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Millions of people around the world could be exposed to dangerous levels of heat stress - a dangerous condition which can cause organs to shut down.

Many live in developing countries, and do jobs that expose them to potentially life-threatening conditions.

These include being out in the open on farms and building sites or indoors in factories and hospitals.

Global warming will increase the chances of summer conditions that may be "too hot for humans" to work in.

When we caught up with Dr Jimmy Lee, his goggles were steamed up and there was sweat trickling off his neck.

An emergency medic, he's labouring in the stifling heat of tropical Singapore to care for patients with Covid-19.

There's no air conditioning - a deliberate choice, to prevent the virus being blown around - and he notices that he and his colleagues become "more irritable, more short with each other".

And his personal protective equipment, essential for avoiding infection, makes things worse by creating a sweltering 'micro-climate' under the multiple layers of plastic.

"It really hits you when you first go in there," Dr Lee says, "and it's really uncomfortable over a whole shift of eight hours - it affects morale."