global warming in the paleocene epoch -- 11/20/19
Today's selection -- from The Ends of the World by Peter Brannen. The Paleocene-Eocene Thermal Maximum:
"'The Paleocene and Eocene was a time of very chaotic swings in climate,' [Steve] Brusatte said as we hiked under a withering New Mexican sun over dry, dusty streambeds. This desert heat was nothing, though, compared to the global sweat lodge faced by our ancestors.
"'We know it was a really hot time, much hotter than today. And given where we're headed, we want to know what our planet's going to be like during hot times. Not only was it a lot hotter, but you have these big spikes in temperature and they last for maybe tens of thousands, or a few hundred thousand, years at most. That's why we're here studying it.' ...
"The hothouse of the early age of mammals hit its sweltering maximum 56 million years ago, when an amount of carbon roughly equivalent to today's fossil fuel reserves was released to the atmosphere and oceans over the course of less than 20,000 years. As a result, the temperature spiked 5 to 8 degrees Celsius. This is known as the Paleocene-Eocene Thermal Maximum, or PETM. The source might have been volcanoes deep in the North Atlantic, burning through huge stores of fossil fuels under the seafloor. As the carbon dioxide and methane degassed the climate would have sizzled, perhaps kicking off a feedback loop by thawing permafrost on land, which then would have released ever more carbon dioxide and methane, warming the planet even further. None of this should sound encouraging to modern ears.
"Coral reefs took a grave body blow in the PETM, while mammals, like early horses, shrank in size to beat the heat and raced poleward, where the Arctic Ocean was a tepid 76 degrees Fahrenheit. Even when the heat wave relented, the earth was still feverishly warm. Today on windswept Ellesmere Island in the Canadian high Arctic, on a barren hillside overlooking ice-choked seas, fossil tree stumps mark the former site of an Eocene swamp forest once inhabited by flying lemurs, giant tortoises, hippolike animals, and alligators. Worst-case carbon dioxide emissions and climate sensitivity models promise to return our modern planet to this Eocene steam bath.
|Earth in the Eocene.|
"One proposed cause for the high-CO2 hothouse that began in the age of dinosaurs and reigned in this early mammalian heyday is -- once again -- India. The subduction zones that dragged the island continent across the ocean, pulling it toward Asia, shoved the ocean floor down into the earth and devoured thousands of miles of carbonates laid down by dead sea life over the ages. Carbon dioxide from the consumed rock was continuously gassed out above, in a vanguard of volcanoes. When India crashed into Asia around 45 million years ago, this CO2 factory -- in operation for tens of millions of years -- shuttered its doors and the volcanoes went quiet. As the collision pushed the Himalayas into the sky, these volcanic rocks and this newborn mountain range began to weather, drawing down CO2 even further. As with the creation of the Appalachians and the Ordovician ice age 400 million years prior, when the uplift and weathering of the Himalayas began, the long, slow decline to the modern ice age was set in motion.
"Eventually Antarctica, long a lush, forested preserve, began to separate from Australia, bringing an end to the last vestige of the supercontinent Gondwana. As the southernmost continent began to grow an ice cap and cooler and dryer climates spread across the globe, the Eocene ended with a chill 34 million years ago. This transition, from the long-standing greenhouse climate to a more modern climate with ice at the poles, caused a major turnover in animal life. Bizarre mammals like the knobby-headed, rhinoceros-like brontotheres vanished at this first blush of polar ice. Grasslands and savannas familiar to us today began to spread, taking over from primeval forests. This changeover is called 'the Grande Coupure' (French for 'big break'). "