Duh. Deserts hot. Smaller desert means less heat? Less heat means cooler climate?
Deserts are cold at night.......................
Yes a desert is hot, during the day. At night, it gets much colder than a non-desert area would. The average tends to be the same for a desert and non-desert given the same environmental locale.
Had these 'climate scientists' been around in medieval times they would have proclaimed that the sun would totally disappear forever based on it appearing shorter amounts of time near the end of the year (if they were living in about the same latitude as most of us are).
Any medieval scientists living near the Arctic Circle would predict that the Sun would soon dominate the sky forever, causing all the glaciers to melt and the oceans to rise hundreds of feet.
Speaking of oceans rising, the major ocean levels have not changed in thousands (or even hundreds of thousands) of years. It is the land which moves up and down.