Topics: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?
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?
Ice infrastructure, and commitment
Many forms of thirst
There are many forms of thirst.
And gather the floods as in a cup, and pour them again at a city's drouth
Rudyard Kipling, The Sons of Martha
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
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.
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
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.
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...
or half empty — and instead acknowledge that there's not
quite enough water to go around.
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.
Jacques Yves Cousteau
to do something about it, not when it's around your neck.
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 DioxideThere 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 effect, 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 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.
Ice types and harvesting strategies
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.
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.
Because old ice is so much more valuable than young, 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 attack them while still salty.
The big lumps
A sea setting us upon the ice has brought us close to danger.
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.
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 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 smashing 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 other 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 relative current causing 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.
kills a child every fifteen seconds. That's more than AIDS, malaria, or measles, combined.
Human feces are an impressive weapon of mass destruction.
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.
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
Meanwhile the harvesters could fill up the spare space with good water pooled from other sources.
whether it is the waves or a waterfall.
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
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 brines 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.
Infrastructure, and Commitment
- 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