Only the most idiotic and hatefully prejudiced members of the human population of the globe can be in denial of global warming caused by greenhouse gasses emitted by our industrial civilization. 2014 was the hottest year on record, and most climate models show the heating up to be accelerating. At best politicians dither, and of course in most countries they are backed by the vast majority of people who don't want to give up the benefits of industrial civilization, much as they might whine about some of the negative consequences.
Where it will end exactly is hard to predict even with computer models, but as a rule of thumb I am going with the earth going back to conditions last seen during the Permian.
The Permian was hot, by our current standards. It ran from about 300 million to 250 million years ago. It followed the Carboniferous, which was when much of the coal and petroleum we've been burning started to from. It ended with a mass extinction, followed by the Triassic (which featured large lizards and the first dinosaurs).
The Permian is not a bad time to go back to, on the whole. In fact it was warmer (on average) than the Carboniferous, but not as hot as the Triassic. It was about 2 degrees Centigrade warmer than it's been on earth lately. Of course then, as now, some places were considerably hotter than others.
But life thrived anyway. It was an important period in the evolution of life, as amphibians began to give way to reptile-like creatures and even the earlier mammal-like creatures. In the oceans Trilobites were still in good supply, but going extinct. Seed ferns appeared, but some of the landscape might seem familiar to us, as the earliest conifers appeared. On the other hand, cockroach like insects did pretty well. If you don't like cockroaches, you won't like the New Permian.
Cockroaches should do well as things heat up, but in the evolution of life, predictions are just guesses. Maybe rats will do well. Maybe reptiles will start getting bigger again. But it won't be just a repeat of the Permian. Because I think Homo Sapiens will survive. Perhaps renamed Homo Stupidius.
Another difficult guess is how many humans will survive the coming die off. Will most of us cooperate to stay alive, with the population reduced to maybe 1 billion from the current 7 billion? I doubt that, but it is possible. I think people will cut each others throats for the last remaining air conditioned theater tickets, or grass-fed beef, or whatever else has not disappeared but reminds the survivors of the good old days.
I expect humans to evolve after the winnowing. We'll see who can take the heat. Small noses are probably out. Big noses help to cool hot air on the way to the lungs, and to retain moisture as air leaves the lungs. While cold-blooded animals will likely get bigger, humans may get smaller. Body mass, which generates heat, shrinks at a faster rate than skin surface, which helps cool the body off. Unless it is so hot that skin surface admits more heat, so it is better to be big ... in which case people will evolve to be the size of elephants. Or at least Rhinos. Which would give Republicans an advantage.
But most promising is the potential for what biologists call radiation. Not atomic radiation, but the evolutionary branching out of one life form into different niches, followed by specialization and eventually by forming new species or even whole new groups of species.
Radiation typically occurs when a dominant life form is wiped out. That is how a few mostly small mammals that had been hiding in holes came to replace the dinosaurs. A few million years later there were mammals of all sizes occupying all kinds of niches, from herbivore to omnivore to carnivore. So you might, in a million years or so, get cow-like homo species and wolf-like species and certainly sloth like species, snake like species, and maybe even bird men.
But can't we do anything to stop this disaster? Can't we save the current flora and fauna and temperature range? Clearly no. It is over. Industry won. It bought politicians and scientists and propagandists and the general public. They delayed and weaseled and made money on the side selling solar cells and wind mills.
So adapt or perish. Of course, it make take a few hundred generations to see what type of humans will ultimately emerge from the die off.
Of course I could be wrong. We could be headed to the Devonian instead. Average temperature 6 degrees Centigrade above the current era. Giant insects and scorpions dominate a landscape of primitive plants, with a few amphibians walking around. Happy hunting. Or avoiding predators.