THE GREENHOUSE EFFECT J. F. Black, Products Research Dlvisidn E:r:con Research and Engineerlag Co. SI'MMARY The earthts atmosphere presently contains about 330 pprn of CO2. gas does not absorb an appreciable amount of the incoming solar This energy but lt can absorb and return part of the lnfrared radiatlon whlch the earth radiates toward space. COZ, therefore, contrlbutes to warming the lower atmosphere by what has been ca1led the rrGreenhouse Effect.r' The C02 content of the atmosphere has been monltored slnce at two Locations, the Mauna Loa Observatory, Hawaii and the South PoIe. These and other shorter studies show that CO2 Ls increasing. If the Lncrease is attributed to the combustion of fossil fuels, it can be calcuLated that the CO2 content of the atmosphere has already been ral.sed by about 10 to L5% and that slightLy trore than half of the C02 released by fossil fueL combustion is remalning in the atmosphere. Assuni.ng that the percentage of the CO2 renaining in the atmosphere rr111 stay at 532 as fossil fuel consumptlon Lncreases, one recent study predicts that ln 2075 A.D., COZ concentratlon will peak at a Level about twLce what could be considered normal. This predictlon assrrmes that fosstl fueL consumptlon will grorr at a rate of 27" per year until 2025 A.D. after which lt wl1L follow a syuretrlcal decrease. This growth curve is close to that predicted by Exxonrs Corporate Planning L957 Departnent. Matheuatical uodels for predicting the clinatic effect of a not progressed to the poi.nt at whieh all the feedback which ean be lmportant to the outcome can be included. I,lhat interactlons is considered the best presently available climate model for treatlng the Greenhouse Effect predlcts that a doubling of the C02 concentratlon ln the atmosphere would produce a mean temperature increase of about 2"C to 3oC over most of the earth. The model also predicts that the temperature lncrease near the poJ-es may be t!f,o to three times this value. C02 lncrease have The CO2 increase rneasured to date is not capable of producing an effect large enough to be distlnguished from norual clinate variations. As an example of normal varl.ations, studies of meteorological and historlcal records in England indlcate that the mean temperature has varied over a range of about t0.7oC ln the past 1000 years. A study of past climates suggests that if the earth does become warmerrmore rainfall should result. But an increase as large as 2"C would probably also affect the dlstrlbutlon of the rainfall. A possibl-e result night be a shlft of both the desert and the fertile areas of the g1-obe toward higher l-atitudes. Some countries would benefit but others could have their agricuJ-tural output reduced or destroyed. The picture is too unclear to predict which countrles might be affected favorabJ-y or unfavorably.