Question

What made the climate of northern Africa change from tropical to grasslands, and then to desert?

Answer 1

Ice Ages.

Step-by-step explanation:

This dramatic weather changes is due to Ice Age, because during this period On Earth's surface was continental and polar ice sheets, alpine glaciers and this tended to shift with greenhouse periods.

So, after glacial period became the Holocene period, which is today's geological epoch.

Answer 2

The cause of this would be the tilt of the Earths axis.