A Climate Hypothesis

[ecosophia]

I find myself in the rather odd situation of having come up with a detailed and, I think, unique hypothesis about where the current round of climate change is headed. As far as I know it works in terms of physical laws, and the global climate seems to be shifting in the direction I'm anticipating, but as far as I know I don't have any readers who are climatologists and thus can check my work -- and the academic scene isn't exactly enthusiastic about outsiders proposing theories. 

Here's the hypothesis. Right now the climate of each hemisphere of the earth is dominated by three circulations of air -- cells, in climatological jargon. The whole shebang is driven by the temperature difference between the tropics and the poles. The tropics get all that sunlight pouring straight down from above, so heated air tends to rise along the equator (more exactly, the ITCZ or intertropical convergence zone, but we can be schematic for the moment). That produces the Hadley cells shown on the left: warm air rises to the edge of the stratosphere, flows poleward at high levels, then sinks back down around 30° of latitude. It's bone dry by then, which is why there's a band of desert around the globe near 30° north and south. Then the air gets drawn back toward the equator, sucks up heat and moisture, releases the water as it rises, and the cycle continues. 

You get a similar process at the poles, but here it's driven mostly by the intense cold at the poles themselves. That causes air to sink, and sets the polar cells in motion. That's why the arctic and antarctic regions are quite literally deserts -- the air that sinks and then flows out from the poles is bone dry as well as very cold, forming the bleak arctic and antarctic easterlies. 

Between them is a third set of cells, the Ferrel cells, which are weak and unstable. Some air that's sucked upwards around 60° nortth and south latitude goes toward the equator rather than back to the poles, some air that comes rushing down around 30° latitude flows toward the poles instead of back to the equator, and the instabilities give the temperate zones the unstable weather we all know so well. 

Got it? Now factor in greenhouse gases. Those, in effect, increase the insulating value of the atmosphere and thus make the transfer of heat from the tropics to the poles more efficient. The increasing heat in the arctic region melts the sea ice: on the right is a useful chart of the decline in ice cover. 

Ice reflects sunlight -- in technical language, it has a high albedo. That means that most of the heat that falls on the Arctic Ocean gets bounced straight back into space to warm the cockles of alien species on worlds orbiting the circumpolar stars. Open water has a much lower albedo -- when sunlight falls on it, the water soaks up heat. Water's really good as a heat sink, so it takes a lot of sunlight on open water to warm the sea -- but the Arctic Ocean's got a secret weapon. All summer, the sun stays above the horizon 24 hours a day. So as the ice goes away, the Arctic Ocean warms...

...and once it passes a certain threshold, which I don't have the math skills to calculate, the Arctic Ocean becomes warmer than the land areas immediately around it. That's especially true in winter, when balmy regions such as Siberia and Greenland would be a lot colder than an unfrozen Arctic Ocean. 

That, in turn, would cause the collapse of the polar cell. Remember that what keeps those dry frigid easterlies blowing in the arctic is the intense cold of the polar regions. Once the Arctic Ocean is ice free, it's warmer than its surrounding area, and so you don't get cold air dropping down from the upper edge of the troposphere -- you get temperate, moist air sucked into the polar area, where it rises, dumping heat and precipitation as it goes. 

The most likely result, based on everything I know about thermal circulation, is that northern edge of the Ferrel cell in the northern hemisphere shifts north so that the rising zone now at 60° north is around the north pole, the northern edge of the Hadley cell in the northern hemisphere moves northwards accordingly to around 45° north...



...and climate belts shift spectacularly.  The red line above is 45 degrees north, halfway between the equator and the north pole. If my hypothesis is correct, this will be the new location of the global belt of deserts in the northern hemisphere, because that's where the dry air from the upper troposphere spilling out from the ITCZ will come rushing down, the way it now does over the Sahara desert and similarly verdant regions. Well south of that line, you'll have savanna, and well north of that -- say, in what's now Alaska and Siberia -- you'll have the kind of temperate climate we now get around 45° north. 

There are a couple of points worth noting here. First, 10,000 years ago this is pretty much what the climate of the northern hemisphere seems to have looked like. At that time the Sahara was a vast stretch of savanna, watered by annual monsoons off the Indian Ocean and inhabited by elephants, lions, and human beings. Back a hundred millennia or so, in the Eemian period between the last ice age and the one before it, the same seems to have been true also -- at that time there were hippopotami basking on the banks of the Rhine and the Thames. (Their fossils have been found.) 

Second, there's some reason to think the collapse of the north polar cell and the northward shift of the Hadley and Ferrel cells may be happening already. Here's an article from Nature talking about the baffling northward shift of the tropical zone; here's an article from Journal of Geophysical Research arguing that a partial collapse of the northern polar cell actually took place in the 1980s. This is just what I found with a fast internet search; I'm sure someone with the necessary background could find much more relating to this suggestion. 

Third, the change may not be gradual. The atmosphere, like many complex systems, tends to shift suddenly from one relatively stable condition to another. Paleoclimatic evidence suggests that changes in climate belts and temperature patterns in the prehistoric past took place very quickly in at least some cases -- we're talking here a matter of a few decades at most. Climate is strongly affected by mountain ranges and the distribution of land and sea, of course, which is why there isn't a nice even belt of desert around the world at 30° north and south, but the rapid desertification of the American west and some of the other climate changes currently under way may turn out to be harbingers of future climates for which most people, and most governments, are hopelessly unprepared. 

So there's my hypothesis. I'd be very interested to hear from anyone who has the necessary technical knowledge to comment on it -- and of course to field questions and comments from readers more generally. 

Comments

[francis_tucker]

If your hypothesis is true, does this change your earlier prediction that the Great Lakes region will be the optimal place to live in the Lower Forty-Eight once the biggest part of the catabolic collapse rubble has finished its most violent bouncing?

[ecosophia]

That's a very good question to which I don't yet have an answer. I need to find out a lot more about the paleoclimates of North America!

[(Anonymous)]

There's a positive feedback loop I'm watching which could prompt some very quick changes in the very near future: as you mentioned, the melting ice sheets are reducing the albedo of the area. The catch though is that the ice has had several centuries to build up to its current level, and so the ice is quite thick in some places, especially near the pole. What this means is that much of the energy being absorbed by the arctic, especially near the pole itself, is currently going into reducing the thickness of the ice sheet, in addition to shrinking it in terms of area.

Each year a little more melts, and what's left is both a little smaller and a little thinner; and these effects both mean that next year, the winter build up would, even ignoring that it's a little less each year as well, replace less and less of the ice; with the effect being greater than what is obvious merely from looking at the decline in ice area.

At some point, and I think there's a good case for saying we're either there already or getting quite close, there's not enough thick ice left for the sea ice to be stable, and what happens next is a rapid change, since what's left can come undone quite quickly in the summer, and then the ice free Arctic Ocean sucks up heat and thus there's a dramatic reduction in how much ice coverage forms in the next winter.

Add to this that melting all that ice absorbs a lot of heat (water has a very high specific heat of melting, to use the technical term), and once the Arctic Ocean is ice free all that heat which currently goes into melting the ice will go into warming the ocean; and this means that once that happens the pace the ocean warms is going to shoot up like a rocket.

[ecosophia]

Yes, and that's one of the things I'm watching. Even so, the Arctic Ocean is going to have to soak up a lot of additional heat before it remains blue water year-round. The difficulty is, again, that I don't have the math skills to figure out how soon that's likely to happen.

[jprussell]

Thank you very much for sharing this! I do not have the technical know-how to offer informed commentary, but it's a topic I've been very interested in.

If I might ask a couple of clarifying questions:

1) I've read some stuff talking about the political influences on the scientific publications about climate science. I know that you are excellent about noticing these kinds of distortions to the scientific process, so I wonder if you might share a bit about how you've approached deciding which studies to take seriously and which to treat more suspiciously?

2) Somewhat linked to the above, I've also read assertions that much of the data on paleoclimatology is too small and/or specific to generalize from. Often this assertion is mashed up with political claims as with 1) (for example, the idea that much of the "global" temperature data cited by climate scientists has been cherry picked to support a dire view of what's happening). Further complicating things, these claims are usually made by folks of a contrarian political bent (like Eric S. Raymond and Curtis Yarvin), which makes it even harder to decide if they are making accurate, but unpopular-in-the-mainstream claims, or if they just have their own political axes to grind. All of which is a quite long set up for an actual question: as a non-specialist who well recognizes many of the distorting forces in mainstream modern science, what have you looked for to take studies seriously and trust that they are as generalizable as they claim to be?

Thanks very much again for putting this forward clearly and concisely,
Jeff

[ecosophia]

1) I focus on data rather than predictions, and on data that can be matched with real-world confirmations. For example, the fact that marine freight is now going from Asia to Europe along the northern coast of Russia every summer shows conclusively that sea ice is in fact much less widespread than it was a century ago.

2) The thing Yarvin et al. don't seem to have noticed is that paleoclimatology does not justify apocalyptic predictions. The Earth has been much, much warmer than it is today -- that's easy to demonstrate from geological traces -- and it's also had much more CO2 in the atmosphere than it does now -- again, there are plenty of good proxy measurements. It's precisely because paleoclimatology doesn't justify the current narrative, except in narrow, cherrypicked cases, that I take it seriously. As a rule, look for data that doesn't fit the narrative and you can be more confident in it.

[ecosophian]

I know nothing of climate science, but two thoughts:

1. The first image looks a lot like an astrological birth chart.

2. Depending on the time of this happening, it might be a good idea to move to Alaska.

[ecosophia]

1) I suppose it does!

2) Depends on what kind of climate you like. I'm pretty sure, given the change in wind and weather patterns, that New England is going to end up with a rather pleasant climate, toward the Mediterranean end of the spectrum.

[deborah_bender]

I'm not qualified to critique your theory. I'll just observe that ocean currents also have a strong effect on climate.

Latitude 45 in Europe has a warmer and milder climate than latitude 45 in North America. The first English colonists were unprepared for the severe winters.

As you have remarked, Europe is a peninsula of Asia. Every part of it is closer to an ocean or a large sea than the inland areas of the North America continent north of Mexico (I'm allowing for the distortion of the Mercator projection and the Great Lakes). This has a moderating effect on coastal regions.

You're perfectly aware of this, and probably expect to talk about it in the comments section. I have no predictions except to say that rising carbon dioxide levels might be more extreme or at least different west of the Atlantic than east of it.

[ecosophia]

Yes, those are also important factors. The hypothesis I've brought up only defines one set of variables, and there are many others. That said, there's evidence that oceanic currents are slowing down, and a blue-water Arctic would slow them much further, since here again you wouldn't have the same drastic temperature difference between equatorial and arctic waters.

[hippieviking]

I remember being young and feeling frustrated that the world was just so d@!m boring, why couldn't I have lived in a more interesting time?

I can't shake the feeling that things are on the verge of getting pretty sporty.

Of course, now that I have young children dependent on me for their safety and well being and I'm feeling slower and the aches and pains keep racking up, I'm not so hot on things getting more exciting...

I'd hope you were wrong on this count but, this all jives with my empirical experience as of the last decade or so.

I used to work for the feds in resource management. I talked with numerous peers about their experiences of extreme rain events and visited a number of sites. We would always attach a q value to a particular rain event. "At this location, it was a q2500...". In layman's terms this generally gets relayed as a 1 in 2500 year flood event, but really it means this sort of event has a 1 in 2500 probability of happening in any given year.

These events were always "anomalous". It was an outlier! But, the thing is, when you start to see extreme outliers every year or couple of years... they cease to be outliers, don't they?

I keep thinking about the old "may you live in interesting times".

HV

[ecosophia]

I know the feeling. ;-)

What about the south?

[sea_spray]

Hi JMG

Being currently at 43 degrees south this struck a cord. I suppose that the same thing may play out in the southern hemisphere. Though the differences that stand out are that the east antarctic ice sheet is rather more stable and there is a land mass there once the ice is gone.

To speculate on that will happen here in New Zealand where I am: I looked at Paleo-climatic studies which found based on pollen cores that the climate of north and south end of the country ended up similar to what the north end is now. At the moment the north end is sub tropical with avocados growing.

It seems reasonable to suspect it may reflect present day southern japan because it's on the western edge of the pacific ocean and at 30 degrees north.

Being an island I would expect the local weather systems to be able to bring in rain, just as Florida and South East Asia receive now at 30 degrees north, although possibly in a monsoonal pattern. At least I hope so.

Sea Spray

Re: What about the south?

[ecosophia]

The southern hemisphere faces a rather different situation, because you don't have an ice-covered ocean at the south pole, you've got a continent with a mile or two of ice heaped on top of it. I'd expect heat transfer to the south pole to pick up, too, but it's got much more ice to melt first. It's quite possible, in other words, that for some thousands of years the two hemispheres will have different atmospheric circulations. That said, your paleoclimatology is likely to be a good indicator of what you'll get.

[weilong]

I'm just an amateur meteorologist, but I have studied the subject. I see a few points that might need some work.

Land heats up faster than water, and also cools faster. Water, maintains a much more stable temperature both diurnally and annually. The origin of the sea breeze, for example, is because the land heats up quickly while the sun is shining on it; it becomes warmer than the sea during the daytime, causing the air over it to rise and sucking in air (i.e. wind) from the relatively cooler sea. After the sun goes down, the land cools quickly, and when it becomes cooler than the sea, the wind reverses and blows out to sea. Similarly, high pressure areas (where air is descending and then blowing outward when it hits the ground) tend to develop over continents in the winter, because the land is relatively cooler than the oceans. The opposite happens in the summer, when relatively warmer temperatures on land cause low pressure systems to develop over the continents.

I don't really know enough to be able to say what will happen as arctic sea ice diminishes. Presumably there is an interplay between the albedo of the land (also covered with snow for part of the year) and that of the sea. As mentioned, the arctic ocean also has some heat exchange with more southerly bodies of water. As for what happens in temperate climates, though, it is as I described above: bodies of air descending over the land in the winter, and the reverse situation in the summer. Just a guess, but since the arctic ocean is surrounded by land, I would say that the polar cell circulation might be reinforced by a ring of warm land around a relatively cooler ocean during the arctic summer; and a possible tendency to reverse in an ice-free arctic ocean during the winter.

[ecosophia]

Thank you for these -- all points that would need to be considered in a more detailed formulation of the hypothesis.

[(Anonymous)]

Thanks JMG, I was mulling on this based on some hints you dropped some time ago. I had little success in finding any good articles about what to expect moving forward - plenty of models but no simple mental models based on analogies with the past.

I am not a climatologist but I do have a couple of observations:
- First, just a nitpick. You mention decline in ice cover but the graph is about ice volume, which is actually much more interesting (and scary).
- This page from ORNL (https://www.esd.ornl.gov/projects/qen/nercNORTHAMERICA.html) mentions that there are few data point for Eemian. I wonder why? It is a very recent period. I would think the climate scientists would love to study a recent warm period to help understand where we're going!
- A google search for "eemian" returns this old article (https://phys.org/news/2012-06-climate-cold-arctic-eemian.html) as first result. Apparently, the Polar ocean behaved differently so the Eemian is not a good analogue for the current climate change episode.

I did mention in the main blog that I don't look into AGW much anymore because I hate the manipulation of data for political purposes, or just to steal money.

But this quick search left me wondering - is there any honest science left? Why aren't people looking for data points for Eemian? Why is a 10 year old article the first answer in google? Why do climatologists love computer models but not historical comparisons?

So thanks for this hypothesis and please let us know of any interesting articles you might find.

NomadicBeer

[(Anonymous)]

The problem is that once you start to start things like the Eemian, you quickly come face to face with a very awkward reality: a warm climate is nothing like the tepid one we have now. Faced with the realities, a lot of people find various ways to wig out. This is especially the case since right now there's only one obvious reason the Eemian would be any different than today: the Eemian had time to settle into a stable state.

Given we've only recently passed the concentrations of CO2 seen in the Eemian, it makes sense that our climate would still be different: we have a lot of ice to melt...

taking a swing here....

[drhooves]

Excellent hypothesis.

It's been a while, but in my Air Force days I worked for a couple of years on climatological analyses, though they were more aviation and military oriented, like calculating stats on the best time of year to launch testing rockets from Wallops Island, and the exhaustive statistics related to the first 25 shuttle launches after the Challenger disaster. So, not paleo-climatology, but I do recall a few things related to your post.

The changing climate is definitely reflected by the changes in atmospheric circulation, and the migrations of the desert belts as you've suggested seems quite reasonable. The key take away is the rate of change can be much quicker than is usually brought up when climate change is discussed. The climate could "break", just like someone going broke, slowly and then all at once, when critical thresholds are exceeded. What those are, from what I can tell, are not very well understood.

I don't recall spending a lot of time studying the polar, Hadley and Ferrel cells, as that doesn't come into play much for meteorology, but what you've described is perfectly sound. What I do recall from climate and oceanography classes is the "transfer belts" of the ocean currents, and I believe they are responsible for the majority of heat transfer between the tropics and the poles. Ocean currents are influenced by winds, topography and the Coriolis affect among other factors, so I guess an argument can be made on cause/effect or chicken/egg as to what is the dominant process - wind or water. The vast amounts of energy involved and the slight changes over time that affect the balances of climate are very complex.

You mentioned topography, which is also very key to climate - put a 6,000 foot mountain range along the Gulf Coast and where I live (downstate Illinois) can maybe grow a few weeds, but not the mountains of corn and soybeans that 45-50 inches of annual precip allows. Another key point is the amount of water vs the polar and mountain ice caps, as the albedo of water is like laying a black plastic cover over a swimming pool in the summer. Because water has such tremendous latent heat capacity, it takes a very long time for changes to occur that affect climate - but once tipping points are reached, the delicate balance of ocean temps, ice cover, prevailing winds, and weather patterns can all change dramatically - and quickly.

I'm not up to speed on the added effect of greenhouse gases. CO2 gets all the press, but its cumulative effect doesn't change much past 250 PPM or so, I believe. Methane of course is a beast, and if some of the calculations on frozen deposits are correct, we'll be in big trouble soon. Some of the gases introduced by our species as non-natural greenhouse gases are still in small quantities, but certainly aren't helping. Pollution and running out of fossil fuels are problems that are beyond debate.

The 2004 movie The Day After Tomorrow had scenes early in the movie about ocean buoys reporting abnormally cold temperatures, followed by the earth going into an ice age in less than a month, IIRC. Probably a little on the extreme end of the short time scale, but a dramatic shift in climate even over a few decades is going to result in big problems. The logistics in trying to mitigate rising or falling oceans, the shift in rain belts and deserts, the migration of people, etc., is just mind boggling. And it's not like we don't already have enough challenges, even if the climate remained perfectly stable for the next few hundred years....

Re: taking a swing here....

[ecosophia]

Thanks for this. The idea of an instant ice age was popular back in the late 1970s, too -- I recall a lively if somewhat trashy SF novel, The Sixth Winter, that had that theme. (It was one of a bumper crop of ice age-themed SF, from the days when climatologists thought we were headed for an ice age. That said, a more realistic shift of the kind that unfolds over decades -- yeah, it's going to be a major crisis.

stability

[(Anonymous)]

Disclaimer: I'm a layman in this field.

Intuitively, going from three to two zones could result in that 45 degree boundary being very unstable. As things are, the boundary between the zones isn't a nice neat ring, but for example the jet stream winds and snakes chaotically. When it's very weak, it can coil into strange patterns like the one that resulted in the mild, drizzly summer in the American midwest in (IIRC) 2013. Two zones sounds like a recipe for long, slow, and severe oscillations at the border. And, indeed, relief from recent droughts in the American plains and mountain seems to come in floods (not sure if the data supports that).

Also, there is the question of how ocean currents would change, which seems like an even more complex phenomenon.

John N.

Re: stability

[ecosophia]

I could definitely see an unstable boundary between the two cells, and that would make things very weird in the middle latitudes. As for ocean currents, no question, that's another huge issue -- a shutdown of the deepwater circulation followed by deepwater anoxic conditions over much of the world's oceans seems likely to me, but that's a whole 'nother can of worms.

Amateur ramblings

[vitranc]

Hi JMG,

This had me thinking, and there are some of my thoughts on this topic.

1. “Shrinking is not linear” The collapse of the polar cell would by itself be a process. Therefore, now we are supposed to see the shifting tropical regions due to weakening of the polar cell. The cell contracts and the other two cells expand accordingly. But this would not go on like this indefinitely. There would not be a linear function until the polar cell encompasses 1 degree and the other two are 44,5 degrees each. At one point it collapses. But…
2. “The reordering as a characteristic” Even this collapse and reestablishment is not enough. Such processes have a characteristic. So Let’s assume the process reaches the terminal point for the collapse of the polar cell. Does it then have enough heat to go in reverse immediately, or does it take decades of chaos, before the polar regions build up enough heat to start the thermal engine in reverse.
2. b “addendum” On review; it might really be a characteristic, and the circulation runs in one direction so long as the temperature of the polar ocean does not reach the temperature to run the process in reverse. At that point it does shift abruptly, but it would mean a longer time until it collapses.
3. “The number of cells” your mention of crocodiles and hippocampi sunning on the banks of the Thames got me thinking. If the 45 degrees get the desert treatment due to the two cell model. This is improbable. Hippos do not live in the deserts, they live in the tropics. Plus the Nile may flow trough the desert and have hippos in it. But it feeds from the tropics. Where does the Thames get its precipitation in the case the British islands are dessert islands? But why would we get a 2 cell model? In the same line of thought, why do we not have a one cell system now. Air rises in the tropics and descends in the polar regions. Maybe the girth of the cells is limited. So could not the realignment become 4 cells? ~22,5 degrees each.

I must confess My knowledge about historical climate in the current temperate regions is lacking. But maybe my thoughts can help you.

Re: Amateur ramblings

[ecosophia]

Thank you for all of these. The hippos are more straightforward than that, however -- the 45° north line runs through the Alps, and so the lower Rhine and Thames are well north of the desert belt, in savanna territory, where hippos do very well.

Asteroid impacts 65,000,000 years later...

[(Anonymous)]

In other words, the Earth is still thawing out from the "beyond nuclear winter" from the asteroid strike that killed the dinosaurs. No real surprise there.

As far as greenhouse gases go, I remember reading somewhere recently that CO2 greenhouse effect actually saturates because there is only so much energy available at the 10.2 micron line for CO2 to absorb, and something like 90% of that energy is already absorbed at 100ppm CO2, which is well below current levels. Further, plants basically starve at 200ppm CO2, and grow much better with higher CO2 concentrations, enough that greenhouses often burn propane or other hydrocarbons specifically to increase the indoor CO2 level. I know JMG has no answer on this, but perhaps someone in the rest of the commentariat can either support or refute this?

At this point, I suspect that the academic climatologists are mostly frauds. Vast gatherings of private jets at climate conferences does not help that appearance. There's the problem of eventually depleting fossil fuels, but the one thing fossil fuels cannot do is cause a runaway greenhouse effect. This is simple stoichiometry and biology. All of the carbon bound up in fossil fuels was removed from the atmosphere using photosynthesis eons ago. Since all of that carbon came from the atmosphere, closing the carbon cycle and returning it to the atmosphere cannot cause a runaway greenhouse effect. If it could, that effect would have already happened, long before our species appeared on this planet.

This almost feels to me like some kind of Cult of Progress insanity, but I'm not quite sure how to outline it.

PS: You must be on some kind of right track to attract the ongoing attacks. CloudFlare is being extremely annoying to Tor Browser visitors who have JavaScript disabled. Other Dreamwidth blogs aren't currently affected.

Re: Asteroid impacts 65,000,000 years later...

[(Anonymous)]

Based on what I read, yes, the CO2 is not the most important greenhouse gas.
In fact, water vapor has that title.
So why don't we worry about water vapor? Because it's a dependent variable mostly.
But CO2 (or other GHGs) can act as a trigger, bringing more water vapor which raises the temperature, which brings more water vapor and so on...

Because climate involves many exponential cycles like the above, it's very hard to predict.

Another example: in previous warming periods, CO2 was a lagging indicator (based on ice core samples). So what triggered warming? Milankovich cycles mostly, but who knows.

The point I am trying to make is that this is a complex system so I don't believe when people are absolutely certain.
Climatologists have their models that they trust more than actual real-life data, and that's crazy.

But also, being certain that we cannot have a runaway greenhouse effect is just as crazy. For one thing, the Sun is emitting more radiation as time passes so the same amount of carbon causes more heating. The other aspect is that "hothouse Earth" (which happened before so obviously can happen again) might not be hospitable for large land mammals.

I don't worry about it though - it is small probability and not much I can do about it.

Southern Hemisphere

[(Anonymous)]

Greetings all!

Scary post really. Can we presume that a similar shift in cells will occur in the southern hemisphere then?

If your hypothesis is correct then we can expect massive blows to modern industrial civilisation. A few decades could mean as little as 10 years to 40 years. My guess is that options will be severely limited at best and at worse large tracts of land now populated will become empty. How to you prepare for that?

Karim

Re: Southern Hemisphere

[ecosophia]

1) The southern hemisphere will change much more slowly, because you've got Antarctica, with a miles-thick layer of ice that has to melt first.

2) That's an excellent question, which I haven't yet done the research to answer. Stay tuned!

10,000 years ago?

[(Anonymous)]

If I follow the argument here, which I could broadly sum up as “a change in the insulating value of the atmosphere causes a change in the position of atmospheric cells” - then the immediate questions are: why were the cells where they were at the Thames Hippo stage, and why did it then change to the situation we’ve seen more recently?

Re: 10,000 years ago?

[ecosophia]

Unfortunately atmospheric circulation doesn't leave fossil footprints! We have to use proxy measurements; the state of the Sahara is one. It was savanna from about 10,000 BC to about 4200 BC, so the latter may be when the three-cell system established itself.

Coriolis Effect

[(Anonymous)]

Huh, I thought the location of the cell boundaries was determined by the coriolis effect. With a certain planetary diameter and rotation then a certain number of atmospheric bands will form. A band could collapse due to a change of relative temperature, but then it would reform with a reversed vertical circulation.
-Social Scientist Way Out of His Knowledge Base-

Re: Coriolis Effect

[(Anonymous)]

I am not a specialist either but I know it's accepted as a possibility that Earth might have only one large cell during warm periods (see e.g. https://groups.seas.harvard.edu/climate/eli/research/equable/hadley.html)

[(Anonymous)]

Shouldn't and Ice Age be necessary first before this shift to occur?

[(Anonymous)]

What? Why would an ice age be needed for the arctic to melt?

And on the lower slope?

[australiandreamer]

Would that same effect be mirrored in the southern hemisphere (ie deserts pushing southward)?

(edit - just read the first linked article and the bulge is happening in both directions but they are suggesting different drivers for the north and south ... so the question is more whether your posited theory is applied to both halves)

Re: And on the lower slope?

[ecosophia]

Nope. Since you've got a continent at the south pole with a mile-thick blanket of ice on it, rather than an ocean with a thin skin of ice on it, the dynamics are different. Once the Antarctic ice sheets melt, it may be a different matter, but that's going to take a while.

[athaia]

I don't have any technical knowledge in that field - I just find it immensely amusing that this is exactly how I envisioned the climate zones in my post-apocalyptic fanfic. The placement of the desert belt is exactly where you put it.

One question: I read that as the northern ice cap melts, the resulting dumping of freshwater into the Atlantic Ocean would pretty much erase the North Atlantic Current, which means that the climate on the European peninsular would become colder and drier. Would that change be offset by the new placement of the Ferrel cells?

[ecosophia]

That's a fascinating question to which I don't yet know the answer. Since this is a very new hypothesis -- I literally thought of it for the first time yesterday afternoon -- there are plenty of questions like this that will need to be explored.

[(Anonymous)]

For what's it's worth, I remember reading some climate change prediction or other that basically boiled down to "everything south of the Alps is gonna be a desert".
That appears to be pretty much in line with yours, at least for Europe

Alpine

[cs2]

Uh-oh, I'm in the Alps. And here I thought we'd be good, with the mountains and fresh-water lakes, etc. (Those migrating from Africa are due for a bit of irony if the Sahara follows them north.)

[(Anonymous)]

Hi John,

Interesting hypothesis.

Presumably this process will take place over a space of centuries e.g. the desertification of southern Europe.

Further question, what will be the climate of northern Europe (places like the UK, Finland, Denmark and the most northern bits of France? Will that be in the desert or termperate region?

[ecosophia]

1) No, that's just it -- paleoclimatic evidence shows that climate changes of the sort we're discussing can take place in a matter of a few decades, as the climate shifts from one state to another. It would doubtless take a century or so for desert flora and fauna to establish themselves in southern Europe, just as it took around a century after the end of the Younger Dryas period for the Sahara to turn into savanna, but the crippling droughts could show up much sooner.

2) That's a complex question that will depend on local factors, but odds are that it'll end up with the kind of climate that southern Europe has now.

[(Anonymous)]

I'm wondering what happens to the ITCZ. Does it get really huge like a belly band of near constant storms, hazy skies, and light winds?

[ecosophia]

Somebody would have to run some computer models with lots of variables shifting this way and that to get some sense of how that would turn out. It's a fascinating question, however.

[(Anonymous)]

I'm in Nova Scotia, just south of the 45 degree line in the last map of the world in the post, and judging from recent news here, this post makes sense. The weather has been dry over the last three weeks, unusually so for May, and we have had two fairly large forest fires. Hopefully we will get a little rain tonight, but we could use a good soaking or two.

Right now, in areas along the eastern seaboards of continents in the northern hemisphere, those areas east of the dry spots are still pretty wet, like Florida. So if the Hadley cells northern boundary shifts north, then up here in the Maritimes could probably expect a Florida-like climate. Although that depends partly on what happens to the Gulf Stream as a result of climate change, and whatever the Pacific equivalent of the Gulf Stream is.

[ecosophia]

Thanks for the data points. I'm not at all sure how some of those details would play out, but you're right that the eastern coast of dry areas can be pretty wet -- Southeast Asia is another good example.

[booklover1973]

I think your hypothesis is plausible. Astronomers and climatologists who simulate the climate of Earth and other planets with changed parameters like, insolation, eccentricity of orbit, obliquity of the rotation axis, and length of day are coming up with quite a wild assortment of different climate states, involving, among others, situations where the atmospheric circulation of the simulated planet differs dramatically from current Earth.

A second factor which is relevant here is that in the further reaches of Earth's past, the climate was globally so warm and, compared to today, more uniform globally, that it is inconceivable that the atmospheric cell structure wasn't quit different from today.So, my take is that changes in the Hadley cell system not only is a plausible, but a probable event in the course of the climate shifts of the future.

[ecosophia]

Thanks for this. Yes, these are among the things I had in mind.

[booklover1973]

The fact that in several past epochs of Earth's history there were forests in polar regions (e. g. Antarctica during the early Tertiary) means that enough moisture for the growth of forests would have to be able to reach Greenland and Antarctica in the Paleocene and Eocene epochs; that means that the atmospheric and the oceanic circulation must have been different at these times.

[ecosophia]

Excellent -- yes, exactly. A Ferrel cell extending to the poles, and bringing moist temperate air from closer to the equator, would do that.