A new European mission, the Far-infrared Outgoing Radiation Understanding and Monitoring mission, or FORUM, will add a crucial measurement to help our understanding of Earth’s changing climate. Measurements from the new spacecraft will improve confidence in the accuracy of climate change assessments that form the basis for future policy decisions. FORUM will record far-infrared radiation emitted from Earth to space – extending beyond the parts of the infrared spectrum currently being measured. The measurements will help the study of Earth’s radiation budget – the balance between the incoming radiation mostly from the Sun at short wavelengths, and outgoing radiation, which is a combination of reflected radiation from the Sun and radiation emitted by the Earth system, much of it a longer wavelengths. FORUM is ESA’s ninth Earth Explorer mission.