Graph showing 20,000 years of years of temperature rise during the Paleocene-Eocene Thermal Maximum (PETM) event, compared with the current temperature rise caused by anthropogenic global warming. Graphic: Robert Scribbler

[Only the last 66 millions years? More like the entire 4+ billion year history of Earth. There has never been a time when the great biogeochemical cycles of carbon, phosphorus, nitrogen, and sulfur, on which the entire biosphere depends, have been disrupted simultaneously, on the scale of megatons and gigatons per year. –Des ]

By Chris Mooney
21 March 2016

(Washington Post) – If you dig deep enough into the Earth’s climate change archives, you hear about the Paleocene-Eocene Thermal Maximum, or PETM. And then you get scared.

This is a time period, about 56 million years ago, when something mysterious happened — there are many ideas as to what — that suddenly caused concentrations of carbon dioxide in the atmosphere to spike, far higher than they are right now. The planet proceeded to warm rapidly, at least in geologic terms, and major die-offs of some marine organisms followed due to strong acidification of the oceans.

The cause of the PETM has been widely debated. Some think it was an explosion of carbon from thawing Arctic permafrost. Some think there was a huge release of subsea methane that somehow made its way to the atmosphere — and that the series of events might have been kickstarted by major volcanic eruptions.

In any case, the result was a hothouse world from pole to pole, some 5 degrees Celsius warmer overall. But now, new research suggests, even the drama of the PETM falls short of our current period, in at least one key respect: We’re putting carbon into the atmosphere at an even faster rate than happened back then.

Such is the result of a new study in Nature Geoscience, led by Richard Zeebe of the University of Hawaii at Manoa, and colleagues from the University of Bristol in the UK and the University of California-Riverside.

“If you look over the entire Cenozoic, the last 66 million years, the only event that we know of at the moment, that has a massive carbon release, and happens over a relatively short period of time, is the PETM,” says Zeebe. “We actually have to go back to relatively old periods, because in the more recent past, we don’t see anything comparable to what humans are currently doing.” [more]

What we’re doing to the Earth has no parallel in 66 million years, scientists say

ABSTRACT: Carbon release rates from anthropogenic sources reached a record high of ~10 Pg C yr−1 in 2014. Geologic analogues from past transient climate changes could provide invaluable constraints on the response of the climate system to such perturbations, but only if the associated carbon release rates can be reliably reconstructed. The Palaeocene–Eocene Thermal Maximum (PETM) is known at present to have the highest carbon release rates of the past 66 million years, but robust estimates of the initial rate and onset duration are hindered by uncertainties in age models. Here we introduce a new method to extract rates of change from a sedimentary record based on the relative timing of climate and carbon cycle changes, without the need for an age model. We apply this method to stable carbon and oxygen isotope records from the New Jersey shelf using time-series analysis and carbon cycle–climate modelling. We calculate that the initial carbon release during the onset of the PETM occurred over at least 4,000 years. This constrains the maximum sustained PETM carbon release rate to less than 1.1 Pg C yr−1. We conclude that, given currently available records, the present anthropogenic carbon release rate is unprecedented during the past 66 million years. We suggest that such a ‘no-analogue’ state represents a fundamental challenge in constraining future climate projections. Also, future ecosystem disruptions are likely to exceed the relatively limited extinctions observed at the PETM.

Anthropogenic carbon release rate unprecedented during the past 66 million years

22 March 2016 ( – “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.”

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 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.

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). [more]

Ten Times Faster Than a Hothouse Extinction — Human Carbon Emission is Worst in at Least 66 Million Years


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