Competing Interests: Competing interests: We have read and understood BMJ policy on declaration of interests and declare HF is a member of advisory boards (or equivalent committees) for the Planetary Health Alliance, the Harvard Center for Climate, Health, and the Global Environment, the Medical Society Consortium on Climate Change and Health, the Global Consortium on Climate and Health Education, the Yale Center on Climate Change and Health, and the European Centre for Environment & Human Health at the University of Exeter—all unfunded positions. He is employed by Trust for Public Land, an environmental NGO which has action on climate change as one of its strategic priorities. JD is on the executive of the UK Health Alliance for Climate Change.