CORRECTION
"...we find that air-travel for the 8 million visitors that year (average round trip of 12,473 km) produced 22.5 million metric tons of CO2-eq."

[I was unable to make edits corrections because for a lengthy comment, your web page design shows the comment in the edit box, but the "save" button is cut off and the page won't scroll. I'm using Firefox mobile on Android. Also, if I'm not careful about scrolling while reading or commenting, the screen gets frozen, shows a partial left side bar, and has to be reloaded.  Very annoying. ]