Does a proxy measure up? A framework to assess and convey proxy reliability

Abstract

Abstract. Earth scientists describe a wide range of observational measurements as “proxy measurements”. By referring to such a vast body of measurements simply as “proxy”, researchers dilute significant differences in the various ways that measurements relate to the phenomena they intend to describe. The limited language around these measurements makes it difficult for the nonspecialist to assess the reliability and uncertainty of data generated from proxy measurements. Producers and reviewers of proxy data need a common framework for conveying proxy measurement methodology, uncertainty, and applicability for a given study. We develop a functional distinction between different forms of measurement based on the different ways that their outputs (values, interpretations) relate to the phenomena they intend to describe (e.g., temperature). Paleotemperature measurements, which are used to estimate temperatures of systems in Earth's past, serve as a case study to examine and apply this new functional proxy definition. We explore the historical development and application of two widely used paleotemperature proxies, calcite δ18O and TEX86, to illustrate how different measurements relate to the phenomena they intend to describe. Both proxies are vulnerable to causal factors that interfere with their relationship with temperature but address those “confounding causal factors” in different ways. While the goal of proxy development is to fully identify, quantify, and calibrate to all confounding causal factors, the reality of proxy applications, especially for past systems, engenders unavoidable and potentially significant uncertainties. We propose a framework that allows researchers to be explicit about the limitations of their proxies and identify steps for further development. This paper underscores the ongoing effort and continued need for critical examination of proxies throughout their development and application, particularly in Earth's history, for reliable proxy interpretation.

Topics & Concepts