for the CO2 molecules to be carried from the sea surface into its interior (see Figure 5.2). The longer the time available, the deeper the penetration. Between the end of World War 11 and the Arab oil boycott in 1974, the fossil fuel CO2 production hacl accelerated at a pace averaging close to 3% per year. Were this pace continued, the mean age of fossil fuel molecules would approach 69 In 2/3, or 33 years. However, as in the decades preceding W orld War II and during the past tw o decades, the rate of increase has been less steep, so the mean age is closer to 40 years.

Taken together, the distributions of natural and bomb-test radiocarbon suggest that the fraction of the ocean's capacity utilized increases roughly as the square root of the penetration time (see Figure 5.3)* So if, for example, the rate of rise in emissions were to be reduced to 1% per year, then at the end of the 21st century, the mean age of CO? molecules would approach 71) years (i.e., In 2 yr.). The fraction of the ocean ventilated would rise by a factor approaching v/70/40, or 1.3. In the extreme, if fossil fuel use were to cease in the year 2000, the mean age of the excess CO2 molecules in the year 2100 would be 140 years and the fraction of the sea's capacity to be utilized would increase by 140/40, or by about a factor approaching 2. Hence, if these rules apply, no matter what scenario is envisioned for the nest century, no more than 30% of the ocean's capacity for partitioning will be utilized by the year 2100.

Hut how reliable is the square root relationship? Although the distribution of natural radiocarbon constrains the rate at w hich CO^ is carried into the deep sea by way

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Guide to Alternative Fuels

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