I believe these numbers well accepted, not at all controversial. The conclusions some people draw are.
From
http://www.agu.org/sci_soc/mockler.html
" the average water molecule spends about 9 days in the air before precipitating back to the surface."
For a poission process half-life and average are identical. Since a water vapor molecule doesn't retain any information about how long it's been since it evaporated, it must be a possion process. They said "average" because it's more familiar to most people. The point's the same either way.
From
http://www.climate.org/topics/climate/index.shtml
"the half-life of carbon dioxide is on the order of a century."
They said "half-life" either because they weren't thinking about their audience, or they were and thought "half-life" sounded more scientific. (I wasn't thinking about my audience.)