Thursday, March 8, 2018

Water on the Rocks

Water on the Rocks


Many forms of thirst
How much fresh water would we need?
Why the poles?
Some Practical Problems
Tote that Berg!
Let's think bigger…
What is so special about towing?
What Sort of Vessel Should Convey the Payload?
Why ice?

Ice harvesting and Carbon Dioxide
Ice as fuel
Ice types and harvesting strategies
The big lumps
Deliver ice or water?
Why icebergs at all?
Why not make the ice instead of collecting it?
Why not pipe the ice instead of shipping it?
Brack, schmack!

Ice infrastructure, and commitment

Many forms of thirst

You should not see the desert simply as some faraway place of little rain.
There are many forms of thirst.
William Langewiesche, Sahara Unveiled

Many an old idea originally seen as impossible, unpractical, or stupidly cranky, has become first possible, then obvious, then vitally, routinely necessary. This has happened repeatedly throughout history and a good deal of prehistory, but as a trend it became especially obvious roughly at the time of the so-called industrial revolution. Significantly, the drive variously to ballyhoo or dismiss, disparage and destroy novel advances remains as compulsive as ever.

Nearly every genuine advance, whether based on old ideas or new, encounters greater difficulties than expected, but also becomes more valuable in more contexts than expected.

And some are more vital than expected.

The idea of exploiting the planet's largest resources of fresh water, namely our great ice sheets, has been bruited and mocked for perhaps a century, but though it repeatedly has been dismissed as stupidly unrealistic, the simple fact is that it is unavoidable. We will be doing it, like it or lump it, on a scale hardly imagined by either proponent or opponent. People will make and lose fortunes, people will die of it, and people will make livings from it as routinely as sailors sail and technicians build and tend wind turbines and high-tension lines.

For practical purposes this discussion ignores the harvesting of sea ice and glacial ice for the sake of luxury, fashion, science, or whim.  It deals with the older, more prosaic, more visionary, idea of harvesting utility or irrigation water in bulk, from sub-polar masses such as sea ice and icebergs.

As a serious suggestion the idea of iceberg corralling dates back to at least the first half of the 20th century, and it has met with understandable derision ever since.  Part of the reason was firstly, that the bulk requirement for water in those days was smaller and less globally urgent, particularly among populations that had the resources and skills to contemplate such giant projects. And most nations had nothing of the type.

Also, until recently the very idea of a major city running dry seemed ludicrous and therefore could be ignored; parched third-world villages were irrelevant because of their impotence.  They still look irrelevant, and still largely because of their impotence. The poor in their local drought-stricken valleys or villages we have had with us always and we see no prospect of their disappearing.

What is more, before the last twenty years or so of the 20th century the necessary technology for marine ice collection was not at a level that encouraged private enterprise to harvest ice for water; our shortcomings in the undeveloped technology still are something of a challenge. 

The very ideas that visionaries espoused, towing icebergs for example, genuinely were non-viable.  

Another reason has been, and still is, our lack of any currently adequate infrastructure; one does not go out on a whim to collect billions of tonnes of water and transport them thousands of kilometres, simply relying on the principle of "what could possibly go wrong?" The sheer scale of any viable project of that type beggars the imagination of Joe Average and Percy Politician, and so does the variety of obstacles to overcome; if so much as the thought is to be worth while we must think in terms of delivering, not millions, but billions of tonnes, not annually, but pretty nearly daily. 

Still, the times they are a-changin' and by now it is a matter of religious conviction that climate is a-changin' with them; and climate stable or climate unstable, human populations are growing and water resources are shrinking.

It no longer is too early to think once more of harvesting ocean water and ice. Few people realise how unstable climate really is, even without modern human culpability. Before our "industrial revolution" of the last three centuries or so, at least a dozen "civilisations", or at any rate established urban communities, were ruined or dispersed by droughts that lasted for decades or centuries.

Collapses of that type have happened on every major land mass where cities of any sort existed. The biblical seven lean years were altogether believable as a very mild instance. The very Sahara as we know it, ancient and dreadful as it seems to us, is a relatively young desert, largely having been savanna just a few thousand years ago. It was so recent a development that apparently a few immemorial Atlas cedars still survive where rare underground water sources happen to have sustained them.

Nowadays the idea of letting a large modern city die of thirst is practically inconceivable, so it is pretty certain that some drastic modern technological and infrastructural advance must be developed to supply the water they need, no matter how ridiculous such measures seemed in quite recent past.  Certainly desalination with even greater sophistication and efficiency than what we can manage at the moment will be one objective. Just a few decades ago our current desalination technology would have seemed miraculous. Improved reticulation and redistribution of fresh water already is a must. Gathering and recycling fresh water from as yet unexploited sources will be crucial. 

Various possibilities often complement each other, for instance desalination works best when the input water is only slightly impure, brackish, such as one might be able to gather from estuaries or from sea ice.  One way or another though, we need to explore and develop as many sources of water as we can, if only because different solutions will be required in different circumstances and different regions.

And we have the thirsty with us always.

Discussion of the potential technologies that I propose here were inspired by a drastic drought where I live in South Africa, though it is far too late for immediate application of this idea to that drought, and it probably is too early to take the ideas seriously at the time of writing. Anyway, we have had droughts before.

But never a drought that so threatened modern cities, and with every prospect of more and worse threats in future, anthropogenic global warming or no anthropogenic global warming.

And one must start somewhere.

How much fresh water would we need?

Think of a number…
We consume a lot of water already, domestic, industrial, and agricultural. No one knows just how much, but it definitely is beyond the untrained imagination; in fact I suspect that even the trained imagination manages only on the principle of "shut up and calculate". People in the know cannot afford to let themselves be distracted by the boggling of their minds in the face of realities. To begin now would be none too soon for rationality, though far too soon for the politicians and business powers that be.

A rough guesstimate at current global human consumption might be four teratonnes: four million million tonnes of fresh water — per year. 

That alone is nearly as much as the entire flow of the Amazon River. It amounts to a few thousand cubic kilometres, and our rate of consumption is not decreasing; in fact many millions of people, from pole to equator,  remain desperate for fresh water all their lives, and their frantic demands for entitlement grow hoarser with anguish as the ages roll, and so does their rage.

In our calculation or planning in this discussion we may ignore those desperate people; they cannot afford to do much about their situation, so a more practical beginning would be to provide a few billion extra tonnes of water per year for the typical large, affluent metropolitan region.  A billion tonnes of water occupy about one cubic kilometre, just a large drop in the global bucket. However even that drop is beyond the imagination of most people, and what is more important, the necessary scale of the engineering is far beyond the imagination of Jane or Joe Average, who seem to think that all you need to do to get all the water you want, is to install a tap.

Or, more likely, hope someone else will install it.

It would be funny if it were not so infuriatingly tragic: even more tragic than thirst.

Unless you happen to be really, urgently, thirsty.

Bulk water engineering and the design of new bulk water handling technology are not for amateurs; we already get water from many sources that Joe Average hardly dreams of. And if he did dream of it, he would be grateful to forget the dream on awakening. Most of us don't even realise that we get a lot of our water from underground, let alone from sewage when there is enough sewage. Not many people realise that many of our underground water sources are limited; using them amounts to mining of water that accumulated over thousands of years.

Such supplies eventually peter out when the water mine is exhausted, or is ruined by damage to geological formations that hold it. Or it may get polluted, in which case it may be very hard to clean it.

Many people also don't realise that much underground water is unusably salty, often saltier than seawater, and that when rainwater percolates through to salty groundwater, it becomes unusably salty in turn.  

So don't look to underground water for indefinite supplies, unless you happen to live in a blessed region where rainfall comfortably replenishes your clean water mine indefinitely and you can hope that it will continue to do so.

And dammed water, say from giant schemes like the Three Gorges dams, not only is a limited resource at any given time, but is wanted for more than relieving drought; apart from producing potable water, it has to produce power and support transport. Such applications are not fully compatible; and they compete more and more severely as the water reserves run lower.

So don't get too optimistic. We already have seen the mighty Colorado River reduced to a polluted trickle; the Nile is threatened by each of the many countries it passes through...

Watch this space; even the Amazon and Congo are not infinite


Why the poles?

We must always remember with gratitude and admiration the first sailors who steered their vessels through storms and mists, and increased our knowledge of the lands of ice in the South.
                                                          Roald Amundsen

In the sea we have more water than we can use, though not more than we can pollute; and our planet-wide problem is not a shortage of water as water, but how to separate the water from the salt. The sun provides the planet's largest still, purifiers, and condensers, but only a fraction of the usable water goes to where we want it on land, in rivers, and in lakes. Even less ends up where we can use it for domestic and industrial purposes.

To add injury to insult, the condensed water often arrives in the form of floods, always wasteful, commonly harmful, and often deadly. 

And most of what we do receive on land soon flows uselessly back into the ocean, where it once again is lost, carrying valuable soil and nutrients with it. And pollutants,

What drives that cycle is the fact that the sun heats the water, evaporating it. Sooner or later the vapour cools till it condenses or freezes.  To use the water, we must intercept it at suitable stages between salt and salt.  Some of this interception is easy, but by ignoring some of the more difficult options, we lose a great deal of water that otherwise could have been useful.

On this planet some of the largest and most dramatic regions of accumulation of fresh water are sub-polar. That is where warm air from temperate and tropical regions meets cold air, and dumps its water burden as ice in various forms.  More importantly, sub-polar regions also are where seawater freezes.

As it freezes it more or less abruptly extrudes brine from between crystals of pure ice.

These regions are remote from where most people live and work, and in those regions ice in large masses is largely in unfriendly forms. Accordingly we have paid them little attention as sources of fresh water.

But that must change.

Just as we have been grubbing for oil in ever more incredibly difficult circumstances in recent decades, so we shall need to look at sourcing water from the more challenging, but more rewarding, less ecologically harmful, sources.

Almost amusingly, we can reflect that within remote living memory, before refrigerators were standard household appliances of the affluent, the seasonal harvesting of ice was a major industry in regions such as much of North America and parts of Europe; entrepreneurs would cut blocks from frozen lakes or the like. They would warehouse those blocks, and during summer they would transport the ice to major cities such as New York. For decades in such cities the iceman was as familiar a figure as the milkman. Domestic ice boxes were designed to hold standard-sized blocks, and a suitably insulated block might keep food fresh for perhaps a week or more.

Extravagant people even made ice cream, producing the necessary sub-zero refrigeration by adding salt to crushed ice. The ice pick was such a standard household utensil that it figured in many murder mysteries. In real life even Leon Trotsky was reported murdered with one, though technically in his case it was an ice axe, and Trotsky himself never was reported to have insisted on the distinction.

Anyway, the sub-polar regions are textbook examples of where there is plenty of fresh ice at all seasons. It just happens to be regrettably inconvenient to collect and transport the permanent ice and convert it into usable form where it would be most welcome.

Oil and gold they say, are where you find them, and the places where you find ice in paying quantities, quantities large enough to slake the thirsts and cool the fevers of cities and nations, are places where you find cold. 

For example in sub-polar regions.

Nor is that all; cold is not only where you can find ice, it is where you can make ice.


So what are you waiting for? Fetch!

But the question of what to do with your ice once you have found it or made it, leaves you with whole ranges of problems. As I shall point out, the fact that there might be problems does not prove that ice is not worth finding, but it certainly means that we cannot expect half-baked ideas to solve all those problems.  We shall have to work hard to learn what to do with what we gain.

Some Practical Problems

The secret fountains to follow up, waters withdrawn to restore to the mouth,
And gather the floods as in a cup, and pour them again at a city's drouth
                             Rudyard Kipling, The Sons of Martha

Among all the practical problems we consider, we might as well start with the sheer scale of the need and the supply. Just moving the equivalent of a supertanker of fresh water is no joke. Let’s suppose it carries half a million tonnes — nothing special when one is carrying only water; convenient dimensions for a full load might be something like 420m long, 60m wide by 20m high.  Nothing special, as I said:  barely six stories high; you could hardly get four football fields on top of it and you could walk round it in less than 15 minutes.

Now, if you really think that is nothing special, try lifting or dragging a single cubic metre of ice. If you use a crane, see what it does if you drop the block or bash it accidentally. Tonne masses are big and unwieldy, but million-tonne masses of ice are unbelievably worse. Try standing by a twenty-metre ice cliff (which would be very modest; Antarctic ice shelves rise some 50m above the sea surface, and extend about 450 below). Then try to imagine how you should go about loading that into your tanker or dracone. (If you need to know about dracones,  look up "dracone barge" on Wikipedia at .)

Simple to load? Just scoop out the ice with mechanised giant ice cream scoops?

Not really so simple.  

Cold ice is quite a strong material, and the rate at which you would have to scoop it would be mind-numbing if you were to stop to think how much you would have to move to make it worth while; remember that to be worth collecting, water must be cheap and plentiful, and we need to think in terms of at least hundreds of thousands of tonnes per load, not single tonnes. And even "warm" ice — ice that is just about melting —  is a lot harder than ice cream.

And ice cliffs tens of metres high are shockingly treacherous, especially when warm. You can't just park next to them with your bulk carrier and start loading; you and your ship could be kilometres under the sea, crushed, your bones being picked over by hagfish shortly after the first unexpected calving dumps a hundred thousand tonnes of ice on you.

And if you think that towing a cargo of realistic size is a doddle once you have it loaded on a barge or in a dracone, forget it. Ocean-going tug work is some of the toughest and most hazardous on the water. It also is expensive. And slow. For towing any mass of the order of a large cargo vessel the hawsers are huge and may be kilometres long, deliberately being dragged through the water to prevent disastrous consequences if one breaks, which even giant hawsers quite easily do if there is a sudden change in tension.

Well then, instead of towing, why not load up ice into your tanker and speed directly up to the customer city?

Also not as easy as it sounds. What do you do with your ice when you arrive? Unloading will need to be fast if you don't want to go bankrupt with your ship in port, and you will need to park your payload somewhere practical as you unload it. If you want to melt it, that will take huge energy, and even if it had melted en route you would need pumping machinery of huge capacity to deliver it to your reservoirs. And reservoirs cost money too. And not just any harbour can accommodate large bulk carriers.

Might as well give up. Just sit in the corner and cry about how unfair it all is.

Actually all these problems have solutions, some more promising than others. I shall discuss some of them, but all will need proper engineering and proper economic consideration before they deliver anything.

And they won't be cheap either. We will have to learn to live with water that doesn't grow in the piles, water that costs money — more money than we have been used to paying.

Tote that Berg!

And one who licks his lips for thirst with fevered eyes shall face in fear
The palms that wave, the streams that burst, his last mirage, Caravan !
And one — the bird-voiced Singing-man — shall fall behind thee. Caravan !
And God shall meet him in the night, and he shall sing as best he can.
                             James Elroy Flecker    Song of the East Gate Warden

The traditional scheme for farming ice, was to cut slabs out of surface-frozen lakes, and some of that still gets done, but it is not an approach of much interest to our topic. It has nothing to do with transporting water to places that need it in quantities that could quench the thirst of cities and agriculture. Its very objective is not the same; those people sold ice as ice, not as water.

The needs they met were real needs, and they met them respectably, but they are not the needs that we are confronting.

We really want to deal with sources that could in principle produce billions of tonnes annually, sustainably and without serious harm to the environment; possibly even helping to conserve the environment. And we might be more interested in water than ice as such. As a matter of fact, that distinction is open to consideration, as we shall see, but we must bear it in mind.

The earliest proposals for exploiting sea ice were to tow icebergs to places like Arabia. It was the obvious option, but hopelessly unpractical. Only small icebergs are towable, and they have inconvenient shapes and their behaviour under tow is very, very bad: they topple and yaw and split and all that. Also, they cannot be towed quickly, and not only do they melt continuously en route anyway, but moving them through the water really melts them quickly. To get some idea of how quickly, treat yourself to a soda containing a few sizable ice cubes. Select a well-behaved cube, push it under the surface with a drinking straw and gently suck up the liquid so that it must pass over the ice on the way into the straw. Within just a few seconds you will erode a hollow, and in less than a minute you can melt a hollow so deep that the cube can't slip away and you can drink freely. Pretty soon you can become adept enough to drill holes through more than one cube per glass of soda.

Now imagine what liquid seawater would do to any mass of ice passing through it day after day and week after week, such as would be necessary to deliver the ice for thousands of kilometres.

This is not my personal fancy, please note; people have experimented. The idea is a non-starter.

In summary, most regions in need of water, let alone in need of ice, are hopelessly too far from any realistic route to be served by towing icebergs.

But that was the good news. Even if you could arrive off Rabat or Beirut or Kuwait with your modest little million-tonne ice cube, a hundred metres high and wide, what now? Could you pipe it ashore before it all melted? Even if you could lift it out of the water and dump it on land, how would that get it into the water supply? Such practical problems are unending. Not that they aren't soluble in principle, but in practice many of them simply are not worth solving.

Especially because, as I explained, a million tonnes of water is just a sip; you would have to keep the sips coming pretty fast if the infrastructure is at all to be worth developing.

Let's think bigger…

Ocean-going tugboats are built for two purposes: to tow huge inanimate objects 
across the ocean at a snail's pace or to slam ahead at full speed into the teeth of 
a gale to come to the assistance of a vessel in distress. Of the two, it is hard to 
say which is the most exciting. Personally, I found the long slow trips towing a 
dry-dock, a dredger or even a whole factory in the shape of a tin-dredger a more 
exacting experience than the salvage business. For, during the long trips, the 
officer of the watch develops a tendency to gaze astern instead of ahead, which 
he will find a difficult habit to lose. When, later, he is on watch on any other 
ship's bridge, pacing up and down at the comfortable walking speed that is the 
secret of relaxation, he will often experience a sinking feeling in the pit of his 
stomach on seeing the empty wake. 
Jan de Hartog   A Sailor's Life
The water from a billion-tonne iceberg would represent a significant addition to the water supply of even the largest city, but in every way would represent a challenge, both at the source and at the point of delivery...

Now, there are other approaches to towing icebergs, really large ones, in particular tabular bergs from the Antarctic, but all of them present problems of their own. The process would be difficult and so slow that precious little of the payload would get anywhere useful.  It has been suggested that by sticking to cold currents such as the Benguela, that move from sub-polar to sub-tropical seas, we could improve the parameters.


We certainly would be fools not to take advantage of such natural aids, but that is not nearly sufficient on its own. Even the coldest currents would not be cold enough to prevent ice from melting, especially when it is being towed through salt water, and as it approaches regions where the water is wanted, the air temperature would rise dramatically, causing faster melting above water level.

The natural lifespan of a large tabular berg in sub-polar water, if it has a mean diameter of some kilometres, is a few years. That is too short for towing even if towing were practical, and what is more, if we put everything we had into towing it, its lifespan generally would drop to less than a year. We would be putting all that effort into re-dissolving nearly all that lovely fresh water back into the sea instead of delivering it to a thirsty land.

Not attractive.

We could improve the balance sheet dramatically by coating the underside of the berg with sheets of plastic, using automated, remote control underwater craft, but the sheer scale of the effort would be sobering. For a comfortably sized chunk of floating shelf, say some ten kilometres across, we would need over 100 square kilometres of plastic material.
That is not in itself an unrealistic investment in material, but as an engineering feat it would be astounding. Designing the jacket to survive the trip long enough would be a serious challenge in itself; wave erosion and impact are shockingly powerful forces. Recovering the material afterwards, or ensuring that it would recycle harmlessly into the ocean in the form of innocuous fish food, would also be demanding.

Amylose film rather than non-biodegradable plastic jacketing might do the trick, but I am not sure that any realistic plastic jacketing would last well enough on the business leg of the trip. At present amylose certainly would be too costly, though one never knows...

Still, it does open tempting lines of thought. We may return...

What is so special about towing?

We need to quit arguing about whether the glass is half full
or half empty — and instead acknowledge that there's not
quite enough water to go around.
                                                                                      Kate Brown

When you come down to it, the idea of towing icebergs is naïve. Towing them certainly does save all sorts of complications and ships, with no problems other than the loss of practically all your payload and the need for special facilities at the delivery end.

With problems like that, who needs droughts and disasters?

Well then, that doesn't sound encouraging, but do we have alternatives?


Two forms of alternatives at least.

Firstly we could collect the water at the source (meaning mainly ice shelves in Antarctica, and glacier calving areas in the Arctic), and leave the floating bergs to the suckers.

Alternatively we could let a berg drift as it pleases, but begin by selecting masses suitably situated for currents and winds to deliver them efficiently; we then could proceed to parasitise them while they travel, benefiting from the distance that they drifted spontaneously. To do that we could accompany them with ships and equipment with which we could carve them up or speed up their melting.

What would that achieve?

To begin with, any payload that we could get on board a suitably designed ship or barge, no matter how slow and cheap that ship might be, we could move much faster and more efficiently than would be possible by towing the berg, and the ship could be far less dependent on wind or current. Once ice or water were loaded aboard, it would be delivered almost loss-free, without any race against melting into the sea. 

We also would need no more infrastructure at the discharge end than pumping and storage facilities. No magic iceberg-handling would be necessary. If the payload were conveyed by dracone, it wouldn't matter whether much of the ice had remained unmelted or not; the towing vessel simply could deliver the dracone as temporary storage. After delivering the dracone, the ship could prepare for the next voyage and leave with empty dracones as soon as refuelling etc were complete, possibly even before unloading the payload had begun.

In short, no towing of any iceberg would offer any attraction unless there were reason for positioning or rotating a berg. For example, a berg in a region of water too cold to encourage melting as required, might be towed, or at least nudged, towards warmer water, or if selective freezing were required, to colder.

What Sort of Vessel Should Convey the Payload?

We forget that the water cycle and the life cycle are one.
                                           Jacques Yves Cousteau

Especially in the early days of gaining experience with polar water transport, we could experiment with second-hand tankers or tugs, but as experience accumulated, we might consider designing dedicated vessels for any of at least three options, all of them on a very large scale.

Buoyancy should not be a serious problem, because fresh water floats on seawater, and so does ice. Nor does fresh water in trivial quantities such as a few trillion tonnes pose any significant pollution risk even if spilt wholesale. So, laden or not, neither sinking nor pollution should pose any special risk.

Dracones, giant sausage-like balloons containing thousands to hundreds of thousands of tonnes of fresh water or ice, have certain attractions. The filled dracones could be connected in chains many kilometres long, and towed by tugs. This is no novelty; dracones have been used in similar ways for other types of cargo for many years, though on smaller scales. They have many advantages in flexibility and low overheads. This approach could solve the storage problem at the port of delivery, and also problems of necessary delays for melting residual ice so that it could be pumped ashore after docking; once delivered and secured, a dracone could be left behind for as long as desired, while the towing vessel immediately proceeded with its next task.

All the same, towing of any gigantic load of liquid in any form probably would be slower and more costly in energy than conveying the same load in a rigid vessel. It is not clear for example, whether large fluid-carrying dracones should contain internal baffles to control resonant internal sloshing, or they should have exterior contours or appendages to improve control and attitude in the water. Possibly some sort of resonantly contracting design of concertina-like dracone would be specially efficiently towable through water, but that remains to be demonstrated, and the dynamics almost certainly would be complex. The practicalities and economics would have to be assessed in each context.

There would be a need to shuttle empty dracones, and it might not be a trivial problem to design a dracone that is manageable both when very full and nearly empty. The problem might be especially difficult if the dracone needs to be loadable either with mainly ice, or mainly water, or slurry. For example there are options for designing dracones in either concertina shapes or smooth, and with various forms of symmetry. Each design has implications for working life, scale, streamlining, tendency to capsize or twist, or whether it entails difficulties in loading, unloading, dragging line astern or dragging in bunches.

Considerations of that type need not be insuperable, but nor can the design implications be dismissed as trivial.

The design of tankers for carrying massive cargoes of fresh water and ice should be simpler than the design of drogues, but they still open several lines of approach. They could differ from any previous designs of supertankers in several ways. Unlike the largest of oil supertankers they would demand little precaution against pollution, because only the ship's fuel would be a serious hazard, not the cargo. A few million tonnes of fresh water spilt into the open sea would be a major monetary loss, but no more of an ecological disaster than a heavy rainstorm at sea. Accordingly, double-walled construction and similar precautions need not be considered unless double walls were thought worth the extra expense and weight to reduce the risk of loss of the vessel, or to reduce the rate of melting of an ice cargo.

Again, the size of the ship need not be limited by anything other than the available facilities at the designated ports of delivery and the hazards at the points of collection. In contrast to oil tankers, freshwater tankers carrying volumes exceeding a million tonnes could be routine. Any baffles, separated tanks, cargo containers, and leakage protection within the ship would be matters of detailed design, rather than basic problems.

Whether they would be considered practical at all would be open to question, especially if their cargoes were mainly solid ice. Such vessels might be very efficient in transport and collection, but they might take months to unload, so they would be major liabilities in harbour.

Accordingly a third option would be comparatively attractive: giant barges. In essence they would amount to the equivalent of the tankers, except that they would largely be unpowered except possibly for manoeuvring, pumping, and crew accommodation, if any. They variously might be manned or unmanned. Depending on their design they might or might not be connected in strings or in parallel for towing, and their design were sufficiently cheap, they might be used for ice or water storage as well as transport. If intended to store ice rather than water, they might be insulated, but independently of such considerations, they ideally should be very, very large, much like the powered tankers. Their design is open to many options, for example they might include internal baffles to reduce the possibility of rolling, and such baffles might contain cooling circuits to freeze baffles of ice. Again, they could be designed not to have any preferred way up, much like giant cylindrical barrels, so that they could roll harmlessly under all circumstances. All such decisions could be left to the engineers to deal with in the light of practical experience.

The advantages of each option would depend on the nature of the collection mechanism. For example, parking a quarter-million-tonne ship or barge anywhere near an iceberg or ice cliff, or even aggressive sea ice, might be suicidal. It might prove more practical to collect the ice or water with fleets of small foraging and loading vessels that capture the payload and process it before passing it on to the transport vessels.

Why ice?

People say that if you find water rising up to your ankle, that's the time
to do something about it, not when it's around your neck.
                                                          Chinua Achebe

Ice has all sorts of disadvantages compared to water — harder to load, less dense, further to fetch, demanding heat to make it usable, dangerous in large masses, melts inconveniently, can't be piped — the list goes on.

But some of those just can't be helped; if fresh water simply were available in any desired quantity wherever wanted we certainly would not consider prospecting for it in the form of far-off ice. As fresh water is increasingly at a premium however, or simply is unavailable in many places, we must go out of our way to get more, or we might as well stop moaning.

And from a different perspective some of the supply problems look more like opportunities.

Harder to load? Well, in some circumstances ice certainly is not easy to load; it is hard to beat efficient pumping of liquid water. All the same, as we shall discuss, suitable preparation and equipment can be developed for collecting sea ice, crushed ice, and slabs of ice. We still have a lot of infrastructure and technology to develop, but such things are necessary for exploiting any new opportunity. 

And once properly loaded, ice can't slosh about and endanger the tanker, which can be quite a problem with liquid water. Sloshing is a deadly — and costly — problem with giant ore carriers for example, in which either slurries, or even powders, slosh about and capsize the vessel. It is not exactly an everyday problem, but not rare either; world-wide, as far as I can make out, there is roughly one such event annually.

Dangerous in large masses? Too true; ice certainly is terrifyingly dangerous and in various ways too, but liquid water in large masses is no less terrifyingly dangerous — and in various ways too. Each needs its own techniques and precautions — there is no value to whingeing about it; buckle down and earn your winnings.

Less dense? Meaning that your ship can't hold so much? That also means greater buoyancy, which means that the larger storage or transport ship may cost no more to build than a ship designed to carry the same mass of water. And the stiffness of a mass of ice can be exploited to reinforce a suitably designed ship rather than decreasing its stability the way that sloshing liquid or slush would.

And the lower density means that it can burst pipes when it freezes? True, but that is more of a problem in buildings on land than ice freighters at sea. Routine problems like that are easily dealt with after the first few sinkings have taught us the first few lessons.

Further to fetch? How sad. But that only is true when nearby fresh liquid is available. Where none is available even distant ice can be worth fetching.

All these simply are realities to be approached intelligently and positively in context. That is what engineering is for.

Ice harvesting and Carbon Dioxide

      There is an old American saying 'He who lives in a glass house 
                 should not try to kill two birds with one stone.'
                             Vladimir Nabokov       Pnin

Mining or farming sub-polar ice, drift ice in particular, also offers vital advantages over exploiting seriously inadequate freshwater resources in temperate or torrid regions. The ice is plentiful and is constantly renewed whether we love it or loathe it, both in the Arctic and Antarctic, and it offers hopes of dealing with increasingly ominous threats of global warming.  

For example, removing sea ice cover increases the rate at which cold air can produce ice, and accordingly also increases the production of surface brine that contributes to the natural cycle of cold water that conveys carbon dioxide to the depths.

Such capture of carbon dioxide is regarded as very, very important, fresh water or no fresh water. Whether the effect would be significant on a global scale is another matter, but it might very well remove more carbon dioxide than the operation produces. This would in particular be true if the major vessels involved were nuclear powered or hydrogen powered.

Now, the eventual scale of the ice harvesting industry might well become one of the planet's largest. It might strip millions of square kilometres per year. As such it would be far more promising than some of the more harebrained schemes for carbon sequestration that are popularly touted.

There is a positive feedback aspect to this concept: the greater the area of sea ice that gets removed, the more water gets frozen in winter, because surface ice insulates the surface from atmospheric freezing conditions. Surface ice also prevents the solution of carbon dioxide in seawater, so, notionally, removing it could double the carbon sequestration in the harvested areas. 

Some concern has been raised about the effect of carbon dioxide in acidifying the sea water and dissolving the shells of sea life, but I am inclined to discount that, because for one thing, the effect is gradual, and there would be strong selection for animals that could manage lower pH levels. In combination with that concern, there is no shortage of dissolved calcium and magnesium in sea water, so the sequestration would depend on no more than energy-consuming proton pumps in acid-adapted organisms. 

We do a good deal of that in our own stomachs.

Ice as fuel

Some say the world will end in fire,
Some say in ice.
From what I've tasted of desire,
I hold with those who favor fire.
But if it had to perish twice
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.

Robert Frost

One major concern in all such harvesting and transport initiatives is energy. There is no room to argue against the value of ice delivered in usable form to places where it is wanted; but if we have to go thousands of kilometres to fetch it and spend months on the trips both ways, then the question of cost necessarily is very worrying.

Expensive water amounts to no water, except perhaps on a spacecraft.

And the most important cost in this connection is energy. It is not a cost we can dodge; arguably the most implacable constraints in our world are those of thermodynamics, paraphrased wryly as:

·       Do as we please to improve efficiency, we cannot do better than 100%.  
·       We cannot achieve 100% except at a temperature of absolute zero.
·       We cannot reach absolute zero.
So one thing is certain: we can't get our water free of cost.

Well, we all know there is no such thing as a free lunch.

Still, that is not the issue. The question is how far we can reduce the cost or increase the profit.

So whether the proposals in this essay stand any chance of being practical, depends on how we can cost our options profitably.

And there turns out to be more to the equation than is obvious at first sight. We need to be alert, not only for the primary objective, but for subsidiary items that can make the difference between failure and a handsome success.

I suggest, not that we can beat the laws of thermodynamics — we cannot —  but that we need to examine their fine print more carefully, looking for options that we can exploit to achieve an actual energy profit.

And part of the fine print says that what matters in exploiting energy is not how much energy we have (there is plenty of energy all about us, more than we could ever use). What matters is the exergy, which depends not on the energy in the system, so much as the difference in energy levels between one part of the system and another.

Let us call the high energy level the heat source, and the low energy level the heat sink. For example, a flame at a temperature of say 1000 degrees in a chamber at a temperature of 200 degrees notionally performs no better than a flame at 800 degrees in a chamber at zero degrees. The heat source in both cases is 800 degrees hotter than the heat sink. For more coherent detail consult the article at together with its links. This view is somewhat simplistic in practice, but has enough merit to deserve consideration.

The tempting point is that one can improve the energy efficiency of a suitably designed system just as much by reducing the temperature of the sink, or at least preventing its temperature from rising, as by increasing the temperature of the source.

Now, for most of this essay we regard the problem of importing ice as implying the need to melt it at the reception installation. And that is reasonable; there is not much we can use the water for before we melt it. And melting requires heat. And not only does it take huge amounts of fuel to drag billions of tonnes of ice through megametres of ocean, but it also takes even more energy to melt billions of tonnes of ice.

And yet, a million tonnes of ice at a few degrees below freezing point, used constructively as a heat sink, offers the equivalent of something like 334 joules per gram needed to melt it, which works out at 334 billion kilojoules, ignoring the scope for a few billion extra kilojoules to bring the melt-water to typical ambient temperatures. That is roughly the equivalent of 30000 tonnes of coal or similar fuel.

And no ash, no air pollution, no consumption of fossil fuels.

It also depends on the form in which we use that energy, but that is a question of engineering, not a matter for us to pursue here. Elsewhere in this essay I do mention the value of exposing the ice to ambient air, so as to condense water vapour, adding clean water to our yield from melting the ice. At the same time the process produces large volumes of cold, clean air, which is valuable in various industrial applications, such as air conditioning.

But those are details.

The important point is that we should be able to extract more energy from the melting of the ice, than it takes to ship ice from the points of collection to the point of consumption. One almost is tempted to argue in favour of doing it all just for the energy yield. Any water we then could extract at the point of consumption would be a mere bonus.

But one thing that matters, is the influence of such factors on the engineering strategy. One strategy is to melt the ice and ship the water, but we thereby reduce the profit in imported exergy by a factor of several hundred. We have a strong incentive to import water in the form of ice, in low-cost passive vessels such as barges or dracones that can be parked for months at the point of collection or delivery, with as little melting and as much freezing as possible until we desire to extract the water and apply the exergy to wherever it pays us best.

A temperature difference of say twenty- to thirty degrees Celsius might not seem very exciting to a power engineer, given that each degree of difference offers only about four joules per gram, but the latent heat of melting of the ice amounts to nearly eighty times as much as four joules per gram, so that shipping a million tonnes of ice to a hot climate begins to make things look a lot more attractive than shipping huge quantities of fuel pole-wards to melt the ice, even if the power engineering challenges of exploiting such a small temperature gradient seem unattractive in comparison to the many hundreds of degrees available from flame or nuclear sources.

Remember too, that the way one uses energy makes a big difference.  Energy is energy, no matter what you do to it, but when one wants to increase the efficiency of a machine by increasing the difference between the source and the sink, that can be more rewarding than using two sources of low-grade energy separately. Or one could use the cold to produce cold dry air that would take a great deal of fuel to produce by refrigeration, but would take effectively no fuel when using warm, moist air to melt the ice. Then the fuel saved could be used instead to drive the vessels and equipment in collecting ice from the sea.

Ice types and harvesting strategies

If you don’t think too good, don’t think too much.
                 Yogi Berra

Not all sub-polar ice is the same. 

In this topic let us first consider drift ice, ranging from perhaps 10 cm thick up to say three metres thick. 

More particularly, we might be interested in pack ice, that is to say drift ice that covers a good three quarters of the sea surface. Such sheets could be harvested more efficiently than chasing after individual flakes.

Secondly consider Antarctic ice shelves and glacier calvings that float out to sea after losing contact with land.

Thirdly there are the large, irregular icebergs typical of those in the Arctic; they too are from glaciers, but under circumstances different from those in the Antarctic.

Now, instead of mass ice, drift ice several years old could be precious, being easier to harvest.

Preferably we would look for sheets a metre or two thick, or fairly undistorted floes. Sheets of drift ice could in fact be so precious that prospecting for them by satellite should be rewarding. Such ice is fairly salt-free and could be collected by fleets of harvester vessels.

The design of the drift ice harvesters could be based on modifications of ice-breaker principles: unlike the traditional icebreaker, that breaks through floating ice by riding up on it till it falls through under its own weight, a harvester could invert the process by sliding beneath the crust and raising the ice in strips a few tens of metres wide and stacking them on board till the load reached capacity. It then could return the booty to the mother ship or the dispatching facility.

While the load is being processed the harvester returns to its floe nibbling.

One cannot always expect ice to break neatly, so other, cheaper utility shuttle vessels could scavenge free-floating blocks small enough to fish out of the water, a few tonnes or tens of tonnes at a time. There also is a great deal of floating trash ice that could be harvested easily, though it might be a bit on the brack side. 

Given that old ice is so much more valuable than young, because it contains less salt, it probably would be worth maintaining satellite surveillance of young ice fields until they were ripe and had thickened and shed their brine, rather than attacking them while they still are salty. 

Harvesting such well-formed sheets of ice should be relatively safe and profitable, as long as one could counter piracy. A fairly small field, say a hundred kilometres square and with a mean thickness of about 1 metre, could yield about ten billion tonnes of relatively pure ice in manageable form. Of course, that would take some thousands of vessels to collect all the harvest and deliver it to the client countries and cities. The clients in turn would need facilities to handle the imports, but those need not be any more demanding than damming and treating the water of major rivers. It also would be a good deal less costly, especially if the water were collected and delivered in the form of ice that at local temperatures could be used as a source of power or extra condensed water

Ecological objections, such as comparing notionally harmful collection of floating ice, with the undeniably disastrous ecological effects of draining rivers, would be unrealistic. The ice would get replaced faster than we could collect it, and the harvesting craft would only be worth operating where there is a lot of ice, so there would be no question of destroying any ecosystem. Harvesters would continually be leaving partly depleted fields to freeze over naturally, while being repopulated by sub-ice-pack organisms.

Young sea ice, one or two years old, generally would be less valuable than old, because it is saltier, but it still is much less salty than seawater. So where there is no convenient pure ice, it still could be worth harvesting young ice. However, older sea ice is more valuable, and easier to harvest in bulk, so giving depleted pack ice three years or so to recover from harvesting would make good economic sense without any formal legislation or control.

The big lumps

A sea setting us upon the ice has brought us close to danger.
                        Henry Hudson

Calving glaciers and irregular icebergs might well prove too dangerous to be worth harvesting, but their substance is tempting, being large masses of practically pure water. Practically all the major bergs originate on land, from snow and other precipitation, so they don't contain significant amounts of salt at any time. Even those that originate from collisions of exceptional masses of drift ice generally are old enough to have lost most of their brine.

So if we could find efficient and effective ways of cleaving them into harvestable slabs, that would be nice. I have no firm suggestions as yet, but explosives or injection of compressed gases or seawater might be used to smash bulk ice into harvestable sizes or to induce calving. ANFO probably would be the cheapest and safest explosive, but liquid oxygen mixed with fuels such as propane might have advantages of speed and cleanness.

Instead of drilling into mass ice, we might find that light artillery specially designed for shooting charges into dangerous ice masses, might work rapidly and efficiently enough to be valuable. After all, they would never need to work at ranges of more than a few hundred metres, so their construction need not meet anything like mil-spec standards. The propellant could be a gas/air system such as propane. A suitable gun based on such a principle would not need any propellant cartridge; Diesel-type compression could render ignition unnecessary. Possibly even some form of scaled-up air-gun would be practical.

Ice shelves attached to land might best be avoided for reasons of safety and possibly to avoid ecological considerations, but detached or detaching floating shelves of pure drift ice inevitably melt uselessly as they float towards the equator, so it should be harmless and sensible to intercept them in time for harvesting. A fairly realistic tabular iceberg with a harvestable thickness of 100 metres and an area of 25000000 square metres (say 5 km square) should yield about 2.5 billion tonnes of fresh water. How to harvest it is a more complicated matter, because one cannot simply skim it like cream or like sea ice.

Really large floating ice shelves, such as those of the order of 10 billion square metres would be very valuable in principle, but it would be challenging to harvest more than a fraction of such a shelf before it broke up.

Still, all in all, sea ice seems to be the most promising large scale resource; it might be possible to harvest enough shelf ice to be worth while, especially in very high latitudes, where freezing winter dark alternates with sustained summer sunlight and temperatures above freezing. As we shall see, such alternation could be exploited in various ways.

As already noted, explosive nibbling designed to detach harvestable chunks in huge quantities should be practical, and particularly valuable where the ice is weak and starting to melt faster in warmer water.

It even might be worth exploring options for tethering major ice shelves that threaten to separate and drift wastefully away. Nowadays we usually have several years of warning of the separation of huge shelves. If, by tethering them, we could slow down their separation enough to match the maximal rate of nibbling at the seaward margin and melting from above and beneath, that would pay for quite costly tethering.
But, tethered or free, where the shelf still is cold enough, thick enough, and stable enough, it actually might prove worth installing our equivalent of ice-cream scoops, though the resemblance to your familiar retail ice cream scoops would be remote. Devices like the leviathans used in open cast mining of coal could strip huge areas of ice onto transport facilities for loading onto barges or into dracones. As the upper surface was stripped from a shelf of say, 100 to 500 metres thick, the ice sheet would float progressively higher till the shelf in the mined region became too thin for stability and safety. Then the whole installation could up sticks and move on to thicker ice.

If it proved practical and worth while, the final residual layer could be broken up into suitably sized blocks for direct loading – after retrieving the valuable equipment for the next sheet of course. But it is not yet clear whether that would be worth while.

It is not clear that this strip-mining approach would compete successfully with collection of thin drift ice or nibbling at the edges of shelves with explosives, especially in the early years of the industry, but long-term exploration of the options we may leave for future generations.

The fact that ice shelves are melting from beneath and from above suggests other approaches. In the warmer sub-polar regions suitable pigments on ice shelves could collect sunlight to create ice lakes kilometres across and many metres deep, well worth pumping directly into barges and dracones. No ice breaking involved. Just spray your pigments, such as carbon or dark clay or soluble dyes, and wait till next season to start pumping.

Irregular bergs probably could not be scooped easily enough to justify the installation of equipment in the same way as big shelves, but they might well reward explosive carving or splitting into blocks for loading. Similarly, the edges of tabular bergs could be cleaved vertically or nibbled into loadable blocks. 

The fact that fresh water floats on salt has various promising implications. Barriers of biodegradable polymer foam could be extruded by robot underwater craft, forming fences beneath ice shelves in suitably chosen locations where the water is still and there is little current that could cause water exchange. The barriers' buoyancy could hold them against the underwater ice ceiling. Any molten fresh water would remain against the underside of the shelf by its buoyancy. Alternatively, the craft could carve hollows beneath the ceiling by directing seawater jets upwards. In either case, holes drilled from above down to the underwater domes could enable freshwater melt to float upwards for collection. 

Because of contact with the seawater, much of such molten ice would be brack, but as noted elsewhere in this article, even brack water is valuable. Depending on which options would be most profitable, it either could be delivered to market directly, or pumped into ponds on the shelf surface to freeze into plates of usable purified ice in winter.

Deliver ice or water?

Diarrhea, 90 percent of which is caused by food and water contaminated by excrement,
kills a child every fifteen seconds. That's more than AIDS, malaria, or measles, combined.
Human feces are an impressive weapon of mass destruction.
                                                                        Rose George

Delivery of either ice or water has its attractions and each presents its own problems. Water is easy to pump aboard in loading the harvest, and ashore in delivering the water. Water also is compact, either in itself or if we use it to fill the gaps between ice blocks in storage vessels' holds. But it also needs special precautions to handle at sea and it cannot be stacked like solid ice blocks. Also, its capacity for storing cold (or storing a deficit of heat, if you prefer to put it that way) is small, compared to that of ice. Concentrated cold can be just as valuable as heat in industry. That is why we who remain ashore spend money on freezers, heat pumps, air conditioning and the like.

Accordingly, as described, it could profitable to deliver massive ice to warm regions where suitable infrastructure is established. Ice could be used for instance in improving the efficiency of cooling towers, or in cooling and drying air, and in the process it could collect a fair amount of condensed water from warm, humid incoming air. The cold also might be used in heat pumps to freeze seawater from which pure water could be collected.

Conversely, seawater warmed by solar power or heat pumps could be used to humidify air that could melt or carve delivered masses of ice while yielding an extra profit in desalinated water.  Given sufficiently humid air, ice could condense a sizable fraction of its own mass of essentially pure water. Air that had been cooled and dried in such ways could be used for industrial air conditioning, much as one can use waste heat from power stations for combined heat-and-power schemes.

Ice delivered in such masses rather than in loadable blocks would be difficult to get off large ships or barges or dracones, and therefore would be something of a liability if it took months to unload. This would be a good reason for using low-value dracones or barges for transport. Such ice-laden vessels would serve as storage buffers while the load thawed and got pumped ashore as required.

Meanwhile the tugs that had delivered them could have returned pole-wards, taking previously emptied vessels with them. They probably could fetch a few full loads on successive journeys by the time their first load had been consumed.

Brackish ice might be expected to produce more saline water from its lower levels as it melted, the upper levels being effectively pure water, while the brack material could be desalinated and the brine dumped. Some brine would remain after desalination of brackish water until it became too concentrated to be worth further desalination. 

In contrast to the residue from desalination of seawater, the volume of brine from brackish water might be too small to be worth attention, so there would be advantages to desalinating it to no higher concentrations than the local seawater could accept without special treatment.

For one thing, that would remove the problem of disposal, because the brine then could be dumped anywhere into the sea without special precautions. The problem of disposing of brine after desalination to concentrations greater than that of local seawater has turned out to be a serious concern in practice. 

However, there is no reason to fear that suitable strategies for dispersal of brine might be difficult to develop.

The technology of managing such processes economically could become quite sophisticated. 

Why icebergs at all?

We buy a bottle of water in the city, where clean water comes out in its taps.
You know, back in 1965, if someone said to the average person, 'You know
in thirty years you are going to buy water in plastic bottles and pay more for
that water than for gasoline?' Everybody would look at you like you're
completely out of your mind.
                                                                                      Paul Watson

Icebergs, especially large tabular icebergs, are very concentrated sources of water, and in suitable circumstances are less seasonal than drift ice. They also tend to be very low in salinity. This suggests  that it should take less energy to collect them than it would take harvester craft to retrieve drift ice.

It also might be easier and cheaper to deliver potable water from icebergs than from thawed young drift ice that might be expected to be more saline. Accordingly it might be worth breaking large bergs into manageable blocks with explosives, as already suggested, after which the blocks could be loaded or broken up mechanically into loadable sizes.

Why not make the ice instead of collecting it?

 The society which scorns excellence in plumbing as a humble activity and tolerates
shoddiness in philosophy because it is an exalted activity will have neither good
plumbing nor good philosophy: neither its pipes nor its theories will hold water.
                                                                                      John W. Gardner

The primary objective is to deliver water to the thirsty clients, and for them to receive it exactly when required and pump it to where it is required is the obvious option. However, the entire operation is costly in energy, infrastructure, and human resources; the source is largely seasonal, and to consider every material saving and gain is in the enlightened interest of all parties.   

Polar ice is in many ways valuable, but it does not come presented on a tray ready for consumption, and the most convenient forms of drift ice often contain more salt than we would like, though only a fraction of the concentration in seawater. That does not mean it is valueless; we might well ship brackish water to willing clients for further processing, but at the same time, where local circumstances are suitable, we might have better uses for large quantities of brackish water than dumping it at sea.

For example, imagine a giant tabular ice sheet near Antarctica, either still landfast, or not yet about to fragment or proceed rapidly north, or tethered. Imagine that we had excavated a large, deep hollow into its upper surface. During summer we could dump our marginal harvest of brackish water into the hollow, where it would melt high quality, low salinity ice, increasing the volume of decreasingly brack water, especially in autumn. We might add a trace of dye or carbon black to promote solar-powered melting. During the sub-polar winter its surface should freeze thick, say 30 cm to 1 metre or so, and the ice in such a situation should be of high purity and undiluted by seawater: Nature's free desalination service — or nearly free anyway. Come the harvest season in spring, such effectively pure ice on a stable surface would be easy to collect from the surface and load onto transport craft.
We could assume that once the ice harvesting industry had matured, there should be a large number of dracones and barges continually available, either not yet fully loaded, or laden with brack water. They could be left with their holds for the winter. The water would freeze from the surface down, and their deeper layers would concentrate the salinity while their upper layers would improve in quality. Come springtime each vessel could be assessed for appropriate treatment, either discarding or delivering brack water or preparing it for further treatment. 

Meanwhile the harvesters could replace the discarded brine with good water pooled from other sources. 

Whether to have specialist craft for such brack water concentration and ice delivery, is an open question. We need not consider such special details seriously yet.

Why not pipe the ice instead of shipping it?

I love the sounds and the power of pounding water,
whether it is the waves or a waterfall.
                                           Mike May

This obviously sounds unattractive for clients near the equator, and there is no question of anything of the kind in the short term, but the need for water world-wide shows no prospect of decreasing. 

Meanwhile the population is increasing. 

There certainly will be an increasing need for global water reticulation. The necessary infrastructure will be far too huge to pop into existence suddenly. One of the early forms will very likely be large, long-distance ducts for shipping ice and slurry from the sub-polar regions to consumer regions.

Transoceanic ducts could be collapsible modular submarine pipelines of suitable tough plastic, each say a few kilometres long, with control and communication modules at one end or both, designed to control their buoyancy at each unit’s  appropriate depth.  They could very likely be used for communications and power transmission too, and maybe for certain types of material transport as well, very likely containerised.

The water ducts could be say a few metres in internal diameter, at least partly driven by wave power. Modules would serve simultaneously as ducts, processing units, and buffer storage. Suppose an internal cross sectional area of ten square metres; then a one-kilometre unit would have a capacity of 10000 tonnes of water. A 1000 km pipeline could act as a buffer store for holding ten million tonnes. Not huge, but enough to matter.

If a portion of the capacity were reserved for air to be fed into the warm end, it could be used partly as a source of water of condensation, and partly to melt or at least warm ice at the cold end. Where it is released at the cold end its excess pressure could be used as a source of power.  For instance it could contribute to ice breaking and loading.

Brack, schmack!

Seeing that our thirst was increasing and the water was killing us, while
the storm did not abate, we agreed to trust to God, Our Lord, and rather
risk the perils of the sea than wait there for certain death from thirst.
                                                          Alvar N. C. de Vaca

As already mentioned, one thing we cannot expect is to get pure water from sea ice. Old sea ice generally has shed most of its brine, and ice shelf and glacier ice are largely old snow deposits, so such classes of ice generally have very low salinity, but in practice we must expect pollution from contact with seawater; for example shelf ice may soak up a lot of seawater because it is porous, and some of our most easily harvested ice will be just a year or two old — it still contains too much salt anyway. To shed much of that salt would take another year or two of warming and cooling by the seasons and of massaging by storms and swells.

The old ice often is drinkable when melted, but not really up to standard for heavy irrigation and commercial potability. Really young sea ice is barely drinkable in times of desperation if at all; it might contain say 1% or so of salt. Seawater usually is somewhere between 3% and 4% salt, and realistic desalination is practicable up to roughly twice that concentration.

However, the cheapest, fastest and most sustainable desalination is the purification of large volumes of slightly brack water. It certainly is better, faster, and cheaper than trying to desalinate seawater.

Firstly, one does not simply chuck weak brack water into the machine and get out pure water plus concentrated brine. Different strengths of brine require different treatments with different membranes and pressures and energy consumption, and disposal of concentrated brines is more difficult than disposal of weak brine.

Accordingly, if one cannot provide the client with pure water, he might well be willing to pay for say 0.3% brack water, about ten times weaker than seawater, so that he only discards about 10% of the output instead of 50%. He can do so without precautions against pollution, because at that rate the discarded brine is pretty close to the concentration of seawater. For many purposes a solution about fifty to one hundred times weaker than seawater is practically usable as is, with no more discarded output than from processing most kinds of fresh water.
Mind you, do not take these figures too seriously; they are just to give some idea of the major principles. In practice desalination is not as simple as it sounds; cleaning, backwashing and so on make for some waste as well.

The upshot is that the ice harvesters need not insist on pure-water ice, but would need to assess every major item they attacked or brought on board. They would not mix relatively strong brack water with more or less potable water, and they would price the water according to its intended purpose and the amount and nature of purification or dilution it would need. No doubt such things as dates of delivery, contracts, and special circumstances would affect prices too.

Future markets in water promise to be a very interesting field of study and practice.

Ice, Infrastructure, and Commitment

If you’re achieving all your goals, you’re not setting them aggressively enough.  

Laszlo Bock

We have known for generations that the need for fresh water can only grow. Certainly in our traditional consumption of fresh water there is scope for water savings, for avoiding and ameliorating pollution and water loss, for using water more intelligently, and equally certainly we need to improve our practice accordingly, but that scope is limited. Besides, if you look into the real prospects and the requirements for those necessary measures, you find that on any major scale they are neither easier nor cheaper than anything so far discussed in this essay. Furthermore, water is needed for so many things, power, irrigation, industry, as well as domestic supply, that we cannot simply go out and collect whatever we want for any particular use; almost any water we divert to alleviate one need aggravates some other need or interferes with some other function or increases some other cost.

Our immediate problem is not to find more water; the planet has plenty for our next few centuries. What we need is to find the largest immediate uncommitted source that we can afford to exploit without harming other interests. Salt water is plentiful, but expensive to purify, even though we have made massive improvements in desalination. Anything we can do to decrease the energy cost of obtaining fresh water is worth looking into.

Now, natural processes continuously desalinate water in quantities greater than we have any need for yet, and they even store a lot of it for us in the form of ice and dispense that ice in quantities greater than we need at any particular time. Pack ice drifts till it melts, and glaciers dribble gradually into the ocean or down rivers. 

Rain and snow in temperate regions are another matter, but they already are largely claimed by various legal parties, except when they present threats of floods or mudflows. Even when we do not use them all, we cannot simply take more, or we conflict with downstream users in one way or another. For example some rivers simply get used (even re-used) completely, such as the Colorado river, or get ruined for downstream users. Damming of the Nile has practically destroyed the Mediterranean sardine fishing industry off the Nile delta, and also the annual Nile flood silting. And worse is in store; with more damming, the Nile as we know it might yet cease to exist within our children's lifetime.

Trouble is brewing around our major rivers and lakes. If you dam water you cover land. Fail to dam water, and you decrease flood control options. Use accumulated water for power and you limit its scope for irrigation, industrial, and domestic use. And whenever you empty dams you create other problems.

In short we need fresh water from elsewhere. We know where most of our surface fresh water is. We know that it is frozen, and generally the frozen water is far from where we want it. Proposals for using it have so far been pathetically naïve, for instance dragging icebergs over the ocean. Fair enough, ideas have to start from somewhere, but such non-starters have given the feasibility of exploiting sub-polar ice a bad name. 

This essay has argued that there is scope for taking the harvesting of sub-polar ice seriously as a source of water, and in fact, that such an industry is inevitable and could be developed within a matter of years.

The obstacles are:
  • It does not sound possible (much as undersea oil drilling was dismissed when the idea was proposed)
  • It will not be as easy as its proponents make it sound
  • It will take heavy investment, and in particular it will be costly to start up as an industry
  • On anything but a huge scale it never will be worth while, let alone economical
  • Harvesting and transporting the ice, whether solid or molten, will be only part of the problem; dealing with it at the point of delivery is no trivial matter either
  • Design of the harvesting, transport, delivery and application technology involves whole ranges of their own types of problems; we cannot simply think up a bright idea and expect it to work economically first time, quite apart from the problem of producing trained staff to run the industry
In short, humanity needs to generate start-up capital and infrastructure, and possibly the development of  international legal standards as well. National commitments might be necessary to encourage development. People rarely understand the scope and importance of infrastructure, so pioneers tend to come up with half-baked ideas that crash ignominiously. 

Conversely, other people stand abashed at the scale of start-up challenges, and proclaim every form of new development impossible. 

But it is worth repeating: our exploitation of natural ice as a source of water is not a matter of whether, but of when and how. It is high time to think it over at levels of authority sufficient to invest resources in the development of pioneering plans and equipment.

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