If you're going to travel the world many times, learn to sail and favor trains. Or define "world" as smaller than the actual globe.

The benefits of travel are numerous. They were there before our understanding of global heating and pollution. Times have changed since sentiments like in this post.

We have to factor our new understanding into our models for a good life. Seeing as how billions of people before flying led happy lives, flying around the world four times isn't necessary.

(To clarify, Derek didn't say you have to fly around the world four times. He wrote it generally enough that you could interpret it several ways, but I expect many people will interpret him to mean fly around the world four times.)