Gatwick’s second runway is yet another example of the tragedy of the commons (Gatwick given green light for £2.2bn second runway plan, 21 September). While all nations benefit from a healthy climate, each also benefits from actions which damage the climate. Only international cooperation – including a binding agreement to phase out fossil fuel production – can prevent this tragedy. Neil BlackshawAlnwick, NorthumberlandIs Trump hoping to win a Nobel peace prize or a Nobel prize in physiology or medicine? Felix BellabyBuxton, DerbyshireAn increasing number of charities are severing ties with Sarah Ferguson.