I absolutely love the questions about doomsday.
The Earth has experienced five mass extinctions before the one we are living through now, each so complete a slate-wiping of the evolutionary record it functioned as a resetting of the planetary clock, and many climate scientists will tell you they are the best analog for the ecological future we are diving headlong into.
Unless you are a teenager, you probably read in your high-school textbooks that these extinctions were the result of asteroids. In fact, all but the one that killed the dinosaurs were caused by climate change produced by greenhouse gas. The most notorious was 252 million years ago; it began when carbon warmed the planet by five degrees, accelerated when that warming triggered the release of methane in the Arctic, and ended with 97 percent of all life on Earth dead.
We are currently adding carbon to the atmosphere at a considerably faster rate; by most estimates, at least ten times faster. The rate is accelerating. This is what Stephen Hawking had in mind when he said, that the species needs to colonize other planets in the next century to survive, and what drove Elon Musk, last month, to unveil his plans to build a Mars habitat in a few decades.
Humans, like all mammals, are heat engines; surviving means having to continually cool off, like panting dogs. For that, the temperature needs to be low enough for the air to act as a kind of refrigerant, drawing heat off the skin so the engine can keep pumping. At seven degrees of warming, that would become impossible for large portions of the planet’s equatorial band, and especially the tropics, where humidity adds to the problem; in the jungles of Costa Rica, for instance, where humidity routinely tops 90 percent, simply moving around outside when it’s over 105 degrees Fahrenheit would be lethal. And the effect would be fast: Within a few hours, a human body would be cooked to death from both inside and out.
At 11 or 12 degrees of warming, more than half the world’s population, as distributed today, would die of direct heat. Things almost certainly won’t get that hot this century.
The air conditioning will not be available to all, working in fields will be almost impossible and there will be food shortages and droughts. when ice melts there will be new threats exposed to this world like the old diseases which has been burried below the ice for 100s of years. People will migrate from topics to the north and with them bring a new set of diseases that have not been native to those areas already. Smog will be a regular in areas that have never seen it before and lungs diseases will claim more lives.
But we are humans and i have faith in ourselves that we will not let humanity reach this far, we are likely to destroy each other well before all of above happens. we have seen signs of impatience and eager to fight and kill each other and it is only growing. so we may not live to see the nature destroy us, we will do it ourselves well before that.
