Sorry posting has been light, but I am working on starting a new series of videos. At some point I want to update the old ones, but right now I want to experiment with some new approaches — the old ones are pretty good, but are basically just powerpoint slides with some narration. If you have not seen the previous videos, you may find them as follows:
- The 6-part, one hour version is here
- The 10-minute version, which is probably the best balance of time vs. material covered, is here.
- The short 3-minute version I created for a contest (I won 2nd place) is here.
Combined, they have over 40,000 views.
I just did a little research after watching Earth: A Biography, with host Ian Stewart. I blogged about it at: http://ragnard.wordpress.com/wp-admin/post-new.php?posted=179
The bottom line is that Stewart claims the reason why Mars is so much colder than Earth is because it doesn’t have as much CO2 in its atmosphere. Unless I am making a big mistake, Mars has 15 times as much CO2 as Earth!
I thought I would post here to see if anyone could confirm my conclusion or show me my error.
Thanks in advance!
Ragnar,
It’s a little bit less than 15, I think, but your general conclusion is correct. You can’t assume surface pressure is proportional to atmospheric mass unless the gravity is the same.
The reason for the different temperature is a combination of it being further away and the atmosphere in total being very thin and dry. Without atmosphere, the difference in solar radiation would keep Earth at an average of 255K and Mars at an average of 216K. Their respective atmospheres warm Earth by about 33K, and Mars by about 11K. (But that’s all fudging certain complications a bit – regard this as a “back-of-an-envelope” calculation.)
Note that you can’t deduce too much directly from there being n times more CO2, whatever n might be, because the response is non-linear, and the physics also depends on the gravity and the rate of change of temperature with altitude, which are different between Earth and Mars. And in any case, most of the effect on Earth is because of water vapour, not CO2.
Thanks!
I believe you misspeak in your 10 minutes video. You say that a paper by McIntrye and McKitrick shows that half of the warming in the surface record is data error, not temperature. I believe that you are referring to a study by McKitrick and Pat Michaels: McKitrick, Ross and Patrick J. Michaels (2004). “Are Temperature Trends Affected by Economic Activity? Reply to Benestad (2004)” Climate Research 27(2) pp. 175-176
or
McKitrick, Ross R. and Patrick J. Michaels. (2007) Quantifying the influence of anthropogenic surface processes and inhomogeneities on gridded surface climate data. Journal of Geophysical Research-Atmospheres, in press.