but also a drawdown of excess CO2 from the atmosphere -- so as to reduce atmospheric CO2 to < 350ppm within a century -- and we suggest a range of answers to the critical question, How much carbon4 must be drawn down from the atmosphere to restore earth’s energy balance (and how much will that cost)? There is not one single answer set to that compound question, in part because the drawdown requirement is a function of both historic and future emissions and thus depends on whether fossil fuel CO2 emissions continue at a high, constant, or declining rate. Moreover, there is a considerable range of estimated costs for significant carbon drawdown. In Exhibit B to this submission, at pages 10-16, my colleagues and I attempt to specify that range. I should note first, that, along with a different, albeit partly overlapping set of colleagues -- including leading economists as well as leading climate scientists -- I had previously determined that, had emissions declined, on an exponential basis, by 6 % yr-1, commencing in 2013, then a total atmospheric drawdown, over several decades, of approximately ~100 PgC should have sufficed to return atmospheric CO2 to <350ppm, and thus press global temperature back to the range of the Holocene period. See Dangerous Climate Change (ref. at nte 1, supra) at 10.5 We anticipated that a drawdown of ~100 PgC could be achieved through reasonably natural means, including through reforestation and improved agricultural practices, wherein such efforts also would secure 4 It is important to note that a ton of atmosphere carbon reflects 3.67 tons of carbon dioxide, so that when my colleagues and I calculate, for example, that a total atmospheric drawdown of ~100 PgC was required under a certain emissions reduction scenario, that amount was equivalent to a total drawdown of ~367 PgCO2. 5 As we discussed, id. at 2-9, the temperature range and associated stable coastline of that Holocene period was conducive and essential to the development of human civilization. Page 3 of 7