Hi all I can write with all the authority of someone who has made a great many arithmetical mistakes and has learned painfully that when you are dealing with big numbers in a new field it helps to stay in base units for as long as possible and to make many small steps which are easily checked. I offer the following bit of MathCad.
Stephen Emeritus Professor of Engineering Design School of Engineering and Electronics University of Edinburgh Mayfield Road Edinburgh EH9 3JL Scotland tel +44 131 650 5704 fax +44 131 650 5702 Mobile 07795 203 195 [email protected] http://www.see.ed.ac.uk/~shs Peter Read wrote: > Re > "RWL: Ken is speaking here to Stephen Salter's grazing land estimate of > 5E15 m2, which (I agree) seems to be a factor of 100 too large (because > there are 100 ha in a sq km??)" > And > (Ken)" Therefore, we will need about 1.2 * 10^14 m2 or the same order of > magnitude as all of the land in the world." > > Let's get the notation straight (and I might be wrong as it is sometime > since I was instructed) > But YeX means Y times 10 raised to the power of X (OK??**) > So, for example 1.4e2 means 140 > Using "^" to mean "raised to the power of" > Then there are 1e4 m^2 per Ha (and 1e2Ha per Km^2 hence 1e6 m^2 per > Km^2 ) > [[ which seems OK given that K means 1^3 and 1^3 x 1^3 = 1^6 ]] > > It is tiresome that GigaHectares (GHa), or billions of Hectares, which > are > usually used in working with global land areas, embody the 1e4 factor > of Ha > relative to m^2, but that's how it is > Giga means 1e9 so a GHa is 1e13 m^2 > According to Wiki global land area is 148,940,000 Km^2 = > 14,894,000,000 Ha > or ~15 Gha = 1.5e14 m^2 > > So grazing and pasture broadly interpreted as about one third of that is > 5e13 m^2 > Looks as though Ken is out by a factor of 10 and Lovell Ward quoted by > Stephen by 100 > > I strongly recommend GHa since, as there are only 15 of them, a mental > reality check is not too difficult > > Re Ken's : "Normal ecosystem efficiencies are typically around 0.5 %. > If we > assume average sunlight at ground at 200 W/ m2, we get 1 W/m2 ecosystem > rates of producing reduced carbon." > > Net global terrestrial fixation of ~60GtC/yr. = ~ 120Gt dry biomass/yr = > ~1800 EJ/yr at 15GJ/t dry biomass = 1.8e21(J/yr)/3e7(seconds/yr)=0.6e14W. > 0.6e14W/1.5e14m^2 = 0.4W/m^2 = 0.2 per cent of 200. As I said before, > nature doesn't do very well > > Normal management of eucalypt forestry in well watered tropical > regions gets > 25 dry biomass tons/Ha /yr or 400GJ/Ha yr (I believe 80 dry tons/Ha-yr is > the record with a bit of TLC at research establishments in Brazil). > 400e9J/ha-yr)/(1e4m^2/Ha*3e7 seconds/yr) = ~1.3W/m^2 > (Not 0.4 -- as I said before, nature doesn't do very well). With a > bit of learning by doing we can likely get it up to 2W/m^2 > > 2Gha*400GJ/Ha-yr = 800EJ/yr cf global commercial energy demand of about > 500EJ/yr > Which 2GHa?. Well Len Ornstein has given us 1.6GHa of irrigated desert > (maybe use the spare 300 EJ to pump the desalinated water up) > Maybe pump salt water up and let evaporation do the trick as suggested > recently, then recuperating some of the energy as the brine flows back > to sea level > And there's that 5Gha of grassland though I guess some of that is > near-desert and we mustn't double count > > Yes Ken, these things look pretty stupendous. But facing up to > dealing with excess CO2 in the cheapest way available (growing trees, > and later running a biofuel economy) makes one realize how silly it is > to try to fix the problem by costly emissions reductions. Remember, > Ornstein's desalination and irrigation , stupendous though it seems, > is cheaper than CCS (though I'm sure CCS has an important role to > play). Putting 330Gt C into the atmosphere-ocean over the last 2 > centuries has left us with a stupendous problem > > Simon > re "- Peter, in discussing the numbers you said of agricultural wastes > "If > the lot were pyrolyzed" which strikes me as a pretty big if. " > Yes of course. I was merely showing that there is a lot of it about > even before we start growing more. I would like to see it put into a > biodigester to extract methane for on the farm/village scale use, then > some residue pyrolyzed for char and more energy and then mixed with > the rest of the digester residue to put back on the land. But no doubt > others will have better ideas - more research, but that does not mean > delaying doing good for want of knowing how to do best > > Peter > > PS **Beginning to feel a bit nervous about all this I again resort to > Wiki > to > find > ""Most calculators and many computer programs present very large and very > small results in scientific notation. Because superscripted exponents > like > 10^7 cannot always be conveniently represented on computers, > typewriters and > calculators, an alternative format is often used: the letter E or e > represents times ten raised to the power, thus replacing the x 10n. "" > OK?? > > > ----- Original Message ----- From: "Ron Larson" > <[email protected]> > To: <[email protected]> > Cc: "Stephen Salter" <[email protected]>; "Manu Sharma" > <[email protected]>; "Peter Read" <[email protected]>; > <[email protected]>; "geoengineering" <[email protected]>; > <[email protected]>; <[email protected]> > Sent: Monday, September 28, 2009 5:37 PM > Subject: Re: [geo] Re: Grass root answer to Ken's question > > [[snipped - PR]] > > -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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