New climate models predict a warming surge

Article by By Paul Voosen at Science:

“In earlier models, doubling atmospheric carbon dioxide (CO2) over preindustrial levels led models to predict somewhere between 2°C and 4.5°C of warming once the planet came into balance. But in at least eight of the next-generation models, produced by leading centers in the United States, the United Kingdom, Canada, and France, that “equilibrium climate sensitivity” has come in at 5°C or warmer.”

“If the results are to be believed, the world has even less time than was thought to limit warming to 1.5°C or 2°C above preindustrial levels—a threshold many see as too dangerous to cross.”

With atmospheric CO2 already at 408 parts per million (ppm) and rising, up from preindustrial levels of 280 ppm, even previous scenarios suggested the world could warm 2°C within the next few decades.

“It mimics the ocean in fine enough detail to directly simulate eddies, honing its representation of heat-carrying currents like the Gulf Stream. Its rendering of the El Niño cycle, the periodic warming of the equatorial Pacific Ocean, looks “dead on,” says Michael Winton, a GFDL oceanographer who helped lead the model’s development. But for some reason, the world warms up faster with these improvements. Why? “We’re kind of mystified,” Winton says. Right now, he says, the model’s equilibrium sensitivity looks to be 5°C.”

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