Couples who have more than two children are being 'irresponsible' by creating an unbearable burden on the environment, the government's Sustainable Development adviser has warned. The adviser says that curbing population growth through contraception must be at the heart of policies to fight global warming. Political leaders and 'green' campaigners should stop dodging the issue of environmental harm caused by an expanding population. Each baby born in the UK will, during his or her lifetime, burn carbon roughly equivalent to 2½ acres of woodland – an area the size of Trafalgar Square. The UK population, now 62 million, will exceed 70 million by 2028. On average, women born outside the UK have 2.5 children compared with 1.7 for those born in the UK. The global population of 7 billion is expected to rise to 9.2 billion by 2050. Governments of both developed and developing nations must act to limit family size if they are serious about reducing energy consumption.