Analysis of observed data reveals upward trends in plant-available summer soil moisture content for agricultural regions of Russia, Ukraine, and Mongolia at the same time as these regions have warmed. These observed trends are evaluated using long-term equilibrium and transient runs of the GFDL coupled oceanic and atmospheric general circulation model. While observations are the opposite of what might be expected as the result of equilibrium doubled CO2 experiments, they agree with the latest transient runs, which show that summer soil moisture should increase during the 20th century. In the next century, as evapotranspiration increases faster than precipitation, summer drying is predicted to occur. We determine when this non-linear response is to be expected and, considering the natural variability of soil moisture, when we will be able to use this climate variation as fingerprint of global warming