This paper describes an optical fibre based system suitable for monitoring the presence of carbon dioxide, "the Greenhouse gas", in the exhaust system of a motorvehicle. Conventional automotive pollution sensors fail to meet monitoring requirements as specified by the European Commission for various reasons. The design of this sensor using low cost and compact mid-infrared components, which make it suitable for insertion into a vehicle, is discussed. The response of the sensor to carbon dioxide supplied from a cylinder in the laboratory is presented. An initial measurement of the carbon dioxide concentration in the exhaust system of a commercial diesel engine using the optical fibre sensor is also presented. (C) 2006 Elsevier B.V. All rights reserved.