“If you look over the entire … last 66 million years, the only event that we know of … that has a massive carbon release and happens over a relatively short period of time is the PETM. We actually have to go back to relatively old periods. Because in the more recent past, we don’t see anything [even remotely] comparable to what humans are currently doing.” Richard Zeebe of the University of Hawaii in a recent paper published in Nature.
(Annual human carbon emissions are about 150 times that of all the volcanoes on the Earth, 10 times faster than a hothouse extinction that occurred 55.8 million years ago. Image source: La Rosa Rossa.)
Let’s be very clear. The human fossil fuel emission is outrageous and unprecedented on geological timescales. An insult the Earth has likely never seen before. For the pace at which we are emitting carbon into the atmosphere is just flat out insane. We’ve known this for some time because the best of science can’t find any time in all of Earth’s geological history that produces a rate of atmospheric carbon accumulation equal to the one that’s happening now.
However, a new study recently published in Nature now sheds more light on this rather difficult and scary topic. But in order to find an event that is even remotely comparable to the current human greenhouse gas emission, scientists had to look far back into deep time. All the way back through a period when the last of the Dinosaurs were dying off about 55-66 million years ago.
During this time we find evidence of the most recent Hothouse Mass Extinction Event in the geological record. We call this event the Paleocene-Eocene Thermal Maximum or PETM because it’s an extreme period of rapid warming that occurred at the boundary between these two periods of Earth History about 55.8 million years ago.
The PETM Hothouse Extinction
The PETM was pretty amazingly bad. It set off a mass extinction in the oceans which wiped out half of all shellfish through the varied impacts of anoxia, acidification and coral bleaching. Its heat forcing was enough to completely reverse ocean circulation and set up a stratified ocean state. Peatlands and forests went up in mass conflagrations. Terrible insect plagues swept the globe. The related extreme surface temperatures forced a mass poleward migration and widespread genetic alteration of mammals which were eventually reduced to dwarfism.
(Earlier studies estimated PETM emissions rates in the range of 1.7 billion tons of carbon per year. A new Nature study finds PETM emissions to be even lower at 1.1 billion tons of carbon per year. This compares to a current human emission of 10 billion tons of carbon per year. A rate of emission that could jump to as high as 25 billion tons of carbon per year by mid Century unless fossil fuel use is curtailed. It’s worth noting that the ‘slow but steady’ PETM emissions above represent one of the most rapid periods of warming in Earth’s geological history. Image source: Climate Crocks.)
It was a rough and wrenching time of change and difficulty for pretty much all of life on Earth. But what the new study finds and confirms is that the rate of atmospheric carbon accumulation during that extinction period, though enough to cause seriously dramatic climate shifts, was much, much slower than what we see now.
A Human Hothouse Extinction Would be Far Worse
On average, over the PETM extinction event, rates of atmospheric carbon accumulation were found to be in the range of about 1.1 billion tons per year. By comparison, human carbon emissions during 2014 were about ten times this level at around 10 billion tons of hothouse gas hitting the atmosphere. As such, the new study finds that the velocity of the human carbon emission exceeds that of the Paleocene-Eocene hothouse extinction event by an order of magnitude (x10).
Study authors found that the large carbon emission occurred over the course of about 4,000 years. This spike in atmospheric carbon coincided with an approximate 5 degree Celsius spike in global temperatures in the 4,000 to 12,000 year time period. This implies a rate of warming of at most around 0.12 degrees Celsius every 100 years (or as little as 0.04 degrees Celsius per Century). Other estimates put the rate of PETM warming at around 0.025 C per Century. Expected human warming between 1 and 5 degrees Celsius this Century is therefore about 10 to more than 200 times faster than during the PETM extinction event given the best available current scientific evidence.
Such high rates of atmospheric carbon accumulation and related global heating risk generating an event that is outside of any geological context that scientists might use to predict the human warming event’s severity.
“It means we don’t have a really good analog in the past for the massive amount of carbon we’re releasing,” Zeebe said to National Geographic. “Even if we look at the PETM and say the transition to a warmer climate may have been relatively smooth, there’s no guarantee for the future.”
In other words, if you’re adding carbon to the atmosphere at a rate ten times faster than during one of the most remarkable warming events in Earth’s History, then the pace of wrenching geophysical changes and the extinction pressure on organisms is going to be far, far greater. Something that is certainly worse than the PETM and that may even exceed the terrible losses seen during the Permian Mass Extinction if we don’t get a handle on our fossil fuel emissions soon.
Hat tip to DT Lange
Hat tip to Colorado Bob