Peter Brannen writes:

We live on a wild planet, a wobbly, erupting, ocean-sloshed orb that careens around a giant thermonuclear explosion in the void. Big rocks whiz by overhead, and here on the Earth’s surface, whole continents crash together, rip apart, and occasionally turn inside out, killing nearly everything. Our planet is fickle. When the unseen tug of celestial bodies points Earth toward a new North Star, for instance, the shift in sunlight can dry up the Sahara, or fill it with hippopotamuses. Of more immediate interest today, a variation in the composition of the Earth’s atmosphere of as little as 0.1 percent has meant the difference between sweltering Arctic rainforests and a half mile of ice atop Boston. That negligible wisp of the air is carbon dioxide.

Since about the time of the American Civil War, CO2’s crucial role in warming the planet has been well understood. And not just based on mathematical models: The planet has run many experiments with different levels of atmospheric CO2. At some points in the Earth’s history, lots of CO2 has vented from the crust and leaped from the seas, and the planet has gotten warm. At others, lots of CO2 has been hidden away in the rocks and in the ocean’s depths, and the planet has gotten cold. The sea level, meanwhile, has tried to keep up—rising and falling over the ages, with coastlines racing out across the continental shelf, only to be drawn back in again. During the entire half-billion-year Phanerozoic eon of animal life, CO2 has been the primary driver of the Earth’s climate. And sometimes, when the planet has issued a truly titanic slug of CO2 into the atmosphere, things have gone horribly wrong.

Today, humans are injecting CO2 into the atmosphere at one of the fastest rates ever over this entire, near-eternal span. When hucksters tell you that the climate is always changing, they’re right, but that’s not the good news they think it is. “The climate system is an angry beast,” the late Columbia climate scientist Wally Broecker was fond of saying, “and we are poking it with sticks.”

The beast has only just begun to snarl. All of recorded human history—at only a few thousand years, a mere eyeblink in geologic time—has played out in perhaps the most stable climate window of the past 650,000 years. We have been shielded from the climate’s violence by our short civilizational memory, and our remarkably good fortune. But humanity’s ongoing chemistry experiment on our planet could push the climate well beyond those slim historical parameters, into a state it hasn’t seen in tens of millions of years, a world for which Homo sapiens did not evolve. [Continue reading…]