How to scroll up and look at data in GNU screen

There's a 'copy mode' in screen, activated by pressing, Ctrl + A, followed by [. This gives you a cursor that you can use to scroll backwards.

Add the following to your ~/.screenrc:

termcapinfo xterm ti@:te@
termcapinfo xterm-color ti@:te@

This will let you use the Terminal.app scrollbar instead of relying on screen's scrollback buffer.

The correct way is to use the copy mode, as Babu pointed out.

You could speed things up a bit by automatically entering into copy mode when you press your favourite scroll keys.

For example, using PgUp and PgDown:

# easier scroll
bindkey "^[[5~" eval 'copy' 'stuff ^b'  # PgUp   | Enter copy/scrollback mode and page up
bindkey "^[[6~" eval 'copy' 'stuff ^f'  # PgDown | Enter copy/scrollback mode and page down