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According to IPCC:

Climate change can be a significant driver of desertification and land degradation and can affect food production, thereby, influencing food security.

Source: IPCC

My concern is if greenhouse gasses increase the temperature, there is more evaporation, so more clouds, so more rainfall.

Why does climate change generate desertification instead?

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    $\begingroup$ Higher temperatures lead to both more evaporation, higher dew points and changing weather patterns. More evaporation over land means less moisture in the ground, which facilitates desertification. Higher dew points lead to "later" formation of clouds. Changing weather patterns mean changing rainfall patterns, more flashfloods etc. So yes, the overall moisture in the atmosphere most likely increases, but the distribution and rainfall doesn't stay the same. $\endgroup$ – Erik Feb 18 at 8:28
  • $\begingroup$ The Sahara is pretty hot, and is a desert. So is much of Australia, and a number of (though not all) places with notable deserts. Yet if high temperatures increased rainfall, they should not. OTOH, some places with lots of rainfall - the Pacific Northwest, the British Isles - are generally fairly cool. $\endgroup$ – jamesqf Feb 18 at 18:38
  • $\begingroup$ @Erik that sounds like the beginnings of a solid answer. $\endgroup$ – John Feb 19 at 21:32
  • $\begingroup$ Thank you @John but currently I am not able to provide a really solid answer - hence the comment. $\endgroup$ – Erik Feb 20 at 12:33
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Most arid and semi-arid regions are normally far inland. Often those also have terrain features that don't allow for the moist air to reach, such as mountain ranges, etc.

So now if global temperatures increase, the evaporation in semi-arid regions increase as well, reducing the amount of water available for plants. At the same time moisture coming from the ocean still precipitates as rain before reaching those regions.

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    $\begingroup$ Not really true. Lots of arid areas are close to, if not right on, coasts. For instance Baja California, the Atacama desert, the Namib, most of the Arabian peninsula. Other arid areas, like California's Central Valley and the Great Basin, aren't all that far from the coast, it's just that there are mountain ranges in between. $\endgroup$ – jamesqf Feb 19 at 19:02
  • $\begingroup$ yeah desert placement has more to due with global air cells than how close they are to the coast. $\endgroup$ – John Feb 19 at 21:31

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