Too many people living in urban sprawl. They are sucking on the groundwater too hard.
Ding Ding Ding, we have a winner!!
Back in college way back in the 1970's I took a geology course that documented land subsidence from groundwater withdrawal. Not only in Arizona, but in the south San Francisco bay area, Houston area and in sea coast regions of North Carolina. This was way before anyone thought of global warming due to man. There may be other reasons (e.g. plate tectonics), but the global warming hoax is not one of them.