The climate problem is caused by too much carbon dioxide in the atmosphere. How much do we need to remove?

Here are some estimates from the New Scientist magazine.

The "gigatonne gap" looms large as UN climate talks in Cancún, Mexico, enter their final days without new commitments from big polluters to cut their carbon dioxide emissions. A five to nine-gigatonne gap, to be precise. That is the gap between what has been pledged and what is needed to avoid dangerous global warming.

To keep the world on track to cap global warming at under 2 °C by mid-century, rising CO2 emissions should be kept below 44 gigatonnes a year in 2020, more than a third higher than today. But the UN Environment Programme warned here today that current national pledges would leave 2020 emissions anywhere between 5 and 9 gigatonnes too high.

Fred Pearce on gigatonnes of carbon

This indicates the range of extraction we need.

 The purpose of this project is to collect energy from a solar-derived source, to absorb carbon dioxide from the atmosphere and to produce a solid store of carbon to prevent it getting back into the atmosphere. The project should be self-sustaining by the sale of energy and products. At present (2009) politicians hope that injecting carbon dioxide into depleted oil wells will be sufficient. In reality there is no reason to believe this process will be either effective or affordable. It won't be effective because it doesn't put enough carbon out of use by several orders of magnitude; it won't be affordable because it has no saleable product. Sequestration needs another technique that will remove much larger quantities of carbon, and will make a profit.

Is it possible that the world's natural systems will remove the carbon that has been added to the atmosphere? That is, can the oceans (the main sponge of carbon) be relied on to remove the carbon by photosynthesising it in a reasonable time? To rely on this process to bring the atmosphere back to the pre-industrial state would seem to be rather too hopeful. If there is evidence that the sea can do it, let us see it.

How should the Human Community react to the Climate Change now underway?

• 1. By recognising the cause of the change: 200 years of burning the carbon stores in the earth: coal, oil and methane gas.
• 2. By investing on a large scale in a new energy system derived mostly from solar input, with some from geothermal and tidal.
• 3. By putting the carbon back into a safe form, taking it out of the atmosphere and oceans (where the increased acidity is causing many problems.

The last item points to the need for industries capable of reversing the 200 years worth of carbon emissions in something like the same time scale.

 1. OTEC plants at the coasts of Arid areas.

These will produce:

• a) Energy in the form of electricity, some of which may be converted into hydrogen for export.
• b) Fresh water from distillation as a by-product.
• c) Nutrient rich water from the cold sea bottom to encourage growth of sea plants for fish farms.
• d) Cold water for cooling purposes on land.

2. Spirulina Hydroponics

Using the fresh water from the OTEC plants and solar radiation Spirulina will be produced. These will absorb carbon dioxide from the atmosphere. (This has nothing to do with the various quack "remedies" associated with this organism.)

3. Plastics manufacturing from the Spirulina. From the point of view of geotherapy the need is to convert the carbon into a solid long lasting form that will not return to the atmosphere until long in the future (hundreds of years). It has taken about 200 years to raise the carbon dioxide level and so may well take a similar time to get the level down again.

Has any work been done on a plasticising process? I would like to hear from anyone who is working in this field.

Geography
As always, detailed research is needed. For example, the Atlantic coast of the Sahara is dry partly because the sea temperature is lowered by a deep upwelling of cold water, which means that the surface temperature is not in the usual range for OTEC (see this site). However, the coasts of Mauretania, Western Sahara and Morocco should be considered because there is an acute need for fresh water but also space available for Spirulina production. The surface water can be warmed by exposure to sunlight in shallow lagoons. This does increase the capital cost of the OTEC plant, but probably not the operating cost.

Experimental and Pilot plants
Other useful sites are: Somalia and Australia. Western Australia, as a developed tropical country - the equivalent climate area to the Sahara - would be the best place to run an experimental model. A piece of the Western Australia coast should be used to set up:

• OTEC plants
• hydroponic Spirulina plants
• plastics producers to polymerise and make permanent the Spirulina products
• building materials factories

The further away from the Poles the stronger is solar radiation. The aridity of the land means that few people live there and the vast acreage of hydroponics can be placed there without displacing the local population.

Economics
The aim is to create an ecological industry that pays its way and fits into the world economy as it adapts to the necessity of climate control. We can assume that what is at the present considered "conventional" energy - oil, coal and natural gas - will be scarcer than it is now and under pressure from increasing demand after the point of peak oil. That is, its cost relative to labour and other resources will be rising on a foreseeable upward graph. Thus even if there is not a regime of carbon levies there will be a demand for substitutes. It is probable that the most tradable of these will be hydrogen derived from non-depletable sources. Therefore the hydrogen from the OTEC and solar plants will be the main source of income for the project.

It is likely that by the time Climate Change has been recognised as a serious present danger, a Carbon credit system will be in place. Possibly the radical marketisers - followers of Milton Friedman - will have lost influence so that a straight carbon tax will be implemented simply to discourage carbon emissions, if the moral sense of the emitters isn't sufficient. By the time this project gets started there should be megawatt sized OTEC plants, capable of producing large amounts of energy and desalinated water. Moreover there will be a sense of urgency, at present lacking from climate discussions, and a need to absorb the carbon already loose in the atmosphere will be considered acutely necessary.

• 1. Sale of energy
  OTEC plants will produce a base load of electricity, as they can run night and day. This energy will supply the industrial area which will be created by the whole project. Solar electricity will also be available and may be sold as hydrogen, derived from splitting the fresh water produced by the OTEC plants.
• 2. Carbon credits for energy. These will be derived from the sale of permits to emit carbon dioxide. By the time projects like this one are operating the consumption of oil and coal should be declining, and the world's energy increasingly supplied from hydrogen and its derivatives. Probably the need for carbon credits will gradually diminish as alternatives to carbon emitting fuels become closer in price to the remaining fossil fuels.
• 3. Building products from the polymerised products of Spirulina. The second object of the Sahara Project is to take the carbon dioxide out of the atmosphere. To do this needs the conversion of the hydroponics products into salable materials for building, furniture, and other purposes to be devised. This industry too should attract carbon credits because these products will be replacing cement, a material that emits huge amounts of carbon dioxide in its manufacture and is bound to be charged for its emissions.
• 4. Other sources of income
  Unlike OTEC plants in the Caribbean and other seas that generate cyclone storms, the west Saharan ocean (and the Indian ocean off the Australian and Somali coasts) does not need to be cooled and there is not likely to be any effect on hurricanes. However the deep water is known to be rich in nutrients so that the local fishery is likely to be improved and there may well be scope for large fish farms to grow fish that thrive in both warm and cool waters.

Megawatt sized OTEC plants will have large quantities of cool water which can be used instead of electric air conditioning in local buildings, and possibly for some industrial processes.

In general the whole project area will become an important new industrial area stretching along much of the northwest African coast, and probably for some distance inland (how far is it economic to pump the desalinated water?). This has implications for politics, and there may well be new cities in the area. At present the area supports nomadic animal herders whose livelihood is very difficult because of arid conditions in the Sahara itself and the neighbouring Sahel region. A Somali project would be useful in providing an income for people who at present resort to piracy because there is no economic activity. A taxable income would support a proper government.

Another area where carbon fixing could be encouraged is north Western Australia. Here too is an area of arid desert near an Ocean with potential for solar input. Because it is a developed country Australia would be a good area for an initial research project but in the long run would also be a useful site for seriously large installations (a useful economic replacement for the agriculture of southern Australia, as that area becomes arid, and also for the coal exports which have to be phased out).

Australia is the developed country most likely to be seriously damaged by climate change as almost all of its current economy will be made impossible. The southern agricultural area will wither as the rain belts retreat into the Southern Ocean. The coal exports must cease after coal is banned as a source of energy.

Research and Pilot projects
Practical work should begin as soon as possible.

• to discover what inputs would be needed (other than desalinated water and sunlight)
• what output can be expected (weight of carbon fixed material)
• in general the best techniques and the best use of capital

Observer article on solar power in Sahara