Courtesy National Geographic
Carbon is pouring into the atmosphere faster than at any time in the past 66 million years—since the dinosaurs went extinct—according to a new analysis of the geologic record. The study underscores just how profoundly humans are changing Earth’s history.
The carbon emissions rate is ten times greater today than during the prehistoric hot period that is the closest precedent for today’s greenhouse warming.
That period, known as the Paleocene-Eocene Thermal Maximum (PETM), was marked by a massive release of the Earth’s natural carbon stores into the atmosphere. (It’s not clear what caused the PETM, but volcanic eruptions and methane gas release are suspects.) The excess carbon triggered a 5°C (9°F) temperature increase, along with drought, floods, insect plagues, and extinctions. (Read more about this period of “Hothouse Earth.”)
Today, fossil fuel burning and other human activity release 10 gigatons of carbon annually. The PETM transition, 55.8 million years ago, caused massive changes in where plants and animals lived, the rapid evolution of some species, and extinction of others.
Half of all single-celled shelled organisms on the sea floor were wiped out, but many microorganisms on the ocean surface flourished during the PETM and expanded their habitats. The new study suggests that today’s marine life may not be so lucky, wrote geologist Peter Stassen of the University of Leuven in an editorial accompanying the new research. During the PETM, those organisms may have had time to adapt through migration or evolution—time that won’t be available to modern sea life.
The new estimate of the rate of carbon release at the PETM onset is similar to that found in 2011 by a team led by Pennsylvania State University. The Penn State group based their sediment analysis on what is known as an “age model;” they dated a sediment core sample drilled in Norway based on physicists’ recreation of the rhythms of Earth’s orbit around the sun. Slight changes in that orbit leave a pattern of iron concentrations in the sediment.
Lee Kump, head of geosciences at Penn State, said he was “heartened” that the new approach arrived at numbers in line with his team’s estimates, although he noted both papers come to the same grim conclusion.
“The lesson for society is the same,” he said. “We are now exceeding by an order of magnitude the rate of carbon release during one of the most remarkable global warming events in Earth’s history.”
