So 5-6 million years ago, the strait of Gibraltar closed due to plate tectonics. Because of this the Mediterranean dried up (maybe leaving a couple small very salty lakes). This would have made Europe much drier, maybe even gave it a desert. This event is expected to happen again in the future.
So 5-10 thousand years ago, a combination of Milankovitch cycles stuff, topography, and albedo-by-vegetation feedback loops caused the Sahara desert to become a vast grassland. This event will also happen in the future, as the Greening and Deserting of the Sahara happens in a 41000 year cycle.
I am thinking of a world in the future where both of these events happen at the same time. However, these conditions are obviously contradictory. The Salinity Crisis happened mainly because the strait of Gibraltar closed, which prevented the Mediterranean from being able to receive water from the Atlantic (The Mediterranean evaporates much of its water, and Atlantic Ocean is it's main source of water.) Green Sahara happens due to Axial Changes over time, the Northern Hemisphere would receive more energy, which means more evaporation, which means more rainfall, which is the seeds for plants to grow. Plants draw out groundwater and most of it is evaporated off leaves, more water. The plants increase the albedo which means more energy which means more rainfall and- oop we have got a feedback loop.
As you can see, with a grassy Sahara that receives rainfall (and the seasonal monsoon), it seems a little weird that there could be a very dry Mediterranean Basin next door. So what I want to ask is, would it be plausible for a Green Sahara to co-exist right next to a dried up Mediterranean Sea (with the exception of some small lakes of brine)?
- There must be a Green Sahara in the Sahara (with its rainfall and its monsoon)
- There must be a desiccated (dried up) Mediterranean Basin (going through something similar to the Messinian Salinty Crisis), with the exception of some small very very salty lakes collected at the deepest parts.
- To be more specific about the Mediterranean Basin, it should not be receiving much rainfall, however the Sahara must receive a nice dose of it, for it to be grassland. The Mediterranean sea can permit a small amount of it, as evaporation will take care of it