Solar and kite power also reduce costs considerably.

The container ships might be efficient but something doesn't jibe with what you're saying about how high oil would have to go to make a difference.

Here's how I derived my estimate:

Bigger is more efficient and high oil price will drive ships as big as can be accomodated. I base my estimate on the numbers from Emma Maersk(and by extension its sister ships; over 10 of which are either completed or in construction).

It can carry 11 000 20-foot containers, 14 MT each. An empty 20-foot container weighs 2.2 MT. 11 000*(14 - 2.2) tonnes = 130 000 MT of goods.

It has an 80 MW wärtsilä engine as main propulsion with an efficiency of 52% and 5x6 MW caterpillar 8M32 engines(couldn't find the efficiency numbers so I used 38% fuel efficiency, which I estimated from a smaller 5 MW marine propulsion engine on caterpillars website). Maximum fuel consumption is 80 MW/0.52 + 30 MW/0.38 = 233 MW.

It has a top speed of 29.3 mph and a cruising speed of 21 mph. To sustain the top speed it will presumably use all engine cranked up to maximum, consuming the full 233 MW.

29.3 mph is 13.1 m/s. Fuel intensity per km is 233 GW/(13.1*10^-3 km/s) = 17.8 GJ/km.

Dividing through by mass we get fuel intensity per weight: (17.8 GJ/km)/(130 000*10^3 kg) = 135 J/(km*kg). To get a feel for how efficient that is; moving a 1 litre carton of juice 1 km costs as much energy as your body consumes in ~1.5 seconds while you asleep.

Right, but you're not going to ship things at maximum speed because drag goes as the cube of speed and as a result mileage will be proportional to the square of speed(ignoring slight variation in energy efficiency for the time being.). At 21 mph, which is the cruising speed of Emma Maersk, fuel intensity will instead be ~135 J/(km*kg)*(21/29.3)^2 = 69 J/(kg*km). Average engine efficiency including the caterpillars is 48%, with caterpillar auxilliaries turned off it is 52%; adjusting for this we get: ~69 J/(km*kg)*0.48/0.52 = 64 J/(km*kg).

As you mention below, slowing down is a common way to mitigate fuel costs. Slowing down a little bit to ~18-19 mph would bump that number down to 50 J/(km*kg).

The top of that fuel intensity range will be avoided when oil is expensive, so I took 50-100 J(km*kg) as a reasonable estime of fuel intensity for current technology.

A t-shirt weighs about 200 grams and half the earth's circumference is 20 000 km. Using the above fuel intensity that comes out to 0.2-0.4 MJ thermal energy, which is 6-11 ml of oil, which comes to 1-2 tea spoons.

Low-value, bulky goods are the first to feel the strain, as you would expect.

Nobody will grow bananas in Vermont and Brazilian iron mines won't move to a Pittsburgh suburb. Some business models can be unglobalized and others can't.

It doesn't matter. Reducing oil dependencies doesn't need to be an all or nothing affair. What is needed is to reduce usage enough to meet the constraints of supply. A long continuing trend of unglobalizing what makes sense will help for a long while.

For agriculture an hybrid model may prove workable. There are markets around where I live selling local products. It doesn't mean industrial agriculture has stopped. Both models coexist. But increased reliance on local products still saves some oil.

Because as oil and NG costs go up, along with everything dependent on them, industrial and globalized agriculture will collapse, and we will be left in a far more precarious state than had we not begun localizing earlier.

I don't think maintaining centralized farming indefinetely is going to turn out to be that difficult if(and only if) we can fix the food distribution system; that's the major source of oil consumption in food production and I've seen nothing that will allow long distance trucking to continue. There are wild-cards like EESTOR; I'd love to believe it's true but that just seems like a bunch of hot air too me.

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Farm machinery is a relatively small consumer of oil. Things have probably improved since 1996, but here's a corn ethanol energy balance study with good data on the energy inputs to farming corn: http://www.usda.gov/oce/reports/energy/aer-814.pdf

Here's the relevant 9-state averages:
Diesel Gallons/acre 8.6
Gasoline Gallons/acre 3.09
LPG Gallons/acre 6.36
Electricity kWh/acre 77.13
Natural gas Cubic ft/acre 200

If you're wondering why there's such a diverse distribution of energy sources when diesel is used for most farm equipment, it's because much of this energy went into drying and processing the corn(some states even used diesel fuel for drying corn; I suspect this practice has ended). At some point, waste heat from a power plant, solar concentrators or natural gas from anaerobic digestion of corn cobs or some other source will make more sense than continuing to use the above. The most difficult part is replacing the diesel for the vehicles, which cannot be tied directly to the grid; pessimistically that's about 10 gallons of diesel per acre, probably much less with no-till and the most efficient farming machinery available today.

10 gallons of diesel allows you to plant and harvest ~140 bushels of corn; that's 3.5 metric tonnes.

Fertilizer is a far bigger energy input and the greatest of these is nitrogen. All you're doing with the natural gas is to steam reform it and use the water gas shift reaction to get more hydrogen gas: total reaction is CH4 + 2*H2O = 4*H2 + C02.

The low-hanging fruit is to substitute methane with coal and do the same trick; you'll get 2*H2 per carbon atom(and a little bit extra since coal isn't pure carbon). It's not as cheap as stranded natural gas, emits more CO2 and heavy metal pollution, but it puts a reasonable cap on the price of fertilizer. This is off the shelf tech and is in use for hydrogen gas production right now.

There are potentially more interesting methods of producing hydrogen. You can produce methane from left over biomass in an anaerobic digester. Not all materials are suitable, but according to http://www.chpcentermw.org/pdfs/061211JasperIN/Sievertsen.pdf if corn stover is digested toghether with manure you can recover as much as 50-75% of the heating value of corn stover as methane. The co-products are nutrient rich liquid that is usable on-farm and nutrient rich compost-like solids useful as fertilizer.

Pyrolysis of biomass is another way to produce some hydrogen gas. Economics will depend on how valuable the coproducts are and how much of the mineral fertilizer can be recaptured in the char fraction. Different kinds of char are being investigated for improving soil fertility(seems to have been born out of the realization that the amazonians used low temperature wood char to make dark, fertilze soils called "terra preta"), as a bonus char is a way to sequester carbon for a long period of time in a stable form. You also get something called pyrolysis oil, which is quite corrosive and not a good substitute for petrolueum in vehicles, but contains interesting and potentially valuable chemicals that could be isolated and is just fine as heating oil(could be used for drying corn).

A pebble-bed reactor or molten-salt reactor capable of operating at 850 degrees celcius can use the thermochemical sulfur-iodine cycle to convert as much as 50% of it's thermal output into hydrogen gas from water. The waste heat is still hot enough to produce a little bit of electricity and could be used for district heating.

Instead of trying to build HVDC lines all across the continent to try and smooth out wind variations you could dump excess wind power into big electrolysers such that you manage to maintain some low level of power output from the wind turbines most of the time and you clip off the peaks with electrolysis. Very clean hydrogen that can be easily used for haber-bosch. Oxygen gas co-product that can be pressurized and sold(hospitals, welders?). Could use stranded wind-resource that nobody wants to develop(the cost of power-lines is a very big part of the economics of wind turbines).

And last but not least, if the economics work out you could produce ammonia directly from electric power, nitrogen gas and water without electrolysis and haber-bosch; this would be more efficient and could be used in the same way as electrolysis. See http://www.energy.iastate.edu/Renewable/ammonia/ammonia/2007/SSAS_Oct200... for more information.

In addition we are getting better at supplying fertilizer to plants when and where they need it; this is being driven by a desire to reduce fertilizer run-off and high fertilizer costs. We're getting better at no-till agriculture which leds to less water loss, soil and nutrient erossion.

None of these ideas may be practical for a full-scale "hydrogen economy", but ammonia production is a much smaller problem than all transportation.

As for the mineral fertilizers they are mined. The uranium available in the phosphate ore is more than enough to power the machinery required to mine the mineral fertilizers and ship them by rail to their destination(50-200 g of natural uranium per tonne of phosphate rock; if you only extract half of that it is 5 to 20 barrels of oil worth of heat with current reactors(lots of room for improved burn-up even without breeders; all reactors get some of their energy from plutonium but don't necessarily produce as much Pu-239 as they consume fissile U-235 and Pu-239), and it's fairly easy to get at with leaching(the industry shut down when uranium got too cheap but it may be revived when there's no more highly enriched uranium from russian thermonuclear "sparkplugs"). Much of the mining machinery is stationary or near stationary(drag lines, pumps, crushers, slurry pipelines, conveyors...); it either is electrified already or can easily be grid connected and powered by electricity.

Processing of the food into something you'd actually want to eat is non-trivial. The usual method in the western world has been to feed it to animals; chicken being reasonably efficient and beef being terribly inefficient; but if worst comes to worst, even polenta(corn gruel essentially) or corn bread is better than being hungry. But if you're not going to feed it to cattle you might as well grow a more efficient and appetizing food like potatos(10-20 tonnes per acre is possible in a good location!) or a more nutritious food like amaranth.

(disclaimer: I'm rather tired right now, so if something in the above seems terribly wrong, it probably is.)