Not to beat a dead horse, but carbon dioxide emissions are venting into the atmosphere at extremely unprecedented rates. Now, a new study published in Nature Geoscience puts the current rate of greenhouse gas emissions into some of the starkest terms yet.
About 56 million years ago—10 millions years after dinosaurs went extinct—a massive amount of carbon was released into the atmosphere, causing temperatures to rise 5° Celsius. Scientists have started focusing on this era, known as the Paleocene-Eocene thermal maximum (PETM), as a way of gauging how 21st century carbon emissions might impact life on Earth. What the researchers have determined in their new study is highly disconcerting: That the epic carbon venting 56 million years ago may have been around 10 times slower than today's rate.
To put this in perspective, in 2014 annual carbon emissions reached a new record of about 37 billion metric tons of carbon dioxide. During the PETM, researchers estimate that the sustained carbon dioxide release had to be less than four billion metric tons per year.
This has created what Richard Zeebe, professor at the University of Hawai'i-Mānoa School of Ocean and Earth Science and Technology and lead author of the study, called a "no-analogue" state.
"Because our carbon release rate is unprecedented over such a long time period in Earth's history, it also means that we have effectively entered a 'no-analogue' state," he said in a statement. "This represents a big challenge for projecting future climate changes because we have no good comparison from the past."
According to the authors, this is especially worrisome from an adaptation perspective, as plants and animals require extended time periods to effectively adapt to new and unfamiliar conditions.
“Ecosystems need time to adjust,” said Zeebe. “We’re doing it faster and most likely the consequences are going to be more severe.”
"Everyone is focused on what happens by 2100. But that's only two generations from today. It's like: If the world ends in 2100 we're probably OK!" said Zeebe. "But it's very clear that over a longer timescale there will be much bigger changes."
The researchers were able to determine Earth's climate millions of years ago by examining deep sea sediments and their chemical and biological markers, in this case using a 24-centimeter piece of sediment from a borehole in New Jersey. The sample, which included sands, clays, and silts from an ancient offshore sea, is believed to represent the PETM era. In order to get the data they needed, the researchers developed a new method that allowed them to calculate how fast carbon was being released and how fast the Earth's surface warmed over a period of at least 4,000 years.
Dr. Andy Ridgwell, a professor in the department of earth sciences at the University of California, Riverside and author on the study, told me that the study is a reminder that we still have about another 0.8° Celsius "programmed" into the climate system because the ocean takes so much longer to warm up than the land and atmosphere. He said this discrepancy is the basis of their analysis and that they were "looking for a 'lag' between warming and indicators of carbon release," but since they saw no lag they "concluded that the carbon release and warming occurred much slower than it is occurring today."
The planet has already warmed about 1° Celsius since pre-industrial times.
As an article in Science Magazine about the study points out, there are still a lot of questions regarding the exact accuracy of the research and what it means for all the variables in question. Furthermore, the source of the massive carbon emissions leading to the changes remains a mystery (unlike in the present day, where humans are the obvious culprit). Potential sources include the rapid melting of permafrost, the impact from a comet, massive volcano eruptions, or, more likely than not, some combination of cascading events.
It's this notion of positive feedbacks—in which warmer temperatures create new sources of carbon that in turn create warmer temperatures—that keeps many climate change scientists up at night.
James C. Zachos, an earth and planetary sciences professor at UC-Santa Cruz and author on the study, told me that the planet will react with both physical and biological feedbacks in positive and negative ways.
"For example, disappearing ice makes the planets surface less reflective of solar energy, a positive feedback," he said. "The question is whether the positive feedbacks, which tend to amplify change, will react more quickly then the negative feedbacks, which tend to damp and ultimately reverse the change. I suspect the answer is that initially the amplifying feedbacks will react more quickly, and exasperate warming and acidification. This has has a lot to do with the rapid rate of change."