Imagine a world in which half of the planet was incompatible with human life. Now imagine a world in which three-quarters of the planet would be lethal to human life. The first is the world in 2100 if we implement drastic reductions of greenhouse gas emissions. The second is what we're left with if we don't.
Incompatible with human life refers to 'wet bulb 35.' That's where temperatures exceed 35 degrees Celsius and humidity approaches 100 per cent. Where excessive heat and humidity combine the body overheats. Sweat no longer evaporates and you basically cook yourself alive until you're not. It's a matter of hours if you're young and healthy and resting in the shade.
At that point, even the fittest young adult is unlikely to survive more than a few hours before fatally overheating. But lower wet-bulb temperatures can still claim the lives of the elderly or infirm. Deadly heat waves in India and Pakistan that killed 5,000 people in 2015 only produced wet-bulb temperatures in the range of 29-31 °C.Mora's team of researchers crunched the data from more than 900 papers and the end result was pretty grim. If we slash greenhouse gas emissions, half of the world will be incompatible with human life by 2100. That goes for plenty of other species too, both terrestrial and marine, plant and animal. That's first prize, the grand prize. If we fail we get hyper-dystopia - three quarters of the Earth will be lethal to human life.
I've linked to the paper. It's only a 7-page summary, complete with all the charts and data you'll need.