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Wednesday, October 5, 2022

Regenerative Agriculture

 What is Regenerative Agriculture?  In a word, it is a combination of various agriculture techniques that restore the fertility of the soil.  That is it in a nutshell.

There are a whole raft of benefits that flow from adopting the techniques of Regenerative Agriculture.  In no particular order:

* Water which falls on the land is retained to a large extent in the soil where it is available for the crops.  There is less evaporation and less flow of water through the soil and into the ground water.  Irrigation demands are reduced during dry periods and less water flows off the farm during wet periods.

*The carbon content of soils increases, sequestering significant carbon from the air.

*Nitrogen in the form of nitrates and Ammonium compounds are very soluable.  When applied as simple, chemical fertilizers, they dissolve in soil water and are easily washed out of the soil and into nearby streams.  Nitrogen in soils in farms practicing regenerative agriculture are held in slow-release form which are made available over the growing season to the crop.

*Costly inputs to the farm, including feed, fossil fuel, herbicides and pesticides greatly decrease, resulting in an improved bottom line for the farmer.  After a few short years using regenerative farming methods, productivity equals or exceeds what we now call conventional (commercial fertilizer driven) farming.

*Regenerative agriculture often involves more than one crop unlike some chemical farming that is a often a monoculture or sometimes an alternation between a couple of different crops.  This increases resilience to  market fluctuation.

*Farming becomes much more resilient to changes in markets and weather.

*Possibly of greatest importance, farming becomes much more interesting as the farmer uses knowledge and smarts rather than expensive inputs to run his farm.  There is no way to become depressed or worse when your bottom line improves and you are in control rather than at the mercy of outside influences.

In order to understand regenerative agriculture, there are a whole bunch of natural phenomenon that must be understood.  Again in no particular order:

*There ain't no sunshine underground.  Pretty obvious, no?  All the energy to support the underground beasties comes ultimately from photosynthesis done by some plant the lived above ground.   

*Soil organisms are really really good at scavenging all the phosphates, nitrates, sulphates and other 'ates' in their vicinity.  All they need is a source of energy in the form of plant material, which was grown  on the surface.  But if you mix-in a whole bunch of straw, sawdust etc, your plants will starve.  The soil beasties will have taken up all the goodies.  So whada you wanda do.  I don't know. Whada you wanda do (The vultures in The Jungle Book).  You put the plant material on the surface.  There it is taken into the soil in a more gradual rate and has other benefits.

*Bare soil, when hit by great big summer rain drops, puddles the fine particles in the soil and the soil surface becomes impermeable to water.  The water runs off, taking soil with it.   Rain drops hitting organic material are stopped in their tracks and seep into the ground.  When the sun comes out and dries the surface.  It is a great insulator and shields the ground below from the heat of the sun.  The soil has absorbed more water and it retains it. 

*Rich organic soil is a great sponge.  It holds lots of water.  The deeper the rich organic layer, the more water it can hold. Pure mineral soil, if fine, doesn't absorb water.  In coarse,gravely soils the water simply flows through it into the water table below - often out of the range of the roots of the plants. If a coarse soil has been filled with organic material, there is a sponge between the coarse particles of the soil to retain water.

*Most plants exude up to 30% of the energy that they collect from the sun through their roots in the form of energy rich compounds.  They don't do this out of the goodness of their non-existent heart.  That is to say, this behavior wouldn't have evolved if it wasn't worth-while for the plant. The soil organisms use these compounds and in return provide a range of benefits for the plant.  In the case of funguseseses, they exchange mineral nutrients which are either locked away chemically from the plant or are beyond the root zone of the plant for these energy rich compounds.  P is particularly important in this context.

*The part of a plant that is above ground is more or less balanced by the part that is below ground.  When you harvest/crop/graze a plant, some of the roots die back to balance the reduced above-ground part.  Think of this as the insertion of organic material deep down where it is utilized by the soil beasties and ultimately becomes humus. Some plants have roots that reach meters into the soil so this process can be building a very deep layer of top soil.

*Organic material laid on top of the soil as mulch, has all the well known benefits such as reducing evaporation, stopping rain drops from disrupting the soil and causing crusting and thereby causing more run off across the soil.  Over time.  Mulch is incorporated into the soil by a number of organisms such as beetles, earth worms and fungus which live at the boarder between the mulch and the soil.


*Fungus in the soil is your greatest ally in growing crops.  Fungus accesses nutrients in two ways and transfers these nutrients to the roots of plants in exchange for the energy rich exudates from the plant roots.  First, fungus can liberate nutrients that are  fixed in the soil and that plant roots can not liberate.  Phosphorous is notable in this context.  Some soils fix P in compounds that are not available to plant roots.  Secondly, the mycellea of funguses extend far beyond the root zone of plants.  They can mobilize and transfer nutrients to the plant from far and wide.

So what are the principles of regenerative farming.

There are a few main principles and lot's of scope within these principles for some fascinating innovation.  

* All the stover is left on the surface of the soil.  Stover is all the parts of the plant that are not utilized by us.  If you have planted corn, stover includes all the stalks, leaves and if it is possible, the cobs.  If you chop it up while harvesting, so much the better.

* Stop plowing.  It disrupts the funguses which are the farmer's little helpers.  If you plow a field regularly, you will be hard pressed to find a worm in the soil.  If that isn't an indication of a sick field, I don't know what is.  If you have to seed the field, either use direct drilling or open a small trench of the desired depth and drop the seeds into it.  

*Never leave the soil bare.  Plant a cover crop.  Legumes are a great choice as they fix mega-bucks worth of N into the soil.  All farmers have heard of N-P-K (Nitrogen, Phosphorous Potassium).  It is not accidental that they are in this order.  N is the nutrient needed in the greatest quantities by plants.  And it doesn't have to be a sacrifice crop.  Plant soy beans, alfalfa or other cash crops that fix nitrogen from the air into the soil.  Nothing new here.  Thousands of years before the chemistry/biology  was known, farmers knew to do this.  We seem to have to relearn everything every generation.

*Rotate your crops in as random a schedule as possible, leaving as long as possible between the same crop.  Pests just can't stand this.

*If you are grazing, put the animals into a field at such a concentration that they graze down the sward in one day while trampling some of the plants into the ground and defecating and urinating on the field and then move them to a new place.  You probably have to use electric fences for this due to the cost of permanent fencing.  Let the plants recover before putting the grazers back on to the area but don't allow the plants to go senescent.  Over-grazing and under-grazing are equally detrimental.

*Don't be bashful about putting chemical nutrients on your fields.  If a soil analysis shows that you are missing, for instance, Zn, Co, Se, Cu or whatever, apply it.  You can't grow healthy animals without the necessary macro and micro-nutrients.  Regenerative farming isn't some sort of religion.  It is farming with smarts as much as possible, replacing un-needed, costly inputs.  Oh! and when you get a soil analysis, get Total X rather than Available X done.  Once you have a vibrant rhizosphere# plus all the other wee beasties in the soil, they will mobilize what is in the soil.  You achieve this beatific situation by not plowing and by applying lots of organic material on the surface of your soil to power the soil ecology.

# funguses

Some interesting books

  By David R Montgomery

Dirt

The Second Half of Nature

Growing a Revolution

What Your Food Ate

 By Michael Pollan

The Omnivore's Dilemma

Monday, October 3, 2022

Omega 3 and 6 Fatty Acids

This is a book review of a small part of a book, What Your Food Ate, by David R Montgomery and Anne Bikle.  It is the most recent (2022) in a series of books including:

Dirt - what happens to a civilization that treats its soil like dirt

The Second Half of Nature - what goes on in a rich organic soil

Growing a Revolution - how to restore degraded soil in one to three years - a process that nature would take centuries to restore, working from the bottom up.

 

This essay on fatty acids is only a very small part of the book which is jammed packed with information on the food-value of foods grown in rich organic soil, compared with foods grown in degraded soils, using chemical nutrients.  The difference is significant.  So what is a fatty acid. 


A fatty acid is a chain of carbon atoms with three hydrogen atoms attached to one end and a COOH at the other end.  All the other carbon atoms in the chain have 2 hydrogen atoms attached to it.  An omega three fatty acid has one H atom missing from the third carbon from the three hydrogen end.  And as you might guess an Omega 6 fatty acid has one H atom missing from the 6th carbon atom from the three hydrogen end. 


Both types of fatty acid are necessary for human health.  The Omega6 fatty acid play a role in inducing inflammation.  Inflammation is part of the defense of the body against viral and bacterial invaders.  Omega 3 fatty acids play a role in shutting down the inflammation when it is no longer needed.  The ideal ratio of these fatty acids in the body is 1:1.  If there is an excess of Omega6s, inflammation may carry on and this can lead to auto-immune conditions and even cancers.  


Humans and many animals can not manufacture these fatty acids.  The ratio in your body reflects the ratio in the food you eat.  This is the same for livestock and if you eat meat that has a 1:1 ratio, you will tend toward a 1:1 ratio*.  

*Of course you don't only eat, say, beef.  The rest of your diet contributes to your 3-6 ratio.

 

The milk, butter and cheese of a dairy cow will also reflect the 3-6 ratio in the feed of the cow.  

 

Cattle that eat pasture plants will have the ideal 1:1 ratio of fatty acids in their meat.  Cattle that eat concentrate, especially concentrate that is heavily based on corn, will have highly excessive Omega 6 fatty acids in their meat.  If a cow has been raised all her life on pasture and then 'finished' in a feed lot, it only takes a month or two for her fatty acid ratio to reflect her new feed.

 

You see where we are going with this.  I always thought that the "Pasture Fed" advertising was just a marketing gimmick.   Apparently not.  It really is far better to eat pasture fed meat than feed lot meat.  I suppose the same would apply to hunted deer, pigs, birds in comparison to the same animals,  raised on concentrate. One wonders if feed lots explains the preponderance of auto-immune type conditions that seem to be increasing just as we have pretty well conquered diseases caused by micro-organisms. 

I would heartily recommend getting the four books mentioned at the start.  They explain so much.  By the way, there are no references in What Your Food Ate.  Including them would have increased the size of the book by 50 pages so the authors put the references on line.  The URL, if you want to have a look at them is www.dig2grow.com 


There is much more information on fatty acids in What Your Food Ate and on the nutrient quality of food grown on rich organic soil vs food grown on degraded soil with the nutrients provided from chemical fertilizer.  In a sentence, the concentrations of minerals, vitamins and phytochemicals in plants grown in rich organic soil are considerably higher.               

Sunday, October 2, 2022

My Nissan Leaf

I love my Leaf.  I have never been a petrol-head, even as a teenager.  I just wanted a car to get me from A to B (and of course with my girl friend by my side).  But my electric Leaf is something else again.  I'm a very conservative driver and drive gently but when I want to get out into traffic or pass someone with limited space to do it, man! does my Leaf get up and go.  It's a real jack rabbit.  I can understand why some electric car owners have to change their tires more often than when they drove and ICE car.  

And while we are at it, let's look at the cost of driving compared to an ICE car.  My Leaf has a range of 300km (actually more like 350 but let's keep the numbers simple) with a 60kWh battery.  Dividing 300 by 60, we see that I can drive 5km per kWh or for the sake of comparison, 10km per kWh.  Now here a kWh cost me 25c so I pay 50c per 10km.  (actually I have solar panels but that is another story).  

A similar size ICE car gets about 10km per liter of fuel.  Here a liter of fuel costs $2.50.  Ergo, it costs me a fifth as much on electricity than it would on fossil fuel.  Add to that, that I hardly ever use my brakes and have no oil to change.  On the other side, I think I may need a new set of tires more often with my Leaf.

I think the Leaf could become the iconic  car of this century.  That is if they changed their business model.  For me, at least, their car is excellent and is all the car I will ever need or want but their business model doesn't put the customer first.

For instance, if you have one of the early 24kWh (kilowatt hour) batteries, the battery is probably getting a little tired by now and you won't have the range you once had.  If you can fine a wrecked Leaf with a 24, 30 or 40kWh* battery, it is a matter of about an hour's work to change out your battery for the one in the wrecked Leaf.  Suddenly the range of your Leaf has jumped way up.  And the chemistry back then was not what it is now.  Your new (used) battery is likely to last  longer than the original.  

*A 60kWh battery is apparently a real hassle to fit to the earlier models.  Possible but Quite difficult.

But the Nissan company doesn't make it easy to buy a new, higher capacity battery for your Leaf.  In fact, at least here in New Zealand it is virtually impossible.  This is not a company thinking of the best interests of her customers.

My second gripe is about the temperature control of the battery.  Apparently, too high or too low temperatures are bad for the battery and cause the battery to degrade more quickly.  Nissan should start to put temperature control around her batteries.

So what could Nissan do, even now, 22 years into this century, to make her car the iconic one instead of Tesla.  Actually, she would only make the Leaf iconic for one portion of the market but I suspect this is a huge percent of the market.  There will always be people who want the latest with all the bells and whistles.  Here is Nissan's advantage.  A whole bunch of us don't want this.  We want a reasonable looking car with very good range, ease of repair, nice handling but most of all a low price tag.  How does Nissan achieve this and still make a great profit.

1/  Keep the leaf the same from now on.  The only innovations should be ones that make the car cheaper or with better battery chemistry.  

2/ Decrease the cost of manufacture by, for instance, adopting Elon's mega-casting machines.  With the way you have your battery in the Leaf, you might be able to cast the whole chassis in one go, unlike Tesla that does it in two parts.  And while you are at it, make the underneath of the car flat.  At the back is a hollow that probably held the spare tire when they used the frame from one of their ICE cars for the Leaf.  If the bottom of the car was flattened out, there would be a huge increase in the trunk space.  An added advantage is that apparently a flat under side of a car improves its streamlining.

3/ Keep all the controls tactile.  No touch screens.  The radio in my Leaf is great.  It has a knob on the left for tuning and one on the right for volume and turning on.  Also there are volume control buttons on the steering wheel.  I never have to take my eyes off the road to operate my radio.  All controls should be similarly tactile.

4/ Produce a van for the 'tradie', the plummer, electrician, builder and so forth.  Provide a 220V AC outlet that the tradie could use and lots of attachment points inside the van for attaching shelves and things.  Make it with two sliding doors. Adopt every bit of kit possible from the Leaf.  Only innovate when necessary for the function of a van.

Monday, September 26, 2022

Autumn melt spikes on Greenland

I'll go out on a limb and make a prediction.  The Autumn melt spike on Greenland that we saw this year (End of September 2022) will become the normal situation as the years go by.   So what is the reasoning behind this prediction.

 

First let's look at the normal (usual up till now) situation with the Hadley Cells.  The equatorial Hadley cell is powered by the heating of land and sea around the equator.  Let's keep it simple and ignore various finer grained effects involving, for instance latent heat.  The air is heated from below by the warm surface of the earth, rises and flows North and South at altitude.

 

The Polar Hadley cell is powered by the air   radiating heat into space, becoming dense and sinking.  It is not heated from below because the snow and ice over the Arctic Ocean reflects most of the radiation falling on it back into space.  Besides, much of the year, in winter, there is virtually no radiation falling on the land, and ice covered sea.

 Hadley circulation

Consider for a moment what would happen if these two cells met at 45 degrees North (Let's ignore the Southern Hemisphere for now).  Air at 45 degrees north is trying to both rise and fall with the Arctic Hadly cell air warming as it flows southward and 'wanting' to rise.  Air from the Equatorial Hadley cell, flowing northward at altitude cools by radiation and wants to descend,  Instead what happens is a third cell, the Ferrel cell is induced.  

 

This third cell,  the Ferrel Cell  acts like an idler wheel in an engine (the one that keeps your fan belt tight, for instance) ((if you are still driving an ICE dinosaur))


Incidentally, jet streams occur, at altitude, where Hadley cells meet

 

Now we throw a spanner in the works.

 

We add greenhouse gasses to the atmosphere and this results in the melting of more and more floating ice on the Arctic Ocean.  Radiation that falls on this open water over the summer penetrates the water and is absorbed, heating the water.  This results in more melting ice and more heat absorption.  The sensible heat of water is high (one Calorie* per kg of water) and the heating is over a considerable depth so a lot of heat is absorbed with a modest increase in temperature.  

*A large Calorie as opposed to a small calorie (which will heat one gram of water one degree C).

 

In the mean time, the land is heating up.  The land only heats up at the surface;  say a foot in depth or so and the sensible heat of land is less than water so the same amount of heat will raise the temperature of land more than water.  It can become quite hot on land, in the Arctic, in summer.  This induces an onshore wind.  The air over the ice-covered ocean is cold and flows toward the land which is warm.  (Air rising, over land, sucking air from the ocean)  With Coriolis, you have the polar Nor-Easterlies (Air flowing toward the South West).  So now we get to what is likely to happen in the fall.

  

The land has warmed much more than the ocean, but not absorbed much heat and it cools off quickly as solar radiation decreases.  Not so the sea and the  open water that increases year by year.  It cools more slowly.  In addition, when it cools enough to freeze, it gives off latent heat of crystallization which slows the cooling.  The effect I'm talking about, namely autumn melting spikes, will occur more and more as we see increased open water during the summer.

 

With the land around the Arctic cold and the ocean still relatively (to the land) warm, you should have off-shore winds.  In fact you may even induce a 4 Hadley cell system for a while*.  And when the Arctic really gains power due to much more open ocean, holding much more heat, eventually, you should actually suck the whole system northward and have a two Hadley cell system.  A good indication that we have reached this situation will be when the  Polar Jet Stream disappears.  Jet streams occur where Hadley cells meet.  So now, how about Green land melting.

* Since jet streams occur where Hadley cells meet, you might even observe an extra jet stream for a short time.

 

Air flowing off the land will be warming and becoming humid as it flows across an ever more open ocean and will tend to form counter-clockwise systems due to Coriolis.  This warm moist air will impinge on Greenland where not only will there be rain but a kg of moisture condensing out of the air onto the ice, releases enough heat to melt 5 or 6 kg of ice*.  (For water the latent heat of evaporation/condensing is 6 times as much as the latent heat of melting/crystallization).  Another couple of effects may come into play here.

* Heat of crystallization/melting is 80Cal per kg.  Heat of evaporation/condensation is 540Cal per kg.

 

If one of these low pressure area sidles up to the West coast of Greenland, on its northern side it will be sucking air down the slope and on the southern side pushing air up the slope.  Lets look at the North side.  When air flows down a slope, it heats up by 9.8 degrees C per km fall.  This warming air will melt ice if it reaches and exceeds 0 degrees C.

 

On the Southern side it is pushing humid air up the slope and, depending on exact conditions, may be causing rain which melts the ice.  And if the humidity in the air flow is condensing on the ice, it will be melting ice due to the latent heat effect described above. 

 

There is another possibility.  If the air is simply flowing toward Greenland, (atmospheric river?) it will come into contact with the ice and condense, causing melting as described above.  This will make the air dense and it may be full of droplets of water (fog) making it effectively even more dense and it will flow down slope to the sea.  We have the adiabatic melting effect described above, and may form sort of a miniature Walker cell between the ice and the sea.  Convective processes are much more effective at transferring heat than conductive or radiative effects and this could melt the ice at a shocking rate. Essentially, heat is being transferred to the ocean from the huge store accumulated all summer in the ocean .

(Read Plains of Passage, by Jean Auel - chapter 41 or so.  The book is a novel but Jean did her homework and described what happens when Foen winds occur over ice),  The resulting Peteraqs are intense.  Classic Peteraqs are typically well below 0 degrees but the atmosphere is warming.  Imagine one of these density winds that is above the freezing point, blasting across the ice.


Then, if all that wasn't enough, there are storms that come up the East coast of North America.  If the water they flow over is cold, they loose their umph but as the water becomes ever warmer, they can travel further North.  We have another mechanism for putting a storm up against Greenland with the same results as above.

 

Even a high pressure area sitting beside Greenland can do the same as long as the winds it creates are blowing across a warm ocean.

 

If these storms sidle up to the East coast, the same as above applies except the rain will be induced at the northern edge and the adiabatic melting at the southern edge of the storm.

 

So in conclusion, I think it is quite likely that we will see melting spikes in the fall just like the one this year.   They will occur in years in which the sea has accumulated a lot of heat and will happen as the land cools off, resulting in a strong pressure gradient from the land to the sea.  The strength of off-shore winds around the Arctic Ocean will signal the start of this process and how strong the melting is likely to be in any year. As the sea freezes over, and especially  if it acquires an insulating layer of snow, the process will stop. Initially we may  see a short-lived, extra jet stream but eventually as the Arctic ocean gains power, the northern-most jet stream will likely disappear in the fall.


Tuesday, September 6, 2022

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.