Paleoatmospheric Temperature Structure

Radiative equilibrium and radiative (:onvective temperature profiles fiw the Earth's evolving atmosphere have been cah.ulated. If the atmosphere evolved from one rich in carbon dioxide, and deficient in oxygen, to its present composilion, the temperature structure showed considerable change. The models of 3 to 4 billi(m years ago display steadily decreasing temperatures with altitude, being 185°K at pressures associated wilh the present-day upper stratosphere. A lapse rate feature similar to lhe presenl-day tropopause is n(,l indicated until about I billion years ago; but the slralospheric region is approximately 15°K colder lhan presently found at eompara/)le pressures. Surface temperal ures approximately l ()°K warmer than at present existed unlil nearly l billion years ago. When the oxygen content exceeded roughly 0.1 times the present level, sm'face temperatures began to de(q'ease. If bi(~logical processes are important to carbon dioxide--ozone w~riations, such "~s h~s been suggested during the Ice Ages, then estimales of surface temperature should inelu(te t he effe(q s of t)~)l h gases.