Is there life on Mars?

I doubt it, but what I do know is that it has an atmosphere:

Despite the high concentration of CO2 in the Martian atmosphere [95%], the greenhouse effect is relatively weak on Mars (about 5°C) because of the low concentration of water vapour and low atmospheric pressure. While water vapour in Earth's atmosphere has the largest contribution to greenhouse effect on modern Earth, it is present in only very low concentration in the Martian atmosphere.

So the CO2 makes little difference then? It's the water vapour all of a sudden? (Venus also has hardly any water vapour and is 95% CO2).

What makes the big difference is the low atmospheric pressure, but they only mention that in passing. On the surface of Mars this is only 0.61% of sea level atmospheric pressure on Earth (and on the surface of Venus it is 92 times as much).

The effective temperature of Mars, i.e. its surface temperature if it had no atmosphere, is 210K. It's actual average surface temperature is 215K. To get the Barometric Formula to balance and give you an average temperature of 210K for the whole atmosphere*, you have to put in a surface temperatures between 215 and 218K.

This is not far off the official figure and gives you a lapse rate of a bit less than -1K/km altitude. NASA say it is almost exactly -1K/km. And they've been there and measured it. Interestingly, the altitude/temperature chart in the Wiki article (first link) also shows a lapse rate of about -1K/km, even though the article itself says actual -2.5K/km and predicted -4.3K/km,

So the formula comes through for us yet again; all that matters is that a mole of CO2 has an atomic mass of 44, about one-and-a-half times the mass of a mole of the Earth's atmosphere (mix of N2 and O2 = 29). You don't need to know anything else about the gases' properties.

As an approximation, density and pressure are proportional, so Mars has about fourteen times as many CO2 molecules per unit volume as Earth does. Earth = 420 ppm; Mars = 1,000,000 x 0.61% x 95% = 5,800.

So this next bit is a real cop-out:

Moreover, under low atmospheric pressure, greenhouse gases cannot absorb infrared radiation effectively because the pressure-broadening effect is weak.

CO2 molecules are a lot closer to each other on Mars than on Earth!

* Earth's effective temperature is given as 255K, which is very close to the average temperature of the atmosphere, depending on how it is calculated. So let's assume that the the average temperature of a planet's atmosphere is equal to its effective temperature. The charts tell us that the surface temperature is higher than the average and the temperature at the top of the stratosphere is lower than the average.