The Contrail OBservations And Lifecycle Tracking (COBALT) project - Observations and initial results

Aircraft are a growing proportion of the human forcing of the climate system, with the majority of their warming effect coming from their impact on clouds. Accurate modelling of these impacts is essential for guiding climate mitigation choices, but there are limited observations available to evaluate the capability of these models.  Matching aircraft tracks to data from a cloud radar, an array of ground-based cameras and satellite observations, the Contrail OBservations And Lifecycle Tracking (COBALT) project is constructing an evaluation dataset for models of contrails and aircraft impacts on existing cloud.                                             

                                                                                                               

Here we present the design of the COBALT observations, along with initial results for data collected over the southern UK in late 2024/early 2025. Matching the ground-based observations to satellite data, we build up a composite picture of contrail evolution behind specific aircraft from the first minutes of the contrail lifecycle to several hours after formation. This provides a unique dataset for contrail model evaluation and will help guide future observational studies to further assess the non-CO₂ impact of aircraft on climate.