The following link is a nice article explaining how to use the screen scrollback buffer:
$HOME/.screenrc set: defscrollback 5000
Finally, if you want to change the number of lines of scrollback for a single window, using the “scrollback” command. Hit C-a (Ctrl-A) : to go to the Screen command line and type scrollback num, where num is the number of scrollback lines.
To enter scrollback hit C-a [. A status line will indicate that you’ve entered copy mode. To exit scrollback mode, hit the escape button.
Very useful article.