From: peterxpercival@hotmail.com   
      
   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?   
      
   > 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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