FOR REVIEW. [See Publications A. S. P., Vol. VIII, p. 101.] The Call, San Francisco, California. The Chronicle, San Francisco, California. The Examiner, San Francisco, California. The Overland Monthly, San Francisco, California. The Record-Union, Sacramento, California. The Times, Los Angeles, California. The Tribune, Oakland, California. ON THE INFLUENCE OF CARBONIC ACID IN THE AIR UPON THE TEMPERATURE OF THE EARTH. BY PROFESSOR S. ARRHENIUS. [Abstract by EDWARD S. HOLDEN.] [NOTE. The following very brief and inadequate notice of an important paper presented to the Royal Swedish Academy of Sciences in December, 1895, and printed in the Philosophical Magazine, Volume XLI, pages 237-276, is given here chiefly for the purpose of directing attention to an entirely novel and simple explanation of the vexed questions relating to the Earth's temperature in past times and to the cause of the Glacial Epoch. It is impossible in the present place to give more than the shortest abstract.-E. S. H.] I. Introduction: Observations of LANGLEY on Atmospheric Absorption. "A great deal has been written on the influence of the absorption of the atmosphere upon the climate. TYNDALL,* in particular, has pointed out the enormous importance of this question. To him it was chiefly the diurnal and annual variations of the temperature that were lessened by this circumstance. Another side of the question, that has long attracted the attention of physicists, is this: Is the mean temperature of the ground in any way influenced by the presence of heat-absorbing gases in the atmosphere? FOURIER maintained that the atmosphere acts like the glass of a hot-house, because it lets through the light-rays of the Sun, but retains the dark-rays from the ground. This idea was elaborated by POUILLET; and LANGLEY was by some of his researches led to the view that "the temperature of the Earth under direct sunshine, even though our atmosphere were present, as now, would probably fall to 200° C., if that atmosphere did *The author's references to the original authorities are, in general, omitted here.E. S. H. not possess the quality of selective absorption." This view, which was founded on too wide a use of NEWTON's law of cooling, must be abandoned, as LANGLEY himself in a later memoir showed that the full Moon, which certainly does not possess any sensible heat-absorbing atmosphere, has a "mean effective temperature" of about 45° C. The air retains heat (light or dark) in two different ways. On the one hand, the heat suffers a selective diffusion on its passage through the air; on the other hand, some of the atmospheric gases absorb considerable quantities of heat. These two actions are very different. The selective diffusion is extraordinarily great for the ultra-violet rays, and diminishes continuously with increasing wave-length of the light, so that it is insensible for the rays that form the chief part of the radiation from a body of the mean temperature of the Earth. The selective absorption of the atmosphere is * * of a wholly different kind. It is not exerted by the chief mass of the air, but in a high degree by aqueous vapor and carbonic acid, which are present in the air in small quantities. * * * The influence of this absorption is comparatively small on the heat from the Sun, but must be of great importance in the transmission of rays from the Earth. * * * II. The Total Absorption by Atmospheres of Varying Composition. * * * * * III. Thermal Equilibrium on the Surface and in the Atmosphere IV. Calculation of the Variation of Temperature that would If the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetical progression. This rule — which naturally holds good only in the part investigated-will be useful for the following summary estimations. V. Geological Consequences. I should certainly not have undertaken these tedious calculations if an extraordinary interest had not been connected with them. In the Physical Society of Stockholm there have been occasionally very lively discussions on the probable causes of the ice age; and these discussions have, in my opinion, led to the conclusion that there exists as yet no satisfactory hypothesis that could explain how the climatic conditions for an ice age could be realized in so short a time as that which has elapsed from the days of the glacial epoch. The common view hitherto has been that the Earth has cooled in the lapse of time; and if one did not know that the reverse has been the case, one would certainly assert that this cooling must go on continuously. Conversations with my friend and colleague, Professor HÖGBOM, together with the discussions above referred to, led me to make a preliminary estimate of the probable effect of a variation of the atmospheric carbonic acid on the temperature of the Earth. As this estimation led to the belief that one might in this way probably find an explanation for temperature variations of 5° 10° C., I worked out the calculation more in detail, and lay it now before the public and the critics. From geological researches the fact is well established that in tertiary times there existed a vegetation and an animal life in the temperate and arctic zones that must have been conditioned by a much higher temperature than the present in the same regions.* The temperature in the arctic zones appears to have exceeded the present temperature by about eight or nine degrees. To this genial time the ice age succeeded, and this was one or more times interrupted by interglacial periods with a climate of about the same character as the present, sometimes even milder. When the ice age had its greatest extent, the countries that now enjoy the highest civilization were covered with ice. This was the case with Ireland, Britain (except a small part in the south), Holland, Denmark, Sweden and Norway, Russia (to Kiev, Orel, and Nijni Novgorod), Germany and Austria (to the Harz, Erz-Gebirge, Dresden, and Cracow). At the same time an icecap from the Alps covered Switzerland, parts of France, Bavaria (south of the Danube), the Tyrol, Styria, and other Austrian countries, and descended into the northern part of Italy. Simultaneously, too, North America was covered with ice on the west coast to the forty-seventh parallel, on the east coast to the fortieth, * For details cf. NEUMAYR, Erdgeschichte, Bd. 2, Leipzig, 1887; and GEIKIE, "The Great Ice-Age," 3d ed., London, 1894. NATHORST, Jordens Historia, p. 989, Stockholm, 1894. and in the central part to the thirty-seventh (confluence of the Mississippi and Ohio Rivers). In the most different parts of the world, too, we have found traces of a great ice age, as in the Caucasus, Asia Minor, Syria, the Himalayas, India, Thian Shan, Altai, Atlas, on Mount Kenia and Kilimandjaro (both very near to the equator), in South Africa, Australia, New Zealand, Kerguelen, Falkland Islands, Patagonia, and other parts of South America. The geologists in general are inclined to think that these glaciations were simultaneous on the whole Earth;* and this most natural view would probably have been generally accepted, if the theory of CROLL, which demands a genial age on the Southern hemisphere at the same time as an ice age on the Northern, and vice versa, had not influenced opinion. By measurements of the displacement of the snow-line we arrive at the result- and this is very concordant for different places that the temperature at that time must have been 4°-5° C. lower than at present. The last glaciation must have taken place in rather recent times, geologically speaking; so that the human race certainly had appeared at that period. Certain American geologists hold the opinion that since the close of the ice age only some 7000 to 10,000 years have elapsed, but this most probably is greatly underestimated. One may now ask, How much must the carbonic acid vary, according to our figures, in order that the temperature should attain the same values as in the tertiary and ice ages, respectively? A simple calculation shows that the temperature in the arctic regions would rise about 8° to 9° C., if the carbonic acid increased to 2.5 or 3 times its present value. In order to get the temperature of the ice age between the fortieth and fiftieth parallels, the carbonic acid in the air should sink to 0.62-0.55 of its present value (lowering of temperature 4° -5° C.). The demands of the geologists, that at the genial epochs the climate should be more uniform than now, accords very well with our theory. The geographical annual and diurnal ranges of temperature would be partly smoothed away, if the quantity of carbonic acid was augmented. The reverse would be the case (at least to a latitude of fifty degrees from the equator), if the carbonic acid diminished in amount. But in both these cases, I incline to think that the secondary action due to the regress or the progress of the snowcovering would play the most important rôle. The theory *NEUMAYR, Erdgeschichte, p. 648; NATHORST, l. c. p. 992. demands also that, roughly speaking, the whole Earth should have undergone about the same variations of temperature; so that, according to it, genial or glacial epochs must have occurred simultaneously on the whole Earth. Because of the greater nebulosity [cloudiness] of the Southern hemisphere, the variations must there have been a little less (about fifteen per cent.) than in the Northern hemisphere. The ocean currents, too, must there, as at the present time, have effaced the differences in temperature at different latitudes to a greater extent than in the Northern hemisphere. This effect also results from the greater nebulosity in the arctic zones than in the neighborhood of the equator. There is now an important question which should be answered, namely: Is it probable that such great variations in the quantity of carbonic acid as our theory requires have occurred in relatively short geological times? The answer to this question is given by Professor HÖGBOM. As his memoir on this question may not be accessible to most readers of these pages, I have summed up and translated his utterances which are of most importance to our subject: * "Although it is not possible to obtain exact quantitative expressions for the reactions in nature by which carbonic acid is developed or consumed, nevertheless there are some factors, of which one may get an approximately true estimate, and from which certain conclusions that throw light on the question may be drawn. In the first place, it seems to be of importance to compare the quantity of carbonic acid now present in the air with the If the former is insignifi quantities that are being transformed. cant in comparison with the latter, then the probability for variations is wholly other than in the opposite case. "On the supposition that the mean quantity of carbonic acid in the air reaches 0.03 vol. per cent., this number represents 0.045 per cent. by weight, or 0.342 millim. partial pressure, or 0.466 gramme of carbonic acid for every cm.2 of the Earth's surface. Reduced to carbon, this quantity would give a layer of about one millim. thickness over the Earth's surface. The quantity of carbon that is fixed in the living organic world can certainly not be estimated with the same degree of exactness; but it is evident that the numbers that might express this quantity ought to be of the same order of magnitude, so that the carbon * HÖGBOM, Svensk kemisk Tidskrift, Bd, vi, p. 169 (1894). |