too much carbon dioxide, which plants need for energy, actually can inhibit a plant's ability to assimilate nitrates — nitrogen-based nutrients pulled from the soil that plants use to make enzymes and other essential proteins.

The data has implications for the region's future climate as well. As Cole explains, it is well documented that, as the climate warms, storms in the southwestern United States tend to move northward toward the pole. The record clearly shows  that "when the climate gets warmer, the U.S. Southwest tends to get drier."