[SustainableTompkins] Avoiding the GHG tipping point

[bosak at ibiblio.org]

Thanks, Marty.  Exactly what I was looking for.

Jon

> 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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>
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