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.

 

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.

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.