[hinckley buzzard]

ancient Egypt did not have much in terms of fuel - no extensive forests.

There were extensive forests upstream on the Nile, easy to fell and float downstream; not to mention those cedars in nearby Lebanon.

[GSlob]

To burn enough lime for a large pyramid, one would need A LOT of wood. An 8 megaton pyramid - say, 2000000 ton of lime. 20 years time frame. 100000 tons of lime a year, 300 tons of lime a day, something like 1000 tons of wood per day. Egyptian expeditions to upper Nile were never large enough to pull out this kind of logging. And Egyptians in Lebanon date to much later times.

[Jedi Master Pikachu]

Plus, depending on how old the pyramids actually are, Egypt was very lush when first settled, desertification happening later (Creationist, in case you're wondering). The same with Sumer. Why would the two most powerful civilizations settle what today is (in terms of climate) relatively cruddy land?

P.S. During the Ice Age.