It could be
smaller than that or larger, depending on the way that temperature varies with height; but it will not be larger than twice that, provided that a
temporary saturation doesn't happen and then significantly reverse in the span of a single doubling — in other words, provided that the process of any
temporary saturation and following reversal (wherein BTc0 increases, halts, and then
decreases, or in the opposite order) can be sufficiently resolved by the fractional change in CO2.