HISTORICAL CHANGES IN CONCENTRATIONS OF ATMOSPHERIC TRACE CONSTITUENTS, 1700 - 1985.

Preserved samples of ancient atmospheres and evaluated historical measurements provide surprisingly informative picture of the concentrations and trends of a number of the atmosphere's trace constituents over the past few centuries. The information is sometimes local in scope, sometimes global. In either situation, examples of which are discussed herein, the general picture is the same: gradual increases the atmospheric constituent concentrations from the dates of the earliest reliable measurements, followed by dramatic increases in concentration in the twentieth century. With this historical perspective and with detailed models, much of these results can be reproduced and the forecasts made for atmospheres of the future. Although in a few instances there have been recent decreasing concentration trends on local and regional scales, the global outlook is for continued increases in the concentrations and impacts of many atmospheric trace species, with possibility of major, but still relatively unpredictable, effects on climate and the stability of the atmospheric photochemical system.