"No _____er" or "No more _______" or both?
I've come across this construction "He is no more (adjective) than I am" more than once, and there are at least two forums on the Internet where the subject is discussed. Several explanations have been offered but there seems to be no consensus. Some say they mean the same while others find a semantic difference.
My question is: are they both grammatically correct? Do they mean exactly the same? Likewise, would it be grammatical to say "It's no more cold in Greenland than in Alaska", or "She is no more pretty than you are."
EDIT - From the comments and one answer I've got so far, I feel compelled to explain: I'm perfecly aware of how we form the comparative and superlative degrees of adjectives. What I'm asking here is whether some colloquialisms are acceptable, such as "A more silly comment I cannot imagine" to emphasize the idea attached to the positive degree, or "a more healthy-looking baby", or if there is any subtlety in "he is no more young than I am" as compared to "no younger".