In the hottest parts of the world, high temperatures and humidity will exceed the threshold for even the young and healthy to survive for extended periods as the planet warms, a study says. Heat waves can already be deadly for the most vulnerable people — but in a warming world, temperatures and humidity will exceed the threshold for even the young and healthy to survive every year, new research published Monday suggests. . Lahore, Pakistan, already an epicenter of human diseases linked to climate change, could exceed that survival threshold for two or three weeks a year by mid-century, for example, a study in the journal Proceedings of the National Academy of Sciences found. Under the most dramatic global warming scenarios, it could take months. (Scott Dance)