[SustainableTompkins] Avoiding the GHG tipping point

[Marty Hiller]

Hi Jon,
Here's a graphic: http://www.grida.no/climate/vital/13.htm

which shows us adding about 5.5 GT carbon from fossil fuels and the 
oceans sequestering about 2 GT carbon each year, which implies that we 
should reach a net zero increase if we drop our emissions from 5.5 to 
2, which is about a 65% reduction. Obviously it's a lot more 
complicated than that, but it'll do for a back-of-the-envelope 
calculation.

If you assume we have 20 years at our current usage (which is one 
heckuva big assumption,) a 2% per year reduction would buy us an extra 
15 years, and a 3% per year reduction for 35 years would keep us below 
the tipping point. Our releases are currently increasing by a bit over 
2% per year, if I recall correctly, so with business as usual we would 
have about 15 years, not 20.

If we assume it takes five years to reach global consensus, we'd have 
to up the reduction rate to about 4% per year to back us out of those 
five years of growth.

- Marty


On Oct 5, 2006, at 12:33 PM, bosak at ibiblio.org wrote:

> A scientific opinion widely quoted recently is that we will reach
> a "tipping point" where climate change becomes irreversible when
> the atmospheric concentration of CO2 reaches 440 ppm.  (We're
> currently at about 382 ppm and at present rates of increase will
> hit the 440 mark in about twenty years.)
>
> It should be obvious that there are a lot of problems with setting
> a specific figure like this, but it's useful in trying to
> understand the situation.
>
> What I want to know is, by what percentage would current world
> consumption of fossil fuels have to decrease in order to avoid
> hitting the tipping point?  There would appear to be a lot of
> hysteresis (i.e., time lag) involved, so the amount of reduction
> would have to be more than the amount needed to maintain a steady
> state once we got there, but how much is that?  Fifty percent?
> Sixty?  Eighty?
>
> Has anyone crunched the numbers on this?  For purposes of
> discussion, I need just one credible, conservative estimate of the
> amount we'd have to reduce global fossil fuel consumption,
> starting today, in order to avoid hitting 440 ppm.  (It would be
> best to have several estimates, since they're bound to differ
> depending on methodology used, but I'd be happy to have just one.)
>
> Jon
>
>
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