Blowing in the Wind: Pollen's Mobility as a Challenge to Measuring Climate by Proxy, 1916-1939

This article examines how geologists, botanists, and ecologists used pollen as a proxy for past climates in the first half of the twentieth century. It focuses on a particular challenge of measuring climate with pollen: pollen's mobility. As scientists came to learn, pollen from some vegetation is more mobile than others. Pollen's differential mobility challenged regional climatic conclusions because of the potential mixing of pollen from various locations. To minimize the effects of this problem, pollen analysts sought to decrease the noise produced by highly local or foreign pollen. Yet, many ground-truthing and calibration methods were not available to pollen analysts because of the temporal separation between the observer and the object of interest. Instead, pollen analysts had to make spatial meaning out of fossil pollen using empirical studies of modern pollen, inferences from macrofossils and successional history, and applying statistical theories to fossil pollen data. Many of these corrections factors relied on pollen analysts' knowledge of place, including elements like the location's topography, prevailing winds, and plant cover. These elements were a natural part of vegetation-pollen-climate interactions. Scientists needed to account for them to turn pollen into a proxy for climate. Pollen's movement was equally natural, but scientists decided to eliminate some pollen to augment the regional climate signal. These selective eliminations of place suggest that not all elements of place are equally important. Scientists had to omit some elements of place to make sense of the complexities of the natural world.