The number of extremely hot days every year when the temperature reaches 50C has doubled since the 1980s, a global BBC analysis has found.

They also now happen in more areas of the world than before, presenting unprecedented challenges to human health and to how we live.

The total number of days above 50C (122F) has increased in each decade since 1980. On average, between 1980 and 2009, temperatures passed 50C about 14 days a year.

The number rose to 26 days a year between 2010 and 2019.

In the same period, temperatures of 45C and above occurred on average an extra two weeks a year.

"The increase can be 100% attributed to the burning of fossil fuels," says Dr Friederike Otto, associate director of the Environmental Change Institute at the University of Oxford.