OK now that I got other things out of the way.
Understudy you can not go about adding to or taking away from something to make it work. The articles mentioned were not talking about dry ice or anything frozen in/on the ground, they talked about what is in the atmosphere. CO2.
Actually the article you cited, says:The explanation is in the dirt.
Glistening Martian dust lying on the ground reflects the Sun's light -- and its heat -- back into space, a phenomenon called albedo.
The article mentions nothing about CO2 levels on Mars. They do mention CO2 levels on Earth.
Now it either holds in heat or it doesn't. If it holds in the heat then the more you have the more heat you hold in. Can't be saying that a blanket will keep you warm on Earth but freeze you to death on Mars.
The top temprature on Mars 41F/5C but the colder tempratures are under 100F/-73C. I would think a blanket might not be adaquete. You mention a blanket keeps you warm or it doesn't. Sure if it is dry. And so is the surrounding enviroment. If the blanket is wet and temprature of the wet blanket is 85F/29.4C you will get hypothermia. The unfortunate fact is that when dealing with things like global warming and planetary atmospheres it is never as simple as we would like it to be. It is nice to be able to make simple comparisions but they don't always reflect the true nature. My salt analogy and your blanket analogy are like that.
Here is the thing, you expect things that work on earth to work the same way on mars. They don't This is the argument the people who feel the moon landings were faked bring up. CO2 alone does not hold in heat on the martian atmosphere. The martian atmosphere is very thin. This has a dramatic effect on how gases , vapors, and heat are trapped.
Nice Article. I will take my correction on that no problem. I still have some old viking lander articles I was looking at for that.
There is a more up to date NG article that discusses some of the dry ice issues. However the article you pointed out do state that the ice caps do contain frozen H2O.http://news.nationalgeographic.com/news/2005/12/1219_051219_mars_ice.html
However there is still science going on:http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=885&mode=thread&order=0&thold=0