From: kym@kymhorsell.com   
      
   Peter Percival  wrote:   
   > R Kym Horsell wrote:   
   >> Peter Percival  wrote:   
   >>> R Kym Horsell wrote:   
   >>>> Peter Percival  wrote:   
   >>>>> One hears about the degree to which airlines, shipping, cattle   
   >>>>> farming,... are contributing to greenhouse gases and thus to global   
   >>>>> warming.  How much do humans contribute by exhaling?   
   >>>>   
   >>>> Carbon comes in several forms call "isotopes".   
   >>>> Some isotopes indicate the carbon has come from underground and   
   >>>> out of contact with the environment for millions of years.   
   >>>> Some isotopes indicate they have come from a biological source   
   >>>> recently.   
   >>>>   
   >>>> Scientists can look at the carbon in CO2 and determine that the   
   >>>> extra carbon dioxide in the atmosphere that has accumulated significantly   
   >>>> since the 1850s (roughly 1600 Gt) is almost all from a source that was   
   >>>> biological yet out of contact with the enviornment for millions of years.   
   >>>>   
   >>>> Moreover the amount of extra CO2 in the atm roughly corresponds   
   >>>> with about 1/2 the total coal and oil burned in the past 150 years.   
   >>>> The other 1/2 has apparently ended up in the oceans where it has   
   >>>> decreased the pH by around .3 points.   
   >>>>   
   >>>> Google and highschool science is your friend.   
   >>>   
   >>> It maybe that my question was not clearly worded.  My apologies if   
   >>> that's so.  I'll try again.  One hears that cattle farming, for example,   
   >>> puts so many tonnes of CO_2 into the atmosphere annually.  Or it may be   
   >>> that cattle contribute such-and-such a percentage of all emissions.   
   >>> What I'm asking for is the numbers for humans: so many tonnes per annum   
   >>> or such such-and-such a percentage of all emissions.  Get it?   
   >> ...   
   >>   
   >> The wording was as clear as the underlying assumptions.   
   >>   
   >> But as indicated breath is not a human emission. Emissions accumulate   
   >> in the atm and it seems human-breathed-out-CO2 does not.   
   >   
   > I didn't know that!  What becomes of it?   
      
   It has a short pre history of being atm CO2.   
      
   Plants eat CO2.   
   Cows eat plants.   
   Humans eat cows.   
   Humans emit CO2.   
      
   If you are sufficient at data analysis you can get a reasonable   
   estimate of the length of the loop.   
      
   Henc we have for CO2 flagged with "natural" isotope ratios:   
      
     Plants eat 1kg of CO2 in 24 hrs.   
     ...   
     Human emits 1 kg of CO2 in 24 hrs.   
     Net addition to atm == 0.   
      
      
   But for "low C13/zero C13" flagged CO2 we have:   
      
     Human digs up 1 kg of coal in 24 hrs and burns it.   
     Net addition to atm == 1 kg.   
      
   Given coal and oil has 0 carbon C14 and even smaller than usual amount of   
   C13 we expect to see the amounts of C13 and C14 in the atm decline  over   
   time the more coal and oil is dug up and burned.   
      
   See relevant plots from e.g. Scripps for how that's going.   
      
      
   >> Calculating a percentage then makes as much sense as what   
   >> is the fraction of 5 apples from 10 oranges.   
   >>   
   >> If you want to calculate the number of Gt then take the amount of   
   >> CO2 breathed out by a single human in 1 year, multiply by 7 billion   
   >> and divide by around 2 to allow for the range in sizes.   
   >>   
   >> Google and a calculator are your friends.   
   >>   
   >   
      
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