Scientific American: The last time the Earth enjoyed greenhouse gas levels like those of today was roughly 4 million years ago, during an era known as the Pliocene. The extra heat of average temperatures as much as 4 degrees Celsius warmer turned the tropical oceans into a nice warm pool of bathwater, as noted by new research published in Nature on April 4.
By analyzing the ratio of magnesium and calcium in the shells of microscopic animals found in long cores of mud from the deep ocean, the researchers confirmed...