Nearly 25% of world population exposed to deadly city heat

Concrete and asphalt as well as scarce vegetation in urban areas lead to higher temperatures, study shows

Exposure to deadly urban heat has tripled since the 1980s, and now affects nearly a quarter of the world's population, a study has found.

Scientists put the worrying trend down to the combination of rising temperatures and growing numbers of people living in urban areas, and warned of its potentially fatal impact.