The third most popular video of 2019 presents a frightening truth: The best-case scenario of climate change is that the world gets just 2°C hotter, which scientists call the "threshold of

The third most popular video of 2019 presents a frightening truth: The best-case scenario of climate change is that the world gets just 2°C hotter, which scientists call the "threshold of catastrophe".

Why is that the good news? Because if humans don't change course now, the planet is on a trajectory to reach 4°C at the end of this century, which would bring $600 trillion in global climate damages, double the warfare, and a refugee crisis 100x worse than the Syrian exodus.

David Wallace-Wells explains what would happen at an 8°C and even 13°C increase. These predictions are horrifying, but should not scare us into complacency. "It should make us focus on them more intently," he says.

David Wallace-Wells is a national fellow at the New America Foundation and a columnist and deputy editor at New York magazine. He was previously the deputy editor of The Paris Review. He lives in New York City.