I've had a theory about global warming. Basically if most of the earths water is locked up in the poles, this would cause arid regions to form. Releasing the water in the poles would have the opposite effect, causing more rainfall than normal since a greater surface area of the earth would be covered in water, likely swamp like forests.
If we look back at the start of the Carboniferous period, the earth was fairly warm, taken from
this Berkeley publication.The beginning of the Carboniferous generally had a more uniform, tropical, and humid climate than exists today. Seasons if any were indistinct. These observations are based on comparisons between fossil and modern-day plant morphology. The Carboniferous plants resemble those that live in tropical and mildly temperate areas today. Many of them lack growth rings, which suggests a uniform climate. This uniformity in climate may have been the result of the large expanse of ocean that covered the entire surface of the globe, except for a localized section where Pangea, the massive supercontinent that existed during the late Paleozoic and early Triassic, was coming together.
What we do know of these arid regions today is they were once covered with water. The main difference though is as humans, we're the only species smart enough to do things like build storm walls, reservoirs, and flood control measures. It would be interesting if global warming took us to the start of the Carboniferous, where the majority of the planet was warm, humid, and frequently rainy.