Again, the level and expense of the atmospheric carbon drawdown required to
avert catastrophe and restore planetary energy balance will depend, in part, on present
and future emissions, so that relevant decisions remain in significant part within the
control of the targets of your present investigation.
Relevant to those necessary decisions then, as indicated in Exh. B at 13-15, if
emissions reductions of 6%, on an exponential basis, commence (at long last) in the year
2021, then the requirement to extract atmospheric carbon in order to avert catastrophic
climate change will be ~153 PgC. If, however, emissions do not steeply decline but,
instead, remain at their present level, then the carbon extraction required grows to ~695
PgC. And if emissions grow at a rate of 2% per year (“modestly slower than the 2.6 %yr-1
growth of 2000–2015” – see Exh. B at 12) then ~1630 PgC extraction will be needed to
reach the level of <350ppm atmospheric CO2 by 2100.
In terms of necessary expense, as denoted above we analyzed only the range of
cost estimates for extraction requirements above the ~ 100 PgC that we estimated could
be stored through improved forestry and agricultural practices. Id. at 15. Accordingly, if
global emissions reductions of 6% commence in 2021, then an additional ~53 PgC by
way of “technological extraction” would be required in order to return atmospheric CO2
concentration to < 350 ppm, and thus potentially avert catastrophic warming. Our
estimated cost for this level of extraction of this is $8-18 trillion, or $100-230 billion per
year if spread evenly over 80 years.
available at
http://www.precisrcm.com/DFID_Philippines_Reporting/Philippines_Sea_Level_Report
_Oct_2016.pdf, and Rietbroeka et at., Revisiting the contemporary sea-level budget on
global and regional scales, Proceedings of the National Academy of Sciences (Feb. 9,
2016) available at www.pnas.org/cgi/doi/10.1073/pnas.1519132113
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