In this post, I comment on entering copy mode in GNU screen in order to scroll back with the keyboard. But what if you just want to use the scroll wheel? I think what you're looking for is this line in your configuration file, ~/.screenrc:
# scrolling: termcapinfo xterm ti@:te@
I also found this cryptic code in my configuration file; I can't tell if it's relevant or not:
# Scroll up bindkey -d "^[[5S" eval copy "stuff 5\025" bindkey -m "^[[5S" stuff 5\025 # Scroll down bindkey -d "^[[5T" eval copy "stuff 5\004" bindkey -m "^[[5T" stuff 5\004 # Scroll up more bindkey -d "^[[25S" eval copy "stuff \025" bindkey -m "^[[25S" stuff \025 # Scroll down more bindkey -d "^[[25T" eval copy "stuff \004" bindkey -m "^[[25T" stuff \004
Happy screening!
