Why does London refrain for so long from mentioning the dog?

I'm not sure what you mean; we're introduced to the dog rather early in the story.

The dog is introduced in the 6th paragraph, preceding paragraphs detail the setting, weather, and the "man." The sixth paragraph nis where the introductions end, and the story begins.

why doesn't London mention the dog earlier though? is it so that the reader has more of a solitude feeling? and feeling of cold?

I don't see the delay in the dog's introduction as London's attempt to promote solitude. I simply see the man's story as picking up in that paragraph, after the reader has been given much needed information about the setting and set up of the story.

That doesn't mean I'm right of course, I've just never seen this story as one of human "solitude."

Huh? I'm Flynn J. Nice to meet you.