World Population Day will mark a global crisis – one that is best tackled by more access to birth control, particularly in Africa

President Magufuli pulled off an intriguing feat last year when, in a single speech, he managed to affront just about every liberal cause on the planet. The Tanzanian leader told a public rally not to listen to advice from foreigners on contraception because it had “sinister motives”. For good measure, he accused women who use birth control of being “lazy” – it was their duty to have large numbers of children.

By any standards, these were outrageous remarks – and worrying ones, for they indicate there has been a deep and potentially catastrophic failure by the west in promoting a measure on which the future health of our planet depends: limiting numbers of our species. Until this basic task is achieved, virtually every measure we take to tackle global heating will be negated by the energy demands of the extra billions we have added to global populations, say campaigners.