The New York Times reports:

Since the dawn of the industrial age, our species has warmed the planet by considerably more than today’s most widely accepted estimates imply, according to a team of scientists who have gleaned detailed new information about Earth’s past climate from an unusual source: centuries-old sponges living in the Caribbean Sea.

Networks of satellites and sensors have measured the rising temperatures of recent decades with great precision. But to assess the full arc of global warming, scientists typically combine this data with 19th-century thermometer readings that were often spotty and inexact.

This is where the sponges come in. By examining the chemical composition of their skeletons, which the creatures built up steadily over centuries, the researchers have pieced together a new history of those earliest decades of warming. And it points to a startling conclusion: Humans have raised global temperatures by a total of about 1.7 degrees Celsius, or 3.1 Fahrenheit, not 1.2 degrees Celsius, the most commonly used value.

“It’s a bit of a wake-up call,” said Malcolm T. McCulloch, a geochemist at the University of Western Australia and one of the scientists who worked on the new research. [Continue reading…]