That is exactly how the term is used in regard to the amount of water in the air on Earth in comparison to Mars. The statements is always made in regard to ANYWHERE on Earth. It is certainly true on average Mars is drier than Earth. It is also true Mars is on average colder than Earth. But there localized sites and times where Mars is warmer than some locations on Earth, just as there are times and locations where Mars has more water vapor in the air than some sites on Earth, or using the terminology that is commonly used by Mars scientists, Mars is "wetter" than some sites on Earth at certain times.
This terminology has been used to indicate how difficult it is to have liquid water on the surface of Mars. My point is IF that is used as the criterion, THEN it is no more difficult and in fact less difficult than in Antarctica during those periods of the south pole Winter.
- Bob Clark
Space/Science » in reply to A bit of an exaggeration
The common use of terminology.