In the early days of his first term, US president Barack Obama gave a speech in Prague in which he called for a world without nuclear weapons. His argument was based on a risk assessment:

In a strange turn of history, the threat of global nuclear war has gone down, but the risk of nuclear attack has gone up....

Most life in the sea ultimately depends on photosynthetic plankton. Also known as microalgae, these tiny or microscopic organisms live near the surface and take their energy from the sun and pass it on through the marine food chain.

But these plankton have a big...

Although things in Greece appear to have stabilised slightly after a fortnight of dramatic uncertainty, the heightened speculation on the future of Greek money that we saw at the height of the crisis is by no means irrelevant.

A BBC journalist, speaking in Athens just as the referendum results were reported, considered the...