-t - t!ue, it ean be calculated that a lIttle over 502 of the CO2 enterlng the ataosphere 1s reoalning thele and the rest ls belng absorbed ln aurface slnks on the contineDts or ln the oceao. ExtrapoletLag backnerds ln tlne to fo1low the history of fossl1 fuel corobuetlon, lt can be estlDated that slnce 1850 the coacentratloo of this gas ln the atEosphere has lncreased by about 132. Thls iacrease sDounts to about 75 bl111on netrlc tona of carbon dloxlde. It ls also posslble to extlapolate lnto the future. One of the Dost cormonly guoted exttapolatlons is that-of the oak Rldge Natlonal Laboratory whlch was publlshed in 1976r. Thls study produced two scenarlos for the grorrth of fossil fuel coasrnptlorr (Vugraph 3). Prior Eo 1973, fossl1 fuel use had beea growf.ng exponentlally at about 4.37. pet yeat. The scenarlo for nost rapld growth as€rned that this gronth rate nould coutlaue, Eodlfled by a depletlon factor whlch reduced the exponent ln proportlon to the aoount of foesll fuel whlch temalned unburned. Thel! second end uore cooselvative assuaption presuaed ihat fosel1 fuel utllLzatlon would grow wlth a 2Z grolrth late out to 2025 A.D. follolred by a srtetrlcal decrease. Ttrls latter Ecenario is cloae to that developed indepeadently by the CoordlDatlon and Plaanlng DepartEent of the E:o(on Corporatlon. Vugraph 4 plesents the predicted atuospherlc carbon dioxlde 1eve1s whlch would result from each of these scenarlos. The vertical axls in thls vuglaph preseuts the atuospherLc carbon dloxlde concentlatlon lelat1ve to that shlch was calculated to have exlsted ln 1850, prlor to the corobu8tlon of appreclable anounts of fossll fuel. It can be seen that the acenarlo baeed upon very rapid gronth pledictE thst by 2075 the atDosphellc carbon dloxlde concentretlon w111 be about 4 to 5 tlDes that whLch exlEted prlor to the lndustrlal revolution. Moreover, at that tLne, the carbon dloxlde concentratloa ry'111 sti11 be Lncreasing. The Dore conservatlve assunptlon, showtr ilr the lol'e! curve, predicts that carbon dloxlde concentratlons \ri1l level out about a century frm now at a value shlch 1s about tlrice that ln exlstence ln 1850 and then nould declLne at a very s1o!r !ste. Although carbon dloxlde Lnclease is predomlnantly attrlbuted to foss11 fuel conbustlon, lo8t sclentlEts agree that more research ls needed !o deflnltely establlsh thls relatlonshlp. The posslbillty rhat Ehe lncleasfng carbon dloxlde ln the atnosphere Ls due to a change lfl the natural balance ha6 aot yet beeD ellelnated. In fact, a look at the Eagnltude of the aatural lnterchanges, as shovn 1n Vugtaph 5, shows that thls posslbillty should be taken Berlously. The data 1n Vugraph 5 are taken floD a Scientlflc Workshop on Atmospherlc C02 spouaored by the World Meteorologlcal Organizatlon Ln Deceober 1976. The vugraph sho\rs the fluxeg of CO2 lnto and out of the atnosphe"e 1n un1t6 of blll1ons of netlic tons of -arbon per year. It