A scoping review of celebrity endorsement in environmental campaigns and evidence for its effectiveness by Olmedo, A, Milner-Gulland, EJ, Challender, DWS, Cugnière, L, Dao, HTT, Ngyuen, LB, Nuno, A, Potier, E, Ribadeneira, M, Thomas-Walters, L, Wan, AKY, Wang, Y, Veríssimo, D