The hottest desert in the world -- is a tough one. The highest recorded one day temperature was in Tripoli, Libya (surprisingly Tripoli normally has a fairly mild climate). Also this is old information -- the US ARMY Corps. of Engineers recently published a verified set of Climate extremes for the world, it is available from the Nation Data Service. Generally, the Arabian Desert is often acknowledged as one of the hottest, driest sand deserts on earth. However, Death Valley CA has an average high of over 45C (115F) in July-- making it very hot on average.

-- Can you guess where the driest desert in the world is? -- It is a very cold one!

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Are you ready to go for a camel ride in the hottest desert on earth? Check out this website for the answer to your question and some information about how it used to be a wet grassland (How could that be?)

http://www.earthsky.com/1997/es970814.html