What percent of the worlds land surface is Desert?

This website lumps both sand and ice together.....and therefore between the two the earth is 33% desert.

Since the definition of desert I learned was a land area with less that 10" of precipitation a year, both polar regions are deserts. This definition makes Antarcticia the largerstr desert in the world, with 5.5 mil sq. mi. to the Sahahra's 3.5 mil.