Increase buffer size while running screen

Do Ctrl + a : then enter scrollback 1234 sets your buffer to 1234 lines. You enter scrollback mode ("copy mode") with Ctrl + a Esc, then move in vi-style, leave copy mode with another Esc

I actually figured this out after looking through the man page. Setting the screen buffer inside .screenrc does work, but you can change it inside your screen session.

Ctrl-a + : and typing

scrollback 1000

gives you a 1000 line buffer.

You can also set the default number of scrollback lines in .screenrc by using

defscrollback 1000

Then entering copy mode will let you scroll around.

You actually do have something of a buffer, but it's invisible to most terminal emulators (which is why e. g. scroll bars don't appear to work). One way to get at it is to enter copy mode (Ctrl-A,[ followed by arrow keys, PgUp, et cetera). The size of this buffer can be configured in .screenrc. You you an change its allocation inside your screen session:

Ctrl-a + : and typing

scrollback 1000

gives you a 1000 line buffer.