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]] --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
