Some people have suggested that we might be able to carry out planetwide enginnering of Mars that would cause its cliamte to warm and its atmosphere to thincken. This type of planet engineering is called terraforming, because its objuective is to make a planet more Earth-like and therefore easier for humans to live on. Discuss possible ways to terraform Mars, at leat in principle. Do any of these ideas seem practical? Does it seem like a good idea? Defend your opinions.