Before we consider the element carbon, let us first consider that magnificent wonder of Classical Greece, the Parthenon, which was built partly out of it. That is, out of calcium carbonate in the form commonly known as white marble:
[The] Temple of Athena Parthenos (‘the Virgin’) on the Acropolis at Athens; built 447–438 BC by Callicrates and Ictinus under the supervision of the sculptor Phidias, and the most perfect example of Doric architecture. In turn a Christian church and a Turkish mosque, it was then used as a gunpowder store, and reduced to ruins when the Venetians bombarded the Acropolis in 1687. [0.5]
The Parthenon was intact from 438 BC until only 321 years ago. The decision by the Turks then in occupation of Greece to use it as they did is deplored everywhere today, and I dare say even in modern Istanbul. Admittedly though, the Turks did need a store for their gunpowder.
An earlier example of short term thinking and callous disregard for posterity resulted in the deliberate destruction of the great library of Alexandria, probably in AD 272. Much of classical literature was lost forever as a result. [0.55]
However, even these travesties were capped by a decision made one night in 1930 by Wilf Batty, a Tasmanian farmer. Hearing a commotion in his fowl house, Batty reached for his rifle and a short time later shot dead the world’s last known wild thylacine, the marsupial carnivore they called the ‘Tasmanian Tiger’. [0.555]
Today all sorts of suggestions are made as to how thylacines might be reconstituted (at huge expense) from the DNA of pickled museum specimens. But it could be said in Batty’s defence that he was operating according to the conventional rural wisdom abroad in Tasmania at the time. Moreover, he probably believed that both chicken and egg came first.
My following argument is that humanity today is poised on the brink of making a short term political decision so potentially catastrophic in its implications as to dwarf the sum total of all preceding historic blunders. I refer to carbon capture and storage (CCS), at least as presently envisaged.
The best general critique of CCS is that of Greenpeace, entitled ‘False Hope’. [0.5555] The argument set out in that document is that CCS:
- cannot deliver in time to avoid dangerous climate change;
- wastes energy.
- is risky.
- is expensive, and
- carries significant liability risks.
While generally endorsing the Greenpeace series of arguments, I add two more: (6) that carbon dioxide (CO2) although a greenhouse gas (GHG) and today rightly seen as an atmospheric problem, is none the less a resource that humans in the short term of future historic time will likely see as important for controlling the world’s climate; and (7) that as CO2 is a fundamental nutrient of plants and therefore of the whole biosphere, it is a resource that we cannot afford to waste, particularly as the world population expands and demand for plant and carbon-based products increases, while simultaneously the supply of fossil carbon and its compounds and products decreases.
In the general public and private discussion of the issues relating to climate change, Global Warming and the Garnaut Draft Report , reference is commonly made to the ameliorating effect possible through the geosequestration of CO2. This gas is added to the atmosphere by the combustion of carbon-based fuels, and at a greater present rate than can be coped with by the natural systems that remove it from the air. This is arguably leading to dangerous levels in the atmosphere, which the scientific consensus agrees will in turn result, if unchecked, in catastrophic climate change and global warming.
As the reader is probably aware, the CO2 in the Earth’s atmosphere acts in a way that can be likened to that of the glass of a greenhouse, with a net effect of allowing in (higher frequency) incipient solar heat radiation, but allowing less of the (lower frequency) returning radiation to escape. The actual Greenhouse Effect is a bit more complicated, but this net effect remains the same. [1.1]
Most countries of the world have some fossil fuel resources, most commonly coal. But few are exporters. Australia is one of the world’s top six exporters, along with the United States, South Africa, Canada, Indonesia and Colombia. Between them, those countries account for about 80% of internationally traded coal.  As coal is now Australia’s biggest single export earner, the Federal Government is eager for a way to be found around the greenhouse problem its end use as fuel creates. Geosequestration of the carbon dioxide, whereby the gas is trapped at the site of production, liquefied under pressure, and removed for burial deep in the Earth at other suitable sites, is seen by the coal industry as the best answer to the problem.
Before we examine that, I would ask the reader to consider the role carbon plays in the makeup of the planet and its biosphere. The masses involved are so huge that the most practical unit to use in discussion is the gigatonne (Gt). (1 Gt = 1,000,000,000 tonnes, or in scientific notation, 1 x 10^9 tonnes, which in longhand is 1 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 x 10 tonnes. A tonne, in turn, is 1,000 kilograms.) A block of bituminous coal 800 metres high and of length and breadth both one kilometre, would have a mass of one gigatonne.
All the world’s land plants together contain about 610 Gt of carbon, chiefly bound up chemically with hydrogen and oxygen in the form of lignocellulose, the major component of their woody and reinforcing tissue. The atmosphere actually contains more carbon (as CO2) than there is in all the land plants put together: 750 Gt are in the air. (The total mass of the atmosphere is about 6,700 times larger than that, at 5.1 × 10^6 Gt. Carbon dioxide is in turn only about 0.04% of the air mass, by what chemists call molar content.  It would be exactly the same percentage by weight, and much the same by volume.)
Soils contain a greater mass of carbon still, at 1,580 Gt, which is a bit over twice that found in the air and 2.6 times the total mass in the land plants growing in them. However, this is minor beside the carbon mass in the oceans, which has been assessed at 39,000 Gt (that is, 25 times the mass in the soils). It is made up of living organisms, their shells, skeletons and the limy remains of these lying on the beds of the oceans and seas.
The earliest known fossils of living organisms date from around 3.5 billion years ago.  These are stromatolites, or colonies of cyanobacteria (formerly called ‘blue-green algae’). The very earliest living organisms would almost certainly have been something similar to modern ‘chemical-feeding’ chemosynthetic bacteria, rather than to modern photosynthetic cyanobacteria, because chemosynthesis (deriving energy from chemical sources, such as submarine volcanic vents or ‘black smokers’) would have been possible long before photosynthesis was.
Consider now the last in our list of carbon deposits: the rocks. Here carbon is mainly found as carbonate combined with calcium; sometimes also with magnesium, and less often, with such metals as iron, nickel and copper. Because calcium carbonate is so commonly found in association with fossilized life forms, it is reasonable to assume that life has generally been involved in its formation, and from earliest times.
Here also, we come to the major repository of carbon on earth: the rock layer, or lithosphere. Specifically, the carbon is mainly in the sedimentary rocks, which are the most common rocks covering the Earth’s land masses, but only make up about 5% of the Earth’s overall crust. There are 65,000,000 Gt (or 6.5 x 10^7 Gt) of carbon in the rocks. It is found most spectacularly in the vast beds of calcium carbonate (as limestone) which underlie such places as the Nullarbor Plain, but it also occurs as small carbonate cementing particles in many rocks such as shales and sandstones. Put some vinegar on a piece of Sydney or Hobart sandstone and it will fizz, as the calcium carbonate cementing the stone together reacts and releases CO2.
The world really has only one ocean. The total mass of the hydrosphere (ocean, lakes, rivers etc) is about 1.4 x 10^9 Gt  and over 98% of it is oceanic salt water. That is, the total mass of carbon in the world’s carbonate rocks and minerals is a relatively huge 4.6% (nearly one part in 20 by mass) of the water in the ocean. If all that carbon was once in the early Earth’s atmosphere as carbon dioxide and methane, and much of the oceanic water was in the air as well as water vapour, that air would have been impenetrable to light. Life would have had to start through chemosynthesis, unless it began at the top of the cloud layer.
To get from the air to the lithosphere, our rock carbon probably spent some time as a component of the primordial ocean. To model that situation, one can take a level teaspoon of Vegemite and fully dissolve it in 19 teaspoons of warm water. The resulting dark liquid is a sample of ersatz primordial ocean. The first chemical feeding bacteria would possibly have converted that rich soup of organic compounds into a swarming population of their descendants. If the chemical feeders did not do it, then the later-evolved photosynthetic cyanobacteria certainly would have. The water of the ocean before life began would have been as if straight out of a pot of minestrone; shortly after life began, as if out of the most slime-infested stagnant pool one can find today. But over the course of evolutionary time, most of its carbon made its way into the bodies of multicellular organisms, then into the carbonate rocks, the oil and natural gas deposits, the land plants and the coal seams of the world. In one of those rare and rapidly transforming events in the history of the Earth, exponential growth of the first populations of photosynthetic organisms would have cleared the ocean water.
It is important to remember, however, that for a while there in the Precambrian (say for at least 1,000 million years after life began) pretty well all of the world’s carbon was probably cycling through the biosphere, with enough locked up in it at any one time to hold the atmospheric CO2 concentration sufficiently low as to prevent the planet from overheating, but at the same time with enough being respired back into the air to prevent the planet from freeze locking. Carbon moved out of circulation and into sedimentary rock would have been replaced, at least in part, by that issuing forth from volcanoes. (Though there seems to have been the odd interlude in geological time when this mechanism gave trouble. [5.25])
The early biosphere, though consisting then of much less complex life forms than we see today, must none the less have been huge by today’s biomass standards. That is something I see as being of crucial significance in dealing appropriately with the present carbon and petroleum resource crises, of which more below.
After the formation of life, photosynthetic cyanobacteria would have steadily removed CO2 from the air and ocean and deposited it as calcium carbonate stromatolites, such as those still found today at Shark Bay in Western Australia and fossilised in the Gunflint Chert of Western Ontario, which was laid down between 2.3 and 1.9 billion years ago. [5.5] Such natural geosequestration has continued to this day.
After the main rock and iron mass of the planet (literally) fell together, the Earth’s primordial atmosphere was likely formed by outgassing of volcanoes. Volcanic gases today consist of around 1.4% CO2 . The atmosphere of Venus is 96.5% CO2 and 3.5% nitrogen , and that of Mars is 95.32% CO2, 2.7% nitrogen and 1.6% argon.  Titan, which is the largest moon of Saturn, has an atmosphere 98.4% nitrogen, with the remaining 1.6% being methane (CH4) and traces of other gases such as hydrocarbons.  It is likely therefore that the Earth originally had just such a ‘reducing atmosphere’, with a larger component of CO2 and significantly greater mass and pressure than the oxidising atmosphere it has now. Its oxygen came only after the first photosynthetic bacteria appeared.
However it must be pointed out that not everyone agrees with this. 
The carbon in the carbonate rocks is mainly in the form of carbonate ions, which can be thought of as electrically charged CO2 molecules, each with an extra oxygen atom bonded on. These form when carbon dioxide reacts with water to yield carbonic acid (soda water). Being already in a fully oxidised state, they are not capable of serving as fuel. However, they are used for making cement, and in that process they are strongly heated with powdered shale in kilns, which drives the carbon dioxide out, leaving highly alkaline cement. Once mixed with water and allowed to set, this substance slowly reacts with the CO2 of the air to form calcium carbonate again, over tens or hundreds of years. So all the concrete in the world is a slow CO2 sink.
The carbon we use as fuel was sequestered after the rise of the land plants, the first fossils of which appear in sedimentary rocks of Silurian age (laid down between 443 and 417 million years ago.)  But the period of geological time that stands out for coal formation is the Carboniferous (354 to 290 million years ago), there followed, as the race callers say, by the Permian (290 to 248 million years ago). The formation of coal, oil, natural gas and limestone are processes which have never ceased, and can be seen still going on today. Nothing on the face of the Earth or under it is static; everything material is part of some cycle or other. We reading members of the human species are not just passive spectators in the drama of birth, death and decay; we actively intervene in all known processes, and sometimes not even consciously.
How much carbon is in the coal, as distinct from the rocks generally? 909 Gt, of which 479 Gt are high grade (bituminous coal and anthracite) and 430 Gt are sub-bituminous and lignite (ie brown coal). The world’s remaining oil deposits contain another 130 Gt, and natural gas another 110 Gt. As the mass ratio of the carbon in CO2 to that of the whole molecule is 12:44, considerably more CO2 by mass will be produced as compared with the mass of fossil fuel burnt; particularly coal, which is 50-80% carbon. Note also that the 1,150 Gt of total fossil fuel carbon is only one 57 thousandth part of the total carbon in the rocks, which as we have seen, is 65,000,000 Gt. (The carbon statistics above are from a Columbia University source. [11.5])
So the remaining coal reserves contain 79% of the fossil fuel carbon, the oil reserves 11%, and the natural gas reserves 10%.
Had we humans not appeared on the Earth, the great coal seams would have slumbered on deep under its surface, until a time millions of years hence when they were dragged down below the continents in the subduction zones: those fault lines where one crustal plate makes its uncomfortable way beneath another. Their carbon in due course would have transformed into volcanic gas, oil, soot, or diamonds as big as the Ritz; who knows? There has not been enough time passed yet for anyone to find out. Eventually it would all have returned to the air some way or another, to begin its cycle anew. Homo sapiens has just hurried it along a bit, that is all.
What then, should be the future for all that carbon, and right at this instant of geological time, for the carbon dioxide produced everywhere by combustion of fossil fuels?
A few months ago an article in The Australian by Dr Nikki Williams, CEO of the NSW Minerals Council, caught my eye. It was the title more than anything: ‘We can bury carbon dioxide forever’.  Her major claim I found most intriguing:
Since 1996 at Sleipner in Norway a million tonnes of CO2 a year has been captured and stored 1000m beneath the seabed in the Utsira aquifer. This formation is large enough to store all of Europe’s 600 billion tonnes of CO2 emissions for the next 600 years. Since 2000, when monitoring started, there has been zero leakage. The Norwegians are confident that it will remain in situ indefinitely, just as natural gases and oils have remained safely underground for millions of years.
I take her word that Europe will produce 600 Gt of CO2, containing 12/44ths of that mass (164 Gt) of carbon some time in the next 600 years. On the face of it, she is probably right. I also take her word about the confidence of the Norwegians, but that is all I take on that front.
Steve Furnival, a reservoir engineer at Senergy Ltd, in Aberdeen, UK, has written a detailed article  on CCS and Sleipner. His aim is to explain how “capturing and burying the carbon dioxide produced could help avert disastrous global warming”, so he does not approach the issue from the Greenpeace end of the arena. He says:
Carbon storage is not just wishful thinking: there is already a successful CCS scheme operating in Norway. The Sleipner gas field was discovered in 1974 and is one of the largest gas producers in the Norwegian sector of the North Sea. However, the gas in the field contains 4–10% carbon dioxide, while typically less than 2.5% is required to ensure the gas will burn properly. In almost any other country, the oil company would have removed the excess carbon dioxide from the gas and vented it into the atmosphere. But under Norway’s environmental laws, Statoil – the state oil company – would have faced an annual carbon-tax bill of about $50m for this option. Instead, Statoil researchers investigated storing the carbon dioxide in a nearby geological formation: the saline aquifer called Utsira that lies above the Sleipner field. Utsira is a massive formation: at some 500 km long, 50 km wide and 200 m thick, it has the capacity to store 100 times the annual volume of carbon dioxide emitted from all Europe’s power stations. 
Now this is a bit tricky, because CO2 comes out of power stations as a hot, low density gas. One assumes that this refers to final liquid volumes of CO2. From the above figures, if it were all hollow space, and the shape of a rectangular prism, the Utsira aquifer would have a volume of 5 x 10^12 cubic metres, or 5,000 cubic kilometres. Hollowed out, it would have space enough for the world’s reserves of coal and oil six times over.
The reader may have noticed that Furnival’s “100 times the annual volume of carbon dioxide emitted from all Europe’s power stations” is a bit at variance with Williams’ “all of Europe’s 600 billion tonnes of CO2 emissions for the next 600 years.” But we will let that pass.
Furnival goes on to say:
After several years of experimental study, a commercial plant was installed on the Sleipner platform in time for the start of production in 1996. Two MEA [monoethylamine] absorber columns were installed that reduce the CO2 content of the gas to 2.25%. Four compressors – standard items of equipment on most oil and gas platforms – are then used to pressurize the nearly pure excess carbon dioxide to 80 × 10^5 Pa, before it is injected into the base of the Utsira aquifer 1 km below. The high pressure is significant because carbon dioxide has a “critical point” at a temperature of 31 °C and a pressure of 74 × 10^5 Pa, beyond which it exists in a “supercritical fluid” state with a density of about 700 kg m^–3 [ie 700 kg/cubic metre]. Since injecting CO2 will raise the pressure in the aquifer, the CO2 remains in this fluid state.
Although much denser than a gas, the supercritical CO2 is less dense than water so it will start to migrate upwards. Understanding where and how this fluid moves is the main issue for ensuring long-term capture, and one that is being addressed by teams of geologists, geophysicists and reservoir engineers employed by oil companies to unravel the structure of underground reservoirs. 
Note that 10^5 Pa (ie 10^5 pascals) is a pressure of one atmosphere. So 80 x 10^5 Pa is a pressure of 80 atmospheres. For comparison, a car tyre commonly operates at a pressure of about 2 atmospheres.
Given Furnival’s quoted liquid CO2 density of 700 kg/cubic metre (ie 0.7 tonne/cubic metre), our hypothetical 5,000 cubic kilometre storage, conceived of for the moment as a ‘cave’, will hold around 3.5 x 10^12 tonnes of CO2.
The European Environment Agency’s latest report on GHG emissions is on the web . According to that EEA report, the 15 countries of the European Union as in 2004 had total GHG emissions of 4,227.4 million tonnes, not all of it, of course, from thermal power stations. The subsequent admission of eight central and eastern European nations plus Cyprus and Malta has pushed the total to 4,979.5 million tonnes for that year. That is, 5.0 gigatonnes when rounded. As that would require only 1/700 of the space in the ‘cave’, it leaves a lot of room for supporting rock as well. The CO2 will actually reside in pores in the rock, and note that for this purpose I have assumed that all the GHG is CO2. It would take 700 years to fill the ‘cave’ with Europe’s emissions at their present rate, provided it was a hollowed-out chamber.
So what about Nikki Williams claim about storing “Europe’s 600 billion tonnes of CO2 emissions for the next 600 years”? Well, 600 billion is 600,000,000,000, or 6.0 x 10^11 tonnes, and the empty ‘cave’ will hold 3.5 x 10^12 tonnes of CO2. The CO2 will take up 17% (nearly a fifth) of the room in it, which seems a lot of space for the interior of porous rock. Utsira has shown that it can take one million tonnes of CO2 produced in the adjacent oilfield in a year. However, this is dwarfed by the increase of emissions of greenhouse gases from the EU-25, which increase was by 18 million tonnes (0.4 %) between 2003 and 2004. Emissions from the EU-15 increased by 11.5 million tonnes (0.3 %) in the same period.  That is to say, the increase per year alone is eighteen times the mass of CO2 injected per year to date into the Utsira aquifer, which helpfully is in close proximity to the CO2 source: the Sleipner oilfield. Something like Utsira, although impressive in size, might be used for all of Norway’s future emissions, but not all of Europe’s. That would require a multitude of sequestration sites closer to the points of production.
Nikki Williams was not wrong, though she may have stretched it a bit. But her article calls forth not so much an argument over big numbers, as the reply: ‘should we bury carbon dioxide forever?’
For CCS to make a meaningful contribution to alleviating the CO2 problem, a number of conditions have to be met:
- The source of the CO2 has to be close enough to the burial site to make transport to it practical. Many sources require many short pipes to many sinks. Otherwise, a network of pipelines from many sources to a few sinks will be necessary. The longer the pipe network, the greater the potential risks, such as random leaks, and those deliberately brought about by vandals, saboteurs and terrorists. If such take place in densely populated areas the results can be disastrous, as CO2 gas is deadly in the quantities and transportation rates envisaged for CCS.
- The containment beds such as saline aquifers (eg Utsira) and disused oil and gas wells have to be gas tight.
- Some arrangement for dealing with future situations in which CO2 starts leaking out of the geological store has to be in place.
- Future drilling exploration and mining into layers underneath the CO2 store will become significantly more expensive and dangerous, or have to be foregone completely. The economic consequences of this, all other factors being constant, will be in proportion to the geological area covered by the CO2 store. This will likely be comparable to the geological area of the original coal and oil fields from which the carbon was taken. The horizontal dimensions of Utsira (500 km by 50 km, and just one of many fields) give some idea of it.
- The mass of liquid CO2 to be stored if the program is to be successful is huge: in the order of 3 times the total mass of coal in the world’s coal reserves (which as we have seen is 909 Gt). That is, if we assume that acidification of the ocean by CO2 has reached saturation level and crisis point in terms of its effects on corals and other basic life forms, and that the ocean literally cannot take it any more. That in turn means 3 x 909 Gt or 2,727 Gt of carbon dioxide have to be captured and stored in order to protect the ocean. That is, 2.727 x 10^12 tonnes.
- Then there is what I call the seismic hydraulic jack problem, of which more below.
Protecting the atmosphere would be about 100 times easier than protecting the ocean, if that was all we had to do. The mass of the Earth’s atmosphere is 5.14×10^18 kg, and the total mass of atmospheric carbon dioxide is 3.0×10^15 kg, or 3,000 Gt. [18.5] The concentration of CO2 in the atmosphere is increasing by 0.4% per year, because the natural sequestering systems cannot cope with the Earth’s total annual increase in CO2 production. So the amount that must be sequestered per year by other than natural means, just to hold the global atmospheric concentration constant, is 0.4% of 3,000 Gt or 1.2 x 10^10 tonnes, globally. When we write that out in longhand, it comes to 12,000,000,000 tonnes per year, or 33 million tonnes of CO2 per day.
Australia’s share of the task is no trifle either. In 2004-5 Australian total domestic energy consumption was 5,525 petajoules (PJ). [19.5] Of this, 41 % came from coal, 35% from oil, 19% from natural gas and 5% from renewables. 41% of 5,525 PJ is 2,265 PJ, which translates to 79 million tonnes of coal. If we assume this to be on average 70% carbon, that makes 55 million tones of coal, which burned to yield around 200 million tonnes of CO2 that year; around 560,000 tonnes per day: the mass that must be buried under Australia if locally-burnt coal is to contribute zero CO2 to the global atmosphere and ocean problems.
These are huge capture and storage problems in themselves. However, there are also problems with the whole feasibility of CCS, even if on an industrial scale it can handle the daily mass of CO2 involved. Note that CCS only has relevance at present to coal, which these days is generally burnt in a relatively few huge furnaces in such establishments as power stations and iron smelters. However, we have seen that the remaining coal reserves contain 79% of the fossil fuel carbon, the oil reserves 11%, and the natural gas reserves 10%. The world thus has around eight times as much coal reserves as it has of petroleum reserves, and four times as much carbon in the coal as in oil and natural gas combined. Carbon capture and storage is not applicable to most domestic and industrial uses of gas and petroleum fuel, so the future of captured carbon is largely the future of CO2 derived from the burning of coal. Such future devices as ‘plug in and charge’ automobiles, will run in on energy from coal unless renewables take its place.
Once a suitable site has been chosen, the mechanics of storing carbon dioxide are not too difficult – it just involves a few pipes, some injection wells and equipment to compress the carbon dioxide before it is stored. The main issue is to ensure that once injected, the carbon dioxide will not find its way back to the surface in any significant amounts. The most likely leak path is through wells, both active and abandoned. Furthermore, when water and carbon dioxide mix they form carbonic acid, so new sealing methods must be developed using cements that are resistant to this chemical attack. Long-term monitoring for leaks will be needed too – a responsibility that must be borne by governments since no commercial organization would take on such an open-ended commitment. While the lifespan of a typical oilfield is between 20 and 50 years, monitoring of CO2 leaks may be needed for millennia.
Here indeed is a major snag in the fine print of the contract. Potentially, it is the most outstanding example in all of economic history of what John Kenneth Galbraith called ‘privatised profits and socialised losses.’ Once Australia’s or any other country’s government allows its private CO2 emitters to start moving down the CCS path, it must accept total liability, literally from here to eternity, for anything which might go wrong. That includes the foreseeable, like leaks, and the unforeseeable, like literally God knows what. It would be a very brave actuary, working for an insurance company with very deep pockets and most charitable shareholders, who would even try to work out the statistics on that, let alone suggest an annual premium for that total liability.
So I have serious reservations about the whole business, and regard the $500 million earmarked in the last Australian budget for CCS as likely to be wasted. Although it will all finish up in certain peoples’ bank accounts, whether it will do any good as it makes its way into them is an open question.
The main disincentive to wide-scale adoption of CCS is the expense. It is estimated that CCS will cost between [US] $25 and $50 per tonne of CO2, of which 80% is the cost of capture. To get a feel for this, consider that each tonne of coal burned produces about three tonnes of CO2, and that a typical 1 GW coal-fired power station produces 6 million tonnes of CO2 per year. The energy required to operate an effective capture scheme at a power plant would therefore significantly reduce its operating efficiency. Although it should be possible to reduce the cost of CCS by 20–30% in the next decade, further savings will depend on the adoption of the technology together with on-going research and development. In the mean time, a tax on carbon-dioxide emissions would certainly make CCS more economically attractive…
A major concern when storing carbon dioxide in saline aquifers is that the natural seal at the top of the formation – a layer of non-porous rock – could be broken during CO2 injection. So far, this seal has remained intact at Utsira, but if it does eventually break, the hope is that a series of shallower seals will minimize the amount of carbon dioxide that will escape…
The probability of such escapes happening is likely to be a function of the mass of CO2 stored, the time stored, and the number of seismic movements per year, as measured over millenia.
Furthermore, it is believed that over a period of about 1000 years carbon dioxide will dissolve in the brine inside the aquifer, producing a CO2–brine mixture that is heavier than unsaturated brine. The saturated brine will thus move downwards, helping to lock the carbon dioxide away. Longer term still, on geological timescales, it is believed that chemical reactions will turn the CO2–brine mixture into a mineral, locking the carbon dioxide permanently into the Earth’s crust.
Reading through the above, we can see that there is far more faith and hope amongst CCS advocates than there is scientific certainty, which is understandable, as there is no such thing as absolute certainty in science. The dark horse in the race is seismic movement, and particularly the possible contribution of the massive and geologically extensive high-pressure liquid CO2 storage in the sedimentary layers below the Earth’s surface to the very same seismic movements that might give rise to such release. What the geosequestration wells will set up will be in reality an array of gigantic hydraulic jacks. The force exerted upwards on the overlying strata by the gigatonnes of sequestered liquid CO2 will be equal to about a third of the weight of the overlying strata. As we have seen, the CO2 will require a pressure in the order of 100 atmospheres to remain liquid in the temperature conditions found at a sequestration depth commonly around 1 kilometre below the surface. Deep wells are favoured because of the containment strength needed. But even in the deepest, the gas pressure could have a significant easing effect on the friction blocking relative movement of adjacent strata. Applied over the areas envisaged, this could be of seismic significance. Literally.
Admittedly, the gigantic ‘slave cylinders’ [19.55] of the jacks (ie the sequestration reservoirs below ground) will not have impervious walls, as those of normal hydraulic jacks do. The pressure in the liquid CO2 below will even out as water is displaced through the porous reservoir rock. A moment’s reflection shows that if the reservoirs were watertight, liquid CO2 could not be pumped into them in the first place, as liquids are incompressible. But of course, this raises the next question: where will this displaced CO2-plus-water mix finally end up? If it moves downward or horizontally, it could eventually find its way via a submarine outcrop of the aquifer into the ocean, and from there the CO2 component could return to the atmosphere. This may not necessarily be bad for the biosphere or humanity, provided it happened slowly enough.
Apart from the six problems with CCS listed above, there is a seventh, and far more major one. It may appear to be a long term problem, and therefore dismissible by politicians and others who only permit themselves to think in the short term. But it will phase itself in as the existing carbon economy is phased down and then out over the anticipated life of the present deposits of fossil carbon fuel.
7. Humanity cannot afford to bury the CO2 forever, because our descendants in the period of human historical time beyond the lifespan of the present fossil fuels (50 years for petroleum, perhaps 250 years for coal) will need the carbon. With high probability.250 years backwards in time takes us from 2008 to 1758: that is to the period around the start of the Industrial Revolution in Britain, when the Enlightenment foundations of much that distinguishes modern thinking from what preceded it were being laid, and the CO2 concentration of the atmosphere was just starting on its exponential trend upwards. Nineteen years on from 1758, James Cook would step ashore at Botany Bay. So it is not so far further on from this present point in human history before a decision today to close off the options of later generations could well be seen as one of the stupidest choices members of our species have ever made.
We should not “bury carbon dioxide forever”. It should only be buried, if at all, for as long as it takes to restore pre-1758 atmospheric CO2 concentrations, and should always be retrievable. The problem affecting the present atmosphere and ocean is the unprecedented rate at which CO2 is being added to them both.
We have unwittingly been running an experiment on the planet, and with only limited control of variables. With luck, it will yield data sufficient for future scientists to make reasonably confident predictions as to the effect of particular atmospheric CO2 concentrations on the global climate. We are, with Kyoto, embarking on our second attempt to actually control the climate of the whole world, by controlling the concentration of GHG. The first was the (moderately successful) attempt to patch the hole in the Ozone Layer by progressively banning chlorinated fluorocarbons from mass usage in refrigeration and other applications. At the Montreal Summit, on September 21, 2007, approximately 200 countries agreed to accelerate the elimination of hydrochlorofluorocarbons entirely by 2020. Developing nations were given until 2030. Many nations, such as the United States and China, which had previously resisted such efforts, agreed with the accelerated phase-out schedule. [19.555]
By holding all other factors constant in controlled environment experiments, plant physiologists have repeatedly shown that the carbon dioxide concentration in the air available to the plant is the major limiting factor on plant growth. Number  in the links and references list below is a report of but one typical experiment. It is likely that the plants of the biosphere will increase their rates of photosynthesis and growth as the concentration of atmospheric CO2 rises, provided global warming does not produce factors like drought and heat stress which drive them in the opposite direction. Eventually as fossil fuel reserves run down, and provided we do not pass a tipping point along the way and enter runaway greenhouse conditions, the CO2 will stop its rise in atmospheric concentration, peak, and then start trending downwards, as photosynthesis exceeds combustion and respiration combined. Other factors could well join in along that way to plunge the planet into a new ice age. The ability of the human population of the globe at that time to elect to stay out of such a development will likely depend on its having the ability to adjust the atmospheric CO2 concentration to suit itself. In those circumstances, a decision on the part of this generation to “bury carbon dioxide forever” and seal the captured carbon storage wells permanently after filling, would be seen as careless and short-sighted. So carbon geosequestration should always be carried out in such a way as to not cut off the option to retrieve the CO2 at a later date. The extent to which that can actually be done remains to be seen.
In 2000, the Dutch atmospheric chemist and Nobel prizewinner Paul Crutzen  coined the term Anthropocene for the period of geological time we are now living in. It appears to be catching on in the scientific community.   The preceding Holocene period began 10,000 years ago when the Pleistocene glaciers had retreated sufficiently to allow agriculture to begin. Argument now occurs as to when, if at all, it ended and the Anthropocene began. Crutzen says:
To assign a more specific date to the onset of the ‘Anthropocene’ seems somewhat arbitrary, but we propose the latter part of the 18th century, although we are aware that alternative proposals can be made (some may even want to include the entire Holocene). However, we choose this date because, during the past two centuries, the global effects of human activities have become clearly noticeable. This is the period when data retrieved from glacial ice cores show the beginning of a growth in the atmospheric concentrations of several ‘greenhouse gases’, in particular C02 and CH4. Such a starting date also coincides with James Watt’s invention of the steam engine in 1784. 
I like the term, but would argue that the period began very abruptly: on September 21, 2007, when the Montreal Protocol was signed, marking humanity’s first conscious step towards climate control of the whole planet. The Kyoto Protocol, which was adopted on 11 December 1997 and entered into force on 16 February 2005 was a second, and far more difficult advance. 
Carbon is presently being moved out of one of its major stores on our planet, the rocks, and into another, the atmosphere. Human civilization presently depends as heavily on the carbon stored in the lithosphere as it depends on what is in the biosphere. The plants are hardly benefiting from this transfer, particularly as the Earth warms as a result. Today it is no exaggeration to say that we are not only transported about the face of the Earth by petroleum and coal, we also eat it, drink it, wear it and shelter under it. (For example, roofing iron is galvanized steel, smelted from its ore using coal.) We will be able to continue in our present style of carbon dependence if, and only if, the lithosphere carbon is moved slowly and steadily into the biosphere. Otherwise, when the fossil fuels finally run out, the biosphere, operating on roughly its present carbon mass (plus what it gets from the CO2 from the burning of fossil fuels other than coal, which cannot be geosequestered) will have to carry the full load. Its carbon will have to supply all our carbon-based needs.
The geosequestrationist proposal is to bury the CO2 forever back into the rock of the lithosphere. The case I have been setting out in this document is that the greatest benefit would arguably come about if we gradually returned the planet to the pre-Carboniferous situation, before its largest ever carbon store transfer, which was from the biosphere to the lithosphere. A progressive transfer of the carbon coming out of the lithosphere back into the biosphere would involve, and in no small measure, the reafforestation of the globe. It was much more extensively forested in the Carboniferous and the Permian.
The plants will do that by themselves if we give them the time (say a few hundred years) and a bit of conscious assistance. Ecological successions of them could take back the Sahara, the Great Sandy, the Gobi, and most of the other deserts of the world.
The US Census Bureau has estimated that the world’s human population will be 9.4 billion by 2050.  It is 6.7 billion today.  By that time also, says the prevailing scientific consensus, GHG production will have to have been reduced to 50% or less of the 2000 level, and the atmosphere’s CO2 concentration stabilized. That is, if runaway global warming is to be avoided.
A CSIRO study published on July 11, 2008 predicts that by 2018, petrol in Australia will cost around $8.00 per litre. (The previous day, the CSIRO announced success in capturing CO2 in flue gases at Loy Yang Power Station, Victoria, with the experimental plant being capable of capturing 1,000 tonnes of CO2 per year, which is 2.7 tonnes per day. (!)) Thus as petroleum recedes over the next 40 years, crop plants of various kinds will be called upon increasingly to provide not just our food and fibre, but liquid fuels for transportation. Those 9.4 billion people of the year 2050 will need cotton for their clothes, wood for their housing, cooking and home heating, fodder for their livestock and crops of edible plants for themselves. They will also need fuels (most likely also derived from plants) not just for transport, but for a host of industrial purposes as well.
I do not think that it is a wise move to pump the CO2 that could feed all those future plants, and those dependent on them, irretrievably, permanently and forever into the depths of the Earth. Thus the inescapable conclusion is that any carbon capture and storage scheme of a magnitude sufficient to have a noticeable effect on global climate has to be done in a temporary, retrievable way. Cutbacks in global production of CO2 from the burning of coal will have to make up for any shortfalls in CCS, which on the face of it, promise to be significant. That in turn means cutbacks in the production of steel, electricity and cement where these use coal as fuel.
And that in turn will mean significant, if not huge, price increases for those commodities. The only alternative would be to let the Earth fry.
If carbon capture and storage is capable of any significant dampening effect on global warming, then the CO2 involved will inevitably be a resource of massive importance for the future inhabitants of the Earth. That in short, is the other side of the CO2 coin. Our present climate change situation compels us to perceive atmospheric CO2 only as a problem. We should be seeing it differently: as a short term problem, but despite that, as a longer term vital resource.
REFERENCES AND LINKS[0.5] http://www.thehistorychannel.co.uk/site/encyclopedia/article_show/Parthenon/m0012197.html
 http://en.wikipedia.org/wiki/Ocean (The total mass of the hydrosphere is about 1.4 × 1021 kilograms, which is about 0.023% of the Earth’s total mass. Less than 2% is freshwater; the rest is saltwater, mostly in the ocean.)
[5.25] Hoffman, PF and Schrag, DP, Snowball Earth, Scientific American, January 2000. http://www.amherst.edu/~jwhagadorn/courses/27paleo/readings/HoffmanSchrag2000.pdf
 John C. Walton, The Chemical Composition of the Earth’s Original Atmosphere. http://www.grisda.org/origins/03066.htm