Al Gore being President would not have stopped 9/11... that was a ball set in motion long before the 2000 election.
The response to 9/11 might have been different since the Clinton / Gore administration had tended to deal with international terror attacks on the US as criminal matters rather than acts of war... but up until then none of the terror attacks had been anywhere near as successful at 9/11, so it is entirely possible that Gore would have had a similar response as Bush in Afghanistan. And the Patriot Act and Homeland Security came from Congress, which would have been the same makeup no matter who the President was.
What would have been different is we very likely would not have gone to war with Iraq, and we possibly could have ended up breaking ties with Saudi Arabia, if not going to war with them, over 9/11. The loss of Saudi Arabia as an 'ally' would have been a huge benefit for green infrastructure in the US.