Quote:
Originally Posted by Ladogaboy
I agree, but especially in the case of the Sahara, animals could not be responsible for the reduction in rainfall over the last 10,000 years.
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Sure they could, if you understand what's going on. Simplified a bit (and you're perfectly welcome to do background research to fill in the details), a grassland traps moisture and is cooler than bare dirt, which captures more heat from the sun than plants - something you can experience for yourself if you've ever spent time in the country in the summer, and noticed that it's cooler when you're driving by pastures than plowed fields. All else being equal, you will get more rain from a given air mass when it's cooler.
So when a humid air mass swept across a grassland-covered Sahara, it'd drop X amount of rain (or dew etc). Pass that same air mass over the Sahara after grazing has denuded it of vegetation, and it'll drop only a fraction of the amount of rain, which isn't enough to allow a vegetation cover to re-establish itself.