Global warming is predicted to induce desiccation in many world regions through increases in evaporative demand and altered precipitation patterns. Rangelands, where net primary production (NPP) is limited primarily by water, may be among the more susceptible ecosystems to climate change. While NPP tends to be low in most rangelands, they account for over 40% of Earth's terrestrial surface, and provide the majority of forage for the world's domestic livestock. Even small changes in NPP or shifts in dominant plant species are certain to have significant impacts on water and nutrient cycling, NPP and plant-animal interactions, all with important consequences for the societies which depend on rangelands. Our group has conducted two field experiments in which we have evaluated another important factor in climate change, the direct effects of rising CO2 on plant physiology, soil-plant water relations, and ecology of semi-arid rangelands of the western Great Plains. Results from our experiments indicate that water use efficiency (WUE) in semi-arid grasslands, such as occur in the eastern Colorado and Wyoming, increase significantly when ambient CO2 concentration are artificially raised to simulate future CO2-enriched environments. This effect is due to the sensitivity of plant stomates to CO2, which tend to close and conserve water at higher CO2 concentrations. In an on-going Prairie Heating and CO2 Enrichment Experiment underway near Cheyenne, WY, the higher WUE due to increasing CO2 from present-day 390 ppm to 600 ppm was sufficient to off-set the desiccation due to a warming treatment which elevated canopy temperature by 1.5 C in the daytime and 3.0 C at night. These are conditions that we will likely face in the second half of this century. We've also learned that plant species are affected differently by these climate change treatments, with both warm-season grasses and invasive forbs being favored by future environments. I will discuss the implications of these findings in regards to the susceptibility of rangelands to climate change, and briefly comment on how we can use that information in the development of adapted management practices.