End of an Era – I mean “Epoch”
I never memorized the names of the eras and the epochs used to describe geologic time, but I’ve heard several references recently to the idea that scientists are considering calling an end to the current epoch (the Holocene) and starting a new one, based on the profound impact that humankind has had on the planet (to be called the Anthropocene).
It is certainly true that we’ve put a permanent end to the “natural” world; we’ve put a period at the end of that one and begun a new sentence.
As Bill McKibben points out, we’re finding PCBs in the arctic, and over 140 synthetic chemicals in our blood streams. There is no going back to what was once “the natural world.” What there is, on the contrary, is the opportunity to change our course towards full-scale ecological destruction before it’s too late.
The best paper I’ve read about this deep climate history- probably the best paper I’ve read by Hansen – is “Paleoclimate Implications for Human-Made Climate Change.”
While we haven’t yet left behind the range of climate in a typical Milankovich cycle within the Quaternary period… We are clearly moving into a climate that will differ vastly from anything seen in the past 2.5 million years.
Moreover, within the Holocene itself there was nothing spectacularly different from what was seen within the Pleistocene, other than humans developing industrial agricultural society and beginning the development of human society and human culture… but they called that the “Holocene,” just because we were there doing things.
The Quaternary period itself was differentiated from the Neogene period because of the glaciation cycles – the ice age and the interglacials. It was too warm in the Neogene period for the Milankovich cycle to force glaciers nearly as far South… the net change in global temperatures wasn’t as severe. If that marked the distinction of the Quaternary period… then it seems with our present warming that we should be considering ending the period, not the epoch, and calling the new Period the anthropocene.
Doubtless there will be more radical changes to come as more radical climate changes make themselves apparent.
It’s terribly interesting stuff.
I just hope we’re around long enough such that all this matters.
You never cease to amaze me, btw.
Craig,
I’ll admit that here that I’ve always had a childlike enthusiasm for paleontology. I really can’t take just any topic and respond on that level… but I can go a lot further into this one if you’re interested.
Sure, I’m interested.
What would you like to know?
Oh, I would say anything that relates paleontology to our current issues vis-a-vis our environment.
Craig,
Sorry it took me so long to respond. It’s been hectic, and this wasn’t a simple request. First of all, how much do you understand about the glaciation cycle? The ice age/thaw cycle that has been caused by the Milankovitch cycle in our orbit?
That’s probably a good place to start…
It didn’t actually take place until relatively recently – if there’s too much CO2 in the atmosphere, it doesn’t work (here’s looking at you, future planet)… but of course we have to question how much of a benefit an ice age would have been to future human societies.
😉
The Milankovitch cycle is a wobble of our orbit. Imagine a spinning top that is just starting to loose angular momentum but still hasn’t fallen. The top “wobbles” (precesses) in a circular pattern around a point. That’s how our planet’s axial tilt works, the axis is currently off center at ~23.4 degrees, and that precession takes roughly 26000 years.
The orbit itself is an off-center ellipse, which I’m sure you know. The axis of the ellipse of the orbit itself gradually revolves around the sun as well, in a process called “apsidal precession” (which takes about 134,000 years). The two precessions combine to form a glaciation cycle of ~21,000 – 22,000 years.
So let’s begin at this… before we get more complex.
If the Earth’s orbit is an off-center ellipse, then there is a point when it is closest to the sun (perihelion) and a point when it is furthest from the sun (aphelion).. Right now, perihelion falls between January 2 and January 7, while aphelion falls between July 2 and July 7… so the solar constant in early Jan is around 1.41 kW/m2, while the solar constant in early July is ~1.32 kW/m2…
While it is not intuitive, this actually means that the NORTHERN hemisphere has greater total insolation than the southern hemisphere. Because the orbit speeds up as it gets closer to the sun, and slows down as it gets further away (think of the orbit of a comet – this is similar, just much less extreme). So right now the Northern hemisphere has roughly 3 more days of spring and 5 more days of summer than the Southern hemisphere (and the obvious inverse – 3 less days of autumn and 5 less days of winter. While the Southern hemisphere has more insolation in its summer than the Northern hemisphere has in our summer, the difference between the two is nowhere near as great as the additional time spent facing the sun.
So right now we are quite near the point in our orbital cycle in which the Northern hemisphere gets the greatest amount of warming from the Sun (that would have been when aphelion fell on the summer solstice, ~750 years ago), while the Southern hemisphere gets the least.
The glaciation cycle revolves around the movement of ice in the Northern hemisphere – since that’s where all the land (that is not covered by the Antarctic Ice Sheet) is found.
The great Northern conifer forests can survive in the far North, surviving with little light and in the face of extreme cold. These drop a constant layer of needles into the frozen Northern ground, which never fully break down before they are buried by new needlefall. Hence these constantly fix carbon and sequester it into the ground. Within the permafrost, there is some anaerobic breakdown of the needles, but the gasses – both CO2 and CH4 – are trapped in the frost. It’s estimated that some of the Northernmost forests have biomatter up to 60 meters deep. The grasses and shrubs of the Russian tundra had similar effects – again with biomass being buried into the permafrost in a manner that constantly fixed the carbon. This obviously has the effect of gradually lowering the CO2 level in the atmosphere.
When the orbital cycle begins causing more extreme climate variations, harsher cold winters, and longer periods of dark for the Northern climates, the regions of permafrost creep south slightly, and the regions in which the Northern flora serve to fix CO2 expands… and we have lower temperatures, also serving to expand the permafrost, and eventually the ice follows, burying the remains of the Northern forests as the CO2 level drops, and the orbital cycle continues to reduce the net insolation of the North and advantage the expansion of the permafrost. In the Southern hemisphere, even with the increase in insolation, there is still growth in glaciers and an advance north, because the net CO2 level in the atmosphere is gradually dropping, but the advance is not nearly as rapid nor as far North.
The cycle continues for several centuries – perhaps even a millennium – after the orbital pattern reverses and begins to advantage the Northern hemisphere again, simply due to system inertia… but once the system slows down and the ice begins to melt off, you have all the fun feedbacks that we’re talking about today – with melting permafrost releasing billions of tons of CO2 and CH4, allowing rapid heating which melts more ice, allowing lower albedo which thaws more permafrost, releasing more trapped carbon. The Northern flora retreats, replaced with trees that drop leaves that are not protected from the microbes with heavy wax… and the reduced diversity of life that survived the last ice age begins to migrate north and evolve into much greater diversity with much more land to compete for… and this continues for a few centuries past the point when the orbit again lines up with the Northern summer solstice at aphelion.
There is another orbital cycle – that of the essentricity (non-roundnesss) of the ellipse of the Earth’s orbit. This more or less is a loose 100,000 year cycle (there are so many shifting gravitational influences from the other planets that it varies), and this plays a role in the severity of the glaciation cycle – as the difference between the length of summer and winter will change based on the essentricity of the orbit.
There’s also a wobble in the axial tilt itself, which wobbles between a maximum of 24.5 degrees and a minimum of 22.1 degrees. That cycle takes 41,000 years.
Then finally there’s a cycle where the plane, or the “inclination” of the orbit changes with respect to the plane of the solar system. The plane of the solar system itself has more solar dust, which likely causes us to experience slightly less insolation the closer the plane of our orbit aligns with the plane of the solar system, and more the further away. This cycle is ~70,000.
All told, the other orbital perturbations add up to have an impact that is either warming or cooling, such that with each 21,000 year precession cycle, there is either a net gain or a net loss of ice mass.
So that’s glaciation in a nutshell… obviously there’s more, but that’s what pertains to climate change… What’s very interesting is that it’s relatively new. ~2.5 million years ago, before the Quaternary Period began, this didn’t happen. There was a great Antarctic Ice Shelf, and the Greenland ice sheet… but the ice didn’t MARCH up and down the the parallels like a slowly progressing football game. There was sufficient CO2 in the atmosphere that the difference in insolation for the Northern Hemisphere wasn’t enough to extend the permafrost southward enough to start the cycle. The ice expanded in the winter and contracted in the summer, but there weren’t “Ice ages”.
Prior to the Quaternary period, was the Neogene period (all part of the Cenozoic Era). At the beginning of this period, North and South America were joined, and the ocean no longer saw a current of free-flowing warm water flowing around the equator. This caused our more modern “conveyor” currents to form, and it reduced the temperature of the ocean surface considerably, which allowed arctic ice to start forming in the deep winter, and allowed the beginning of the Greenland Ice Sheet.
Prior to the Neogene was the Paleogene period. This was the first period of the Cenozoic Era. Evolutionary, this is when mammals first evolved, and plant life thrived. On a climate basis, this is the period which represents a recent maximum in global temperatures. When the island of India smashed into mainland Eurasia – forming the Himalayan mountains – this was an extremely aggressive period of geological activity. As such, there was a prolonged period (millions of years) where the rate of CaCO3 conversion into CaO + CO2 vastly exceeded the fixation of CO2 into CaCO3 and the sequestration of CO2. So at the beginning of the Paleogene period (~60 million years ago), there was a CO2 concentration of ~1200 ppm, and we had things like tropical plants growing in Antarctica. It was a hot wet world.
But from the very start of the Cenozoic Era we’ve been seeing gradual cooling of the Earth accompanying a gradual reduction in CO2, because the CO2 has been gradually sequestered into soils and methane hydrate structures and methane reservoirs and crude oil and tar and coal… etc… So less carbon was yielding lower temperatures, and we were likely on a path towards a third iteration of “Snowball Earth” (possibly occurring in as little as a few million years), until mankind started digging up those long sequestered carbon deposits and burning them. So now we’re very quickly unwinding the clock, and we may well see carbon levels similar to those seen in the Paleogene period within only 500 years of the start of the industrial revolution. Unwinding ~20 million years of climate history (a time frame that is VERY easy for plants and animals to evolve to adapt to vastly different climates) in 0.0005 million years (a time frame in which only microbiology, molds, insects, and rodents really have a chance to significantly evolve).
(The evolution time frame and the rising sea levels are, in my opinion, the only compelling reasons to subsidize mitigation vs strictly offsetting accommodation strategies – though no-matter what we really will need a tremendous amount of accommodation for even the most aggressive mitigation strategies.)
In the third paragraph, I used the term “constantly off center at ~23.4 degrees”, when I mean to say “currently off center at ~23.4 degrees”.
Sorry, I was JUST responding when I saw this. Please see: http://2greenenergy.com/2014/10/27/climate-disrupution-anthropocene/.
I made that change in your comment, btw.
Thanks Craig.
There’s actually quite a few errors now that I re-read it… It could have done with a proofreading stage before posting, but it took quite a bit longer than I thought it would to get out… so it is what it is.
If you could make a few minor edits:
In the 10th paragraph, the last sentence starts with “Even with increased insolation…” that was supposed to be “In the Southern hemisphere, even with increased…”
Then the next paragraph starts with “The cycle continues for centuries, even a millineial”… that was supposed to be “millennium”.
… I should let it go. I probably would have proofed it had I thought you were going to link to it.
🙂
I was just rushing off, I had taken too long and Rochelle was letting me know I had taken too long.
🙂
Got ’em. Thanks. I’m sure you’ll see my new post on the subject.