In this story humans are not the environmental bad guys it would seem. The preaching bit takes a back seat as they are exonerated of blame. Indeed, they managed to hold back the onslaught of desertification in the Sahara (and presumably also in Arabia) even though we are talking about cattle herding pastoralists. Does this mean that the farting of cows in the proto desert environment was not as awfully bad as has been made out in temperate parts of the world? At https://phys.org/print457605723.html … we have a study into how humans impacted the global desertification of the Sahara. We are told that up to 8000 years ago the Sahara was green, a vibrant ecosystem with lots of plants, animals, and water resources (including lakes and rivers). It was much wetter – and it is presumed the monsoon track differed back then and subsequent orbital changes (the Milankovitch theory) has caused the Sahara to dry up as the monsoon track retreated southwards – gradually, over several thousand years. In this study we are told the greening came to an end at a specific point in time – around 6000BC. Thereafter, the environment of the Sahara went into terminal decline, we are told – with the caveat the desert did not arise instantly but its water resources dwindled substantially. However, pastoralism had appeared in the region a thousand years prior to the decline. Naturally, they were targeted as easy pickings and labelled as the bad guys, over grazing and that sort of thing. In the new study they are exonerated as already noted – but why? The authors used modelling that included a declining monsoon level of rainfall, a lesser amount of solar energy (as in earth's subtle orbital changes as it rotates around the Sun), and lastly, the assumption there was a lot less co2 in the atmosphere back then (even though there were plenty of cows ruminating and chewing the cud). The authors say the numbers don't add up – the desertification should have begun somewhat earlier. It didn't. The cattle herders seem to have adapted to a less lush environment and took care by not over graze the declining pockets of grassland. Or that is their conclusion. A noble one I might add as blame by association tends to stick. The cattle herders may therefore have had nothing to do with the switch – but what else might that mean? It may imply there was a massive change in rainfall levels at a specific point in time – 6000BC, which coincides with big changes elsewhere around the globe. For example, in South America there is evidence of a drop in sea levels but in Indonesia precisely the opposite – a massive rise in sea levels which flooded Sunda Land and created the many islands that now exist in the region, In additon, the North Sea basin flooded with evidence of a tsunami wave along the NE shores of Britain, and the Channel flooded as evidenced from the Boldnor Cliff marine archaeology research team findings of a few years ago. Also, at the same point in time North America entered what is known as the Mid Holocene Climatic Optimum, with evidence of an expansion northwards of the tree line (and an expansion upwards in mountainous zones). It would seem that big changes were afoot around 6000BC – and not just in the Sahara. Of course, the full weight of desertification was a gradual process as water resources did not disappear over night. They simply did not replenish to the degree required – and rivers and streams gradually became dry wadis (not just in the Sahara but in Arabia as well). In the subsequent few thousand years desertification waxed and waned as blips in the climate caused temporary very dry episodes – stranded in longer periods of stability. The drying out of the desert led to migration into the Nile Valley (where permanent communities were established). This ostensibly occurred somewhat later than 6000BC so we may assume it was possible to live in the Sahara up to at least 4000BC (and some communities remained in the desert right into the modern era). However, ancient water resources were exploited in the Hoggar region and other pastoral tribes moved south towards the Sahel. If the models do not include catastrophism as a factor worth keying in they will not produce a result that factors in catastrophic change (sudden global change in climate and sea levels that seem to reflect a changing geoid and perhaps a relocation of the equatorial bulge).