The reliable detection of carbon dioxide (CO2) emissions is a key step towards the ability to mitigate CO2 levels in the atmosphere. At present, many CO2 sensors exist, but they all require on the order of watts of power, therefore, they are not suitable for long term unattended operation. In this paper, we present a new design for a microfabricated CO2 sensor that operates at room temperature with very low power input. The device uses the selective adsorption of CO2 in a room temperature ionic liquid (RTIL) followed by an electrochemical reaction at a gold electrode to detect the presence of CO2. We find that the device is able to measure normal atmospheric levels of CO2 with high reliability using less than 10 μW of power. This advance will enable a new class of portable CO2 sensors to be constructed.