City nights will get hotter

It's 3am, you have long since thrown off the duvet but still cannot sleep. Another hot, sticky and sleepless night. But they will occur more often in future - especially in cities - scientists warned yesterday.

Urban air is generally hotter than country air because fields and forests absorb less heat during the day. In cities, concrete and asphalt retain heat at night after vehicles and buildings have warmed the air.

With levels of carbon dioxide - the gases emitted by cars - climbing, the 'urban heat island' effect is set to increase.

A doubling of carbon dioxide levels in the atmosphere could triple the warming effect, said Richard Betts, of the Met Office. Apart from causing more sweaty nights for city dwellers, it will also have an impact on health, he told New Scientist.

Last year's heatwave across Europe, for example, caused more than 20,000 deaths.