Assessing past climate changes from proxy records: an iterative process between discovery and observations

Abstract

The past state of the atmosphere is obtained from the analyses of diverse 'proxy samples'. Progress has been made in the last few decades due to: (1) discovery of new proxy matrices; (2) discovery of new methods of characterizing and reading the proxies, and (3) synthesis of information obtained from diverse proxy records from different parts of the globe. The science of reading multiple records in a proxy matrix is a synergistic activity, which leads to both validation, and growth of knowledge. This field is now emerging as an artful field where the scientist has gained uncanny skills in reading the evolutionary history of the earth's atmosphere over a wide range of time scales from decades to millions of years. There is no scarcity of proxy records. As matter evolves, it continually leaves behind proxies of great variety. Our capability to use them depends primarily on technological abilities to determine the nature and veracity of the recording matrix. Examples are presented of important climatic information that is currently available about the environment of the atmosphere, using the techniques available to date. These include recently developed methods of determination of atmospheric carbon dioxide concentrations to several hundred millions of years in the past, and cosmogenic methods for studying climate, atmospheric aridity and solar activity in the past several thousand to millions of years.