Global carbon emissions continue to increase, resulting in rising temperatures that pose a direct threat to human health.1 Health care contributes around 5% of all global carbon emissions,1 and many health systems have committed to developing sustainable approaches to health care.2 Cancer treatment, including surgery, radiotherapy, and systemic therapies, often takes place in specialist centres over many months or years and so is likely to have a considerable carbon footprint, although there have been few studies assessing cancer care carbon emissions to date.