There are plenty of tipping points like this: The Amazon, for instance, appears to be drying out and starting to burn as temperatures rise and drought deepens, and without a giant rainforest in South America, the world would function very differently. In the North Atlantic, says Mann, "we're ahead of schedule with the slowdown and potential collapse" of the giant conveyor belt that circulates warm water toward the North Pole, keeping Western Europe temperate. It's tipping points like these that make climate change such a distinct problem: If we don't act quickly, and on a global scale, then the problem will literally become insoluble. We'll simply move into a dramatically different climate regime, and on to a planet abruptly and disastrously altered from the one that underwrote the rise of human civilization. "Every bit of additional warming at this point is perilous," says Mann.
Another way of saying this: By 2075 the world will be powered by solar panels and windmills – free energy is a hard business proposition to beat. But on current trajectories, they'll light up a busted planet. The decisions we make in 2075 won't matter; indeed, the decisions we make in 2025 will matter much less than the ones we make in the next few years. The leverage is now.
What happens in the next 4 years has huge consequences. This is the end game, and we need to start acting like it. Everything is on the line, it's time to go all-in. This is our challenge as organisers, mobilisers and campaigners. If our organisations do not rise to this moment, our civilisation will perish.