Earth v Mars v Venus

[Lborobrewer]

Is the surface temperature of Mars what it should be given the thickness of its atmosphere, or is it higher than expected ?

The reason for asking this question is that proportionally Mars has approximately 15 times as much CO2 in its atmosphere as the Earth has in its ( partial pressure of CO2 on Mars is approx 570 Pa, on Earth it is 39 Pa). Therefore it would not be unreasonable to expect the surface temperature of Mars to be higher than expected allowing for it's greater distance from the sun, due to the greenhouse effect.
For comparison, Venus, with a runaway greenhouse effect, has a CO2 partial pressure approximately 20000 times higher than that of Earth, although of course it is nearer to the Sun and receives proportionally more heating from the Sun.

[beso]

All gases are greenhouse gasses to some extent so the much lower total pressure does make a difference. We also have water which is a strong greenhouse absorber. Think of how cold a clear night sky can be.

By the way if you can get hold of a non contact infrared thermometer, point it at the sky even during the day and you would assume it was broken. I think the reading I have seen are around minus 150 Celcius. While this is well outside the calibration of the instrument it does show that it is very cold just out there beyond the atmosphere.

Over the next billion years we actually need to move the earth further from the sun, right out to the orbit of Mars if we are to survive the sun's increase in brightness over this time.

[jake-the-peg]

As beso says there's a lot more to it than just carbon dioxide!

The fact that mars is that much further away fror a start but also we tend to forget that Mars is quite a lot smaller than Earth and Venus.

Mars was once geologically very active but it's thought that that ceased sooner than Earth and Venus probably because of it's smaller size.

It's also almost certain now that there was once liquid water on the surface so temperatures were higher then and the atmosphere thicker (We also forget that the CO2 atmosphere on Mars is very thin indeed about the same that you would find 35Km up on Earth)

So there's a lot going on here it's not just about the Greenhouse effect

[Lborobrewer]

There is a lot of press given to the fact that fossil fuels contain ancient Carbon, when it is burnt it produces extra CO2. What is overlooked is that there is also ancient Hydogen, which is also released as extra water. For Natural gas, the amount of ancient water released is twice as much as ancient carbon dioxide. As water vapour is a potent greenhouse gas why is it not included in climate change discussions?
If the atmosphere is warming then the quantity of water vapour it can contain is increased, which can lead to higher temperatures and hence more water vapour being held in the atmosphere, is this potentially a more dangerous positive feedback cycle?