It has been a year of unusual weather in many parts of the world. In Europe, the south-eastern part of the continent has suffered heat, drought and forest fires while exceptional summer rainfall inundated the north-west. In the US, Texas was flooded while California roasted. Heavy monsoon rains caused devastation in South Asia. In Australia, hopes that early winter rainfall would end the worst drought in living memory have been dashed.

The usual response of climate experts, when asked whether global warming is to blame, is to say that no single "weather event" can be attributed to climate change because natural cycles have always brought storms, droughts and floods. But enough computer modelling has been done for meteorologists to warn with confidence that a warming climate will bring more extreme and more variable weather, with dry areas of the world tending to get drier while wet areas experiencing more flooding.