On 24 September 2019, a new ATSlab paper on carbon leakage in aviation policy was published in Climate Policy. This paper, based on work the authors carried out for the Department for Transport, shows that carbon leakage (i.e., the impact on carbon emissions outside an area where a carbon-reduction policy is applied compared to the impact on emissions inside the policy area) can be very large for aviation policies applied at the single-country level, and depends strongly on the type of policy and the scope the policy is evaluated on. This arises naturally from the global, interconnected nature of aviation systems.