Carbon Cycles and Sinks - The Case for Man Made Carbonate

Carbon Cycles

According to Wikipedia[1] "the carbon cycle is the bio-geochemical cycle by which carbon is exchanged between the biosphere, geosphere, hydrosphere, and atmosphere of the Earth....The cycle is usually thought of as four major reservoirs of carbon interconnected by pathways of exchange. The reservoirs are the atmosphere, the terrestrial biosphere (which usually includes freshwater systems and non-living organic material, such as soil carbon), the oceans (which includes dissolved inorganic carbon and living and non-living marine biota), and the sediments (which includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest active pool of carbon near the surface of the Earth, but the deep ocean part of this pool does not rapidly exchange with the atmosphere.

The global carbon budget is the balance of the exchanges (incomes and losses) of carbon between the carbon reservoirs or between one specific loop (e.g., atmosphere - biosphere) of the carbon cycle. An examination of the carbon budget of a pool or reservoir can provide information about whether the pool or reservoir is functioning as a source or sink for carbon dioxide."

The Global Carbon Cycle[2]

The Carbon Equation

The carbon equation describes the carbon cycle and an analysis leading to a summary equation follows.

According to Richard Haughton at the Wood's Hole Institute[3] "If the global totals for photosynthesis and respiration are not equal, carbon either accumulates on land or is released to the atmosphere. Unfortunately, the global rates of photosynthesis and respiration are neither known nor measured well enough to determine annual changes in carbon storage. On the other hand, human use of the land, for example the clearing of forests for croplands, is relatively well documented, both historically and with satellites, and thus can be used to determine changes in the storage of carbon. ...... much of the carbon stored in trees and soils is released to the atmosphere when forests are cleared and cultivated. Some of the release occurs rapidly with burning; some of it occurs slowly as dead plant material decomposes. When forests re grow on cleared land, they withdraw carbon from the atmosphere and store it again in trees and soils. The difference between the total amount of carbon released to the atmosphere and the total amount withdrawn from the atmosphere determines whether the land is a net source or sink for atmospheric carbon."

The Woods Hole Institute focus their research on the net emissions from changes in land use and consider the net emissions from this source to currently be around 2.2 billion tonnes per annum. Although there are various estimates for emissions from fossil fuels and for oceanic uptake, based on their research the Woods Hole Institute have assumed 6.5 and 2.4 billion tonnes respectively and derived the carbon equation below.

Atmospheric increase	=	Emissions from fossil fuels	+	Net emissions from changes in land use	-	Oceanic uptake	-	Missing carbon sink
3.2 (±0.2)	=	6.3 (±0.4)	+	2.2 (±0.8)	-	2.4 (±0.7)	-	2.9 (±1.1)

The Carbon Cycle in billion metric tonnes or petograms. [3][4]

Converting to tonnes CO2 in the same units by multiplying by 44.01/12.01, the ratio of the respective molecular weights.

Atmospheric increase	=	Emissions from fossil fuels	+	Net emissions from changes in land use	-	Oceanic uptake	-	Missing carbon sink
11.72 (±0.2)	=	23.08 (±0.4)	+	8.016 (±0.8)	-	8.79 (±0.7)	-	10.62 (±1.1)

The Carbon Dioxide Cycle in billion metric tonnes or petograms.

From the above the annual atmospheric increase of CO2 is in the order of 12 billion metric tonnes.

TecEco plan through Gaia Engineering to modify the carbon cycle by creating a new man made carbon sink in the built environment. The need for a new and very large sink can be appreciated by considering the balance sheet of global carbon in the crust after Ziock, H. J. and D. P. Harrison[5] depicted below.

Carbon Sinks and Anthropogenic Actual and Predicted Consumption of Carbon[5]

According to Ziock, H. J. and D. P. Harrison[5] "The size of natural carbon sinks or pools compared to fossil fuels reserves and to potential emissions in the new century. For emissions we show four blocks of 600 Gt each. 600 Gt would be the result of 100 years of constant emissions at the current rate. If the last century is any guide, the output could be five to six times larger. In the emission column below the zero line we show the far smaller total emissions of the 20th century, which in turn dwarfed the emissions of the 19th century. Individual blocks below the zero line represent 100 years of emission at the rate of 1900. The easily accessible carbon reservoirs with the exception of the ocean are comparable in size to the expected emissions of the next century. However, one would be hard pressed to actually double the existing biomass without substantively changing the environment. The ocean reservoir, at 39,000 Gt of carbon, is far larger, but its ability to take up carbon without environmental change is limited. Above the zero line, we are showing the amount of carbon that when dissolved in the ocean in the form of CO2 would change its pH from top to bottom by 0.3. .....The resource columns show that available fossil energy exceeds all likely demand for at least a century or two."

If a proportion of the built environment were man made carbonate, how much would we need to reverse global warming?

MgO + H2O => Mg(OH)2 + CO2 + 2H2O => MgCO3.3H2O
40.31 + 18(l) => 58.31 + 44.01(g) + 2 X 18(l) => 138.368 molar masses.
44.01 parts by mass of CO2 ~= 138.368 parts by mass MgCO3.3H2O
1 ~= 138.368/44.01= 3.144
12 billion tonnes CO2 ~= 37.728 billion tonnes of nesquehonite or

MgO + H2O => Mg(OH)2 + CO2 + 2H2O => MgCO3
40.31 + 18(l) => 58.31 + 44.01(g) + 2 X 18(l) => 84.32 molar masses.
CO2 ~= MgCO3
44.01 parts by mass of CO2 ~= 84.32 parts by mass MgCO3
1 ~= 84.32/44.01= 1.9159
12 billion tonnes CO2 ~= 22.99 billion tonnes magnesite

The density of magnesite is 3 gm/cm3 or 3 tonne/metre3

Thus 22.9/3 billion cubic metres ~= 7.63 cubic kilometres of magnesite

CaO + H2O => Ca(OH)2 + CO2 + 2H2O => CaCO3
56.08 + 18(l) => 74.08 + 44.01(g) + 2 X 18(l) => 100.09 molar masses.
CO2 ~= CaCO3
44.01 parts by mass of CO2 ~= 100.09 parts by mass MgCO3
1 ~= 100.09/44.01= 2.274
12 billion tonnes CO2 ~= 27.29 billion tonnes calcite (limestone)

The density of calcite is 2.71 gm/cm3 or 2.71 tonne/metre3

Thus 27.29/2.71 billion cubic metres ~= 10.07 cubic kilometres of limestone

How do these numbers compare with world production of concrete, bricks, mud bricks, tiles and other mineral based building materials?

Global figures are very scarce and when available inaccurate for mineral based building materials other than cement and concrete for which reasonably good statistics are available from the USGS[6]. Nevertheless we will try and derive a figure for mud and clay bricks, the next most dominant materials.

According to the Australian Bureau of Statistics (ABS) that countries production of clay bricks during 2007 (the latest figures as at the date of writing) was 1459 million[7]. At approximately 2.5 Kg each on average this equates to 3647 thousand tonne. Again according to the ABS Australian cement production for 2007 was 9839 thousand tonnes and for concrete 26593 thousand cubic metres[7]. At 2.4 tonnes to the cubic metre concrete production in Australia calculates to 63823 thousand tonnes. As Australia in terms of GDP is about .0172 as a fraction of global GDP[8], calculation gives the global figures as 3647/.0172 = 212063 thousand tonnes for bricks and 3710639 thousand tonnes for concrete.

The global statistics for cement and concrete are easier to obtain and considerably more accurate. The data in the graph below is from the USGS Minerals Year Book for Cement[6] and calculated for concrete assuming it contains on average 12% cement[9].

World Production of Cement and Concrete [6]

The global figure we have derived for clay bricks based on Australian production is an underestimate because in third world and poorer countries their use exceeds that of concrete whereas in Australia, the US and other OECD countries concrete is the dominant construction material. This also explains why derivation of a global figure from Australian production of concrete is an overestimate.

The only mineral flow in the world that rivals concrete is that of mud brick. About half of the inhabitants of the earth build with local natural materials and mud brick is at the top of the list.

Conclusion

Taking into accounts clay bricks, mud bricks and all other mineral based building materials including stone it is reasonable to assume the total flow of mineral based building materials to he about double that of concrete at around 50 billion tonnes. Other building products are about half as much again so total building materials flows are in the order of 75 billion tonnes.

From our studies of the carbon cycle and carbon equation we concluded we need to put about 23 billion tonnes of magnesium carbonate away annually to solve the problem of global warming. It follows that if magnesite or for that matter any carbonate that was man made was our building material of choice and we could make it without releases we would have the problem of global warming well on the way to being solved!

Our claim that if half of all building and construction was using man made carbonate then the problem would go away by 2025 is looking good, especially if accompanied by the development of alternatives to fossil fuels. Modeling from a different route but that confirms the same conclusion is available from the TecEco web site[10].

In the Gaia Engineering technical paradigm TecEco plan to make composites in which the aggregate and cement that binds them are both man made carbonate. Please help us on this great endeavour.

 

 

printer friendly

Menu