In 1896, the Swedish physicist Svante Arrhenius realized that carbon dioxide (CO2) traps heat in Earth’s atmosphere — the phenomenon now called the greenhouse effect. Since then, increasingly sophisticated modern climate models have verified Arrhenius’ central conclusion: that every time the CO2 concentration in the atmosphere doubles, Earth’s temperature will rise between 2 and 5 degrees Celsius.

Still, the physical reason why CO2 behaves this way has remained a mystery, until recently.

First, in 2022, physicists settled a dispute over the origin of the “logarithmic scaling” of the greenhouse effect. That refers to the way Earth’s temperature increases the same amount in response to any doubling of CO2, no matter the raw numbers.

Then, this spring, a team led by Robin Wordsworth of Harvard University figured out why the CO2 molecule is so good at trapping heat in the first place. The researchers identified a strange quirk of the molecule’s quantum structure that explains why it’s such a powerful greenhouse gas — and why pumping more carbon into the sky drives climate change. The findings appeared in The Planetary Science Journal.

“It’s a really nice paper,” said Raymond Pierrehumbert, an atmospheric physicist at the University of Oxford who was not involved in the work. “It’s a good answer to all those people who say that global warming is just something that comes out of impenetrable computer models.”

To the contrary, global warming is tied to a numerical coincidence involving two different ways that CO2 can wiggle.

“If it weren’t for this accident,” Pierrehumbert said, “then a lot of things would be different.”

...read more at quantamagazine.org