The Natural Breakdown of the Present Interglacial and its Possible Intervention by Human Activities

Abstract

On the premise that climate responds in a stable and well-behaved manner to changes of terrestrial or extraterrestrial conditions of environment, the question of anticipating when the present interglacial will break down is explored from two different viewpoints. The concept, that the timing of the breakdown can be inferred through a comparison of the duration of the present interglacial (to date) with the duration of previous interglacials of similar warmth in the upper Quaternary, is examined from the viewpoint of the chronology of changes of solar radiation received at the top of the atmosphere, generally recognized as a likely causative agent in the development of interglacials. It is found that the radiation changes around the time of the present interglacial are somewhat different in character from those that accompanied the last interglacial, but that the radiation changes around the time of the last interglacial were more nearly similar to those which may have accompanied earlier interglacials. From this viewpoint, comparisons drawn between the present and previous interglacials are judged to be of uncertain value as a predictive tool for the future. The principal effects of man's activities on present-day climate are then reviewed. and the thermal effects of anticipated future increases of atmospheric carbon dioxide and particle loading are compared. It is concluded that the net impact of human activities on the climate of future decades and centuries is quite likely to be one of warming, and therefore favorable to the perpetuation of the present interglacial.