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SUMMER 2003 - The Moving Finger

Science musings from a desktop in West Oxfordshire

Lest Sleeping Giants Rise...

In the early 1950s a diffident, Birmingham-born writer of pulp-science fiction changed genres, in the process terrifying a world still traumatised by the horror of the Second World War with his vision of giant man-eating vegetables bent on world domination and simultaneously propelling himself to literary stardom. John Wyndham was to his generation what Michael Crichton is to ours, a novelist of incredible vision and meticulous research who enthralled his audience with scientifically accurate thrillers. And then in 1953 Wyndham capped ‘The Day of the Triffids’ with another landmark novel which was every bit as terrifying. ‘The Kraken Wakes’, is a novel of interplanetary invasion, with a difference, for the intruders (never identified and only glimpsed at the end of the book) colonise the depths of the oceans. Eventually their plan becomes clear; in an extravagant display of interplanetary compulsory-purchase they are melting the polar ice caps with a view to extending their preferred habitat onto the continents!

At the time Wyndham wrote this there was no indication that the human race was already engaged in an unwitting experiment to melt the polar ice caps by pumping CO2 and other greenhouse gases into the atmosphere. But today, at the start of the 21st century it is clear that unless we do something to curb the amount of CO2 going into the atmosphere we will be responsible for altering the Earth’s climate and melting the ice-caps with attendant sea level rise. Today estimates suggest that melting the Greenland and West Antarctic Ice sheet would contribute to a rise of global sea level by 5m each and that melting the massive East Antarctic Ice sheet would raise sea level by a colossal 70 metres. Of the three ice sheets the West Antarctic Ice sheet is already in a particularly unstable configuration so the prospect of a 5 metre rise in sea level – which may not sound much until one considers how much of the world’s population lives at or near sea level – is very real.

So what can we do? Is it enough just to cut down on carbon emissions? Almost certainly not, especially with the American oil lobby preventing the world’s most conspicuous consumer of energy (and therefore producer of carbon dioxide) from joining the Kyoto agreement. And it is very unlikely that a Third World desperate to join the First is going to react well to the idea that they cannot exploit their own coal reserves (the worst CO2 culprit), especially after our own two century history of profligacy. So we must face the fact that China, India, South Africa and others are all going to be burning coal for the foreseeable future. This is not to say that incentives to reduce carbon emissions are not going to be required – they very clearly are - and will probably take the form of some kind of carbon tax. The more CO2 you produce the more tax you will have to pay.

But a carbon tax is going to have to be backed up with some heavy duty science and technology to actually stop CO2 from entering the atmosphere. We are going to have to actually dispose of carbon as safely as we dispose of nuclear waste, and the clock is ticking. This process falls into two parts: extracting the CO2 at the point of production (‘capture’), and storing it somewhere safe (‘sequestration’).

Of the two the ‘capture’ part is more complex and more expensive. To retrofit CO2 scrubbers – such as those based on a mono-ethanolamine catalyst – is not practical for small emitters (e.g. cars and houses) and in even large plants would not be cost effective unless the CO2 is concentrated, which is not the case for fuels burned in air. Estimates suggest that in a typical 500-MW coal-fired power station at least a fifth of that energy would need to be expended on the capture process, a figure that makes the attempt unviable.

A more realistic idea is to change the way electricity generating equipment does the job in the future. An attractive idea is the ‘Integrated Gasifier Combined Cycle’ approach. This is based on ‘steam reformation’, where a conventional carbon-based fuel like natural gas is reacted with oxygen and steam before combustion yielding carbon monoxide and hydrogen. These two gases can be separated easily and the inflammable hydrogen easily utilised in, for example, a gas turbine. Mixing the carbon monoxide with more steam in the presence of a suitable catalyst yields CO2 and more hydrogen. Once again the hydrogen can be burned and the CO2 captured in preparation for sequestration. Proponents of the so-called ‘hydrogen economy’ love this idea.

So much for capture, but how is the carbon to be sequestered? There are several proposals; some more fanciful than others. In the latter category is the idea of infecting coral reefs with genetically engineered algae whose turbo-charged chloroplasts would gobble CO2 at enhanced rates. This is about as realistic as manufacturing Triffids to consume the CO2 – especially with so many reef ecosystems around the world already in such jeopardy from pollution and development. And yet, like John Wyndham’s peerless science fiction, such an idea has a basis in fact. Recently a serious proposal has been put forward to seed the ocean with iron to enhance the growth-rate of existing algae in the photic zone and draw down CO2 in this way. Studies have shown that iron is often a limiting nutrient in many parts of the world’s oceans and that seeding these areas with additional iron can increase local algal biomass enough to make the ocean itself change colour. Of course ‘green’ activists love the idea of growing more trees to store the additional CO2 but this is not practical because the carbon storage capacity of land-based ecosystems is tiny besides, for example, the storage capacity of the deep ocean.

This leads us to another strategy, which is to directly inject CO2 into the ocean at depths where it will not degas into the atmosphere for millennia. The ocean is by far the largest carbon sink on the planet and there are good reasons for thinking that it can be persuaded to take more. It is now well understood that CO2 flux to and from the oceans is intimately linked to the control of glacial-interglacial cycles; during glacial stages atmospheric CO2 is diminished while the CO2 content of the deep ocean is enhanced and during interglacials the reverse applies. However the precise mechanism and timescales on which the switchover occurs is the subject of intense and ongoing research.
Abyss

Both the deep ocean injection techniques under consideration involve extracting CO2 from waste gases and liquefying it by compression. In the simpler of the two variants this liquid CO2 is sprayed into the ocean at depths of over 800 metres. The bubbles of CO2 then dissolve before they can reach the surface and the subsequent, dense, gas-rich water will sink to the bottom where it eventually pools in the deepest parts of the abyss. Recently an international team based in Hawaii – the Pacific International Centre for High Technology Research - were set to try the CO2 injection experiment. But environmental protest groups in the islands objected on the grounds that the experiment would acidify local fishing grounds. The group moved to Norway (the home of the original idea) where the experiment was set to take place this summer on a reduced scale in the Norwegian Sea. Here too environmental protest groups successfully derailed the experiment so the future of the idea is now uncertain.

The objections to the deep ocean direct CO2 injection idea are based on the fact that the metabolic rates of deep-marine animals and microbes can be up to three orders of magnitude slower than in their shallow water cousins. This is a consequence of the low rate of food supply in the deep ocean and the fact that the fast reactions needed for prey capture in the sunlit world are not required in the abyss. A consequence of this sluggish metabolism is unusual sensitivity to CO2 because intracellular pH regulation mechanisms occur more slowly. CO2 crossing the cell membrane is hydrated to carbonic acid and because of this sluggish metabolism tends to linger rather than being disposed of rapidly. In macro-invertebrates and vertebrates reduced blood pH decreases the affinity of respiratory proteins (like haemoglobin) for oxygen. It is conceivable therefore that injecting CO2 into the deep ocean could result in the suffocation of deep dwelling species.

An additional hazard of increasing marine acidity has recently been highlighted by a joint study between Cambridge University and MIT. Work there has shown that the post-industrial revolution increase in marine CO2 has started to hamper the ability of carbonate secreting marine organisms (which live in the shallow waters at or near the photic zone) to build their shells. This is worrying for marine carbonates produced by the action of foraminifera (single-celled protozoans related to Amoeba) and coccolithophores (single-celled carbonate secreting algae) are a major natural sink of atmospheric CO2.

Another variant on the deep ocean direct CO2 injection idea is to inject the CO2 at even greater depths where the carbon dioxide will form CO2-hydrates. Peter Brewer of the Moss Landing Monterey Bay Aquarium and his associates have successfully induced CO2-hydrate formation at depths greater than 3 km. At such depths CO2 hydrates are metastable; as long as the pressure and temperature remain unaltered they will remain in this state for ever. Brewer believes that CO2 from power plants could be piped directly to the deep sea at the appropriate water depth where it will remain indefinitely in hydrate form and thus not contribute to global warming. Of course such an approach is still experimental and there is much work yet to be done. But even if the idea is sound there remains the question of whether we should do it. If there is one thing that we have learned from the legacy of the sea floor’s fossil record – and particularly the methane hydrates that explosively degassed at the Palaeocene/Eocene boundary (see Chemistry in Britain, May 2002) - it is that hydrates are very sensitive to quite small changes in temperature and pressure. Putting them on the sea-floor where periodic earthquakes and volcanic activity could destabilise them may not be wise.
Cameroon

In 1986 80 million cubic metres of volcanically derived CO2 gas dissolved in the bottom waters of Lake Nyos in Cameroon vented to the surface and asphyxiated 17,000 residents and countless livestock. The accidental dissociation of potentially huge amounts of industrial CO2-hydrate stored on the sea bed is probably only a matter of time and statistics and the consequences unimaginable. Also, the venting of the methane hydrates at the Palaeocene-Eocene boundary had severe climatic consequences, raising global sea and atmospheric temperatures by over 8oC in less than a thousand years. It is quite possible that accidental dissociation of artificial CO2-hydrate stores could have similar consequences. Given the risks, protection of such stores from more pro-active forces could also be a problem and artificial CO2-hydrate reservoirs would probably require protection on the order of that of a nuclear waste reprocessing facility.

So is there anywhere else to store our unwanted CO2? Another idea is to pump waste CO2 into disused or failing oil and gas reservoirs. Advantages are that the reservoirs are likely to be safe - after all they have already demonstrated their long-term ability to trap gases and fluids. Also, injection of pressurized CO2 is already widely used in the oil industry to enhance hydrocarbon recovery, especially in the United States. If this approach were more widely applied then more countries would benefit from this ability to kill two birds with one stone – storing CO2 and squeezing every last drop from failing hydrocarbon fields.
Sleipner

A similar approach has been pioneered by the Norwegian Oil Company Statoil since 1996. They have been engaged in an experiment to test the feasibility of reservoir storage, pumping CO2 into a water-bearing sandstone layer known as the Utsira formation beneath its giant Sleipner gas fields. In this deep saline aquifer the CO2 becomes absorbed into the water within two or three years in the same way that CO2 dissolves in mineral water. It is hoped that localised chemical reactions will also cause some of the CO2 to form carbonates and bicarbonates that would remain stable for millennia. The Utsira formation currently holds four million tonnes of CO2 and there is plenty of room for more. Estimates suggest that the sandstone, which is capped by an impermeable shale layer, could hold three years worth of CO2 emissions from all the power stations in Europe put together. It is a cost effective exercise for Statoil too, for by storing the CO2 in this way they are saving themselves Norway’s hefty $38 a tonne carbon tax. They expect to recoup their $80 million investment within two years.

The idea of using old oil wells has also been extended to old coal seams. The idea is that the CO2 would become trapped by absorption onto the surface of the coal. And, in a similar fashion to the oil wells, injecting CO2 might displace combustible methane and help the scheme pay for itself.

All of these technologies and others currently undreamt of are likely to be needed as we battle to control CO2 induced Greenhouse warming and consequent sea level rise. The danger is real, imminent, and must be faced lest Wyndham’s terrifying scenario become self-inflicted. To illustrate the menace that lurks in the deep Wyndham quoted Tennyson, and we can do no better;

Below the thunders of the upper deep,

Far, far beneath in the abysmal sea,

His ancient, dreamless, uninvaded sleep,

The Kraken Sleepeth…

SPRING 2003
WINTER 2002
SUMMER 2002

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Richard Corfield 2003 in association with pedalo.co.uk