Of the water on Earth, a small percentage was locked up in glaciers. Although all that ice (and whatever caused it), certainly changed the climate.
Its curious as to what caused the Holocene Wet Phase(from about 7500–7000 BC to about 3500–3000 BC), that turned the Sahara green. And just as curious as to what ended it.
Most likely camels driving SUVs.
I think I remember seeing on a documentary that during some of the dinasaur ages, the Sahara was a shallow sea.