Convective available potential energy (CAPE), a metric associated with severe weather, is expected to increase with warming, but we have lacked a framework that describes its changes in the populated midlatitudes. In the tropics, theory suggests mean CAPE should rise following the Clausius-Clapeyron (C-C) relationship at ~6%/K. In the heterogeneous midlatitudes, where the mean change is less relevant, we show that CAPE changes are larger and can be well-described by a simple framework based on moist static energy (MSE) surplus, which is robust across climate states. This effect is highly general and holds across both high-resolution nudged regional simulations and free-running global climate models. The simplicity of this framework means that complex distributional changes in future CAPE can be well-captured by a simple scaling of present-day data using only three parameters.