The drivers of this are not yet well understood but differences in rate of warming between land and ocean, and land surface water availability may be factors. Saturation—the point at which water vapor condenses back into water or ice, often forming clouds—depends on the air temperature, and air temperature around the world is also rising. Over many land areas, it’s getting warmer faster than it is getting wetter, which means the air is less saturated (relative humidity goes down), even as specific humidity goes up.