The anthropocene

 First let's define a couple of terms.  We are at present in an ice age.  We are in a warm period within this ice age which is, so far, 2.75million years old.  Within this ice age there have been many warm periods.  At the beginning of this ice age, the cycle period was about 41,000 years.  Now, and for the last half, it has been about 100,000 years.  Our present warm period has been called the Holocene and started about 20,000 years ago.  The previous warm period is called the Eemian.  The start of the Holocene is defined by when the most recent Glacial (or glacial period if you like) was at it's maximum and then began to decline.    It may be more useful to define the start of the Holocene at about 12,000 years ago when melting really got under way.

Now we are arguing that we are in a new period, called the Anthropocene because man has taken control of the climate.  Using the word control may be a little optimistic.  We have changed the climate and are going to change it much more but it is actually completely out of our control.  We could control the climate and many important innovations, which would be sufficient to do so have been put into place but our politicians, who have to do the heavy lifting, have been fighting such moves, screaming and shouting and dragging their heels ever since it has become apparent that we are not going to like the results from climate change.

In the past, the change from one geological period* to the next has been defined by geology.  When the assemblage of animals in a continually deposited stack of sedimentary rocks changes we define a new period. A well known example is the K/T boundary - the change from the Cretaceous to the Tertiary.  Below this we have fossils of dinosaurs and other organisms, above this, no dinosaurs and a change in the assemblage of other organisms.

*I use the word 'period' to avoid having to define epochs, ages, eras, eons and so forth. Even using the term 'period' is problimatic as it is sometimes used in formal geology.

We are now arguing about when the Anthropocene started with the consensus seeming to be a little after the Second World War, when we started to have an effect on the climate.  

The change from using the assemblage of animals in the fossil record to a using change in climate to define a new period is probably due to the belief that the past changes in animal assemblages was due to climate change.  So is it justified to say we have changed the animal assemblages that could become fossilized just after the 2nd world war. (then we will examine the climate change argument).

Well, No.  Depending on which continent you look at, the animal assemblages changed in the blink of a geological eye some time ago. The process took, at most, one or two thousand years.   In North and South America it happened about 12,000 years ago.  In Australia, about 50,000 years ago and in New Zealand, about 700 years ago.  In every case it occurred following the discovery of these areas by the "First People" who wiped out every animal that their existing technology was capable of killing and eating.  The above are just commonly known examples.  The same thing happened everywhere man first arrived.  So how about us having an effect on the climate.

There is an excellent book called Plows Plagues and Petroleum by Ruddiman that argues otherwise.  Let's go back to the glacial periods.  When you look at ice cores from both Greenland and Antartica, ocean bottom cores and some other proximal indicators, it becomes clear that when a glacial period ends, temperatures rise and ice disappears to a minimum amount and then an pretty well immediate a slide begins back toward a glacial period.  In fact the slide starts to occur a little before minimum ice as you would expect*.  It takes time for snow to accumulate and glaciers to form and for the temperature and Carbon dioxide to decrease but the slide is immediately apparent.  This is very apparent in the graphs of the most recent 4 or so glacial-interglacial cycles.  All but the most recent one.

*Carbon dioxide levels  are a good indicator of when the slide starts but it is still warm enough to melt more ice so the slide toward the next glacial (glacial period) begins a little before minimum ice.

About 8000 years ago (6000BP), we started to reverse the slide of Carbon dioxide and about 5000 years ago (3000BP) we started to reverse the slide of methane, just as man reached a population and a technology capable of doing so.  So what were we doing.  We started agriculture, using the plow which releases carbon from the soils, used fire to clear areas and started to grow rice in ponds which as with any swamp, releases methane.  We didn't reverse the slide into the next glacial but considerably slowed down the slide.

In fact, despite our effect on climate, we just reached the tipping point in which continental glaciers began to from.  Ruddiman's book says two factors tipped us over into this situation.  First there was the Black Death in the 'Old World' which again and again wiped out around a third of the population.  Huge areas which were under cultivation, reverted to forests, sucking carbon out of the air and cooling the climate.

The other event was the arrival of European man in the Americas.  We brought with us a whole range of diseases that the indiginous population had had no contact with and hence no immunity to these diseases.  Recent archeology has made it clear that the indiginous population was far larger than we thought.  For instance, in the jungles of the Amazon, vegetation rapidly took over and made it very hard to see traces of earlier civilizations.  With the advent of methods to look down with Lydar from aircraft, we see the remains of human activity in areas completely vegetated today.

In places like Virginia, the first Europeans reported stepping off their boats into fields of pumpkin, corn and beans.  50 years later this was all forest.  The people had disappeared and the forest had taken over.  All this sucked carbon out of the atmosphere and tipped us over into the accumulation of snow from year to year.

This can be seen around the high lands of Baffin Island.  In North America, this is where the snow begins to accumulate.  There is a ring of dead lichens around this area.  Despite their hardiness, the one thing lichens can't survive is a lack of light.  They are a symbiosis between a fungus and a photosynthetic organism.

Following this we were entering into an industrial revolution and reversed the fall of Carbon dioxide in the atmosphere and the snow melted back and we were off toward too much of a good thing which we are in today.  Releasing just enough carbon that is sequestered under ground to hold off the next glacial is probably a good thing.  After all, a new glacial would bulldoze New York and other cities into the sea.  But we have gone overboard and New York is likely to be drowned instead.