1We all know about the role of carbon dioxide in causing global warming.
2Obviously, society needs to reduce the release of carbon dioxide, otherwise known as CO2.
3This gas comes from the burning of fossil fuels, such as coal and oil,
4and it is virtually impossible for society to prevent, or even limit such activity.
5Our need for energy and power is just too great.
6Instead, a more practical idea is to collect the carbon dioxide from the burning process,
7for example, directly from the chimneys of power stations,
8and somehow prevent this gas from being released into the environment.
9To do that, you need to store it somehow, and that has to be essentially forever.
10It is perhaps for this reason that many believe that,
11rather than storing the carbon dioxide as a gas,
12it is better to react it with metal oxides, such as magnesium or calcium,
13which results in the formation of a hard carbonate material.
14The gas is, in effect, turned into a stable and unreactive solid,
15which can simply be dumped anywhere.
16This process actually occurs naturally, although very very slowly,
17and is one cause of the surface limestone in the world.
18But this slow reaction speed is the problem.
19Even when enhancing this process through high temperature and pressure,
20or pre-treatment of the mineral, it is still far too slow to be economical.
21One other technique which has been suggested is to pump the gas to the bottom of the ocean,
22where it would react with compounds in the seawater, forming carbonic acid.
23However, this alternative has now been ruled out.
24The CO2 may be removed from the atmosphere,
25but the high oceanic acidity which would result raises its own set of problems,
26mostly with all the delicate life and the intricate food chains in the seawater,
27some on which we ourselves depend,
28and that's something which no one wants to experiment with.
29Perhaps because of the lack of alternatives,
30the most commonly discussed solution to the problem of disposing of carbon dioxide is to pump the gas underground -
31a technique known as 'geosequestration'.
32In this system, the CO2, for example,
33could be pumped into underground pockets within depleted oil wells, or disused coal tunnels.
34This carries, however, three serious disadvantages,
35namely: the risk of leaks, the considerable costs involved,
36and finally, the unproven effectiveness.
37Let us look at those three disadvantages in detail.
38Firstly, there is the risk of leaks.
39Although the gas would be deep and sealed over by masses of rock and earth,
40the huge pressures in these spaces would turn the gas into a liquid state
41capable of moving through rock fissures or faults.
42This could allow the gas to eventually be released to the surface.
43Since CO2 is heavier than air,
44and thus pushes oxygen aside,
45such leaks could result in the suffocation of thousands, or tens of thousands of people -
46certainly not a consequence to be taken lightly.
47Natural CO2 leakage from volcanic build-up has already witnessed such deadly events.
48The other problem of geosequestration is the cost.
49The time and effort spent on materials and construction,
50primarily the pipework through which the gas would travel, does not come cheaply.
51So, if this system were to be implemented in, say, coal-fired power plants,
52the extra cost would have to be paid by the electricity user,
53whose bills would almost double as a consequence.
54Few people are prepared to pay this much simply to make a small dent on the effects of global warming.
55And this leads to the final problem.
56The most basic question is whether geosequestration actually reduces global warming.
57The problem here is that the energy needed to create
58and drive the sequestration process would require approximately
59a quarter of a coal-fired electricity plant's output.
60In other words, the plant would have to burn one quarter more of its coal
61just to account for the sequestration of the carbon dioxide,
62and with coal producing other noxious pollutants,
63such as sulphur, ash, and heavy metals,
64the environment is hardly benefited at all.
65Nevertheless, there are many active experimental efforts underway,
66primarily in oil production sites.
67These are small but intensively monitored and analysed.
68All we can say now is that the jury is still out on whether underground carbon storage will one day be feasible.