Do I add to or subtract from the argument?

Perhaps I owe an apology to a girl I knew in my undergrad years. She rather naively mused that if the Sahara Desert were planted with enough trees, the entire desert might revert to jungle. I scoffed at the notion, telling her that she was confusing cause and effect, but I now wonder if, maybe, just maybe, she wasn't entirely wrong, for we now know that a large rainforest alters the regional climate in its area.