunlight but still very hot due to extreme pressure. Jupiter is extremely hot due the intense atmospheric pressure despite being much further from the sun. CO2 has very little effect trapping heat beyond 50ppm. The earth was in an ice age with 10 to 20 times the current CO2 levels

> **Comments:**
> **username_17**: This is quite trivially incorrect - you would infer from that argument that if the sun was removed from the system, the planets would not freeze.  For instance, Titan has an atmospheric surface pressure 1.5 times that of Earth, but is cold enough for liquid methane lakes to form.  Jupiter is hot because it is still cooling down from it's formation.  
> **username_14**: @username_16 Your answer is not consistent with current science based understanding of our climate system, it's history and current climate change.  
> **username_15**: if you are referring to the late Ordovician that glacial period came with a massive drop in co2. they were high before and after but not during.  

---

