When Melissa Charenko was working on her Ph.D. in the history of science at the University of Wisconsin-Madison, she started attending meetings of a paleoecology lab. On one excursion, she rode behind a snowmobile across a frozen Wisconsin lake as climate scientists drilled through the ice to collect sediment cores containing fossil pollen grains.

Charenko, now an assistant professor in Penn’s Department of History & Sociology of Science, says, “I was literally along for the ride as a historian.” She notes that the cores collected that day allowed scientists to infer climate conditions for a few thousand years of history. The experience got her thinking about how “past climates become explanations for the present,” she says.

Sediment cores containing pollen are one example of an indirect measure of past climates—known as proxies—whereas direct measures include thermometers and rain gauges. But instrumental records only go back about 150 years, Charenko says, meaning other methods like proxies are needed to get climate insights for most of Earth’s history. Read more within Penn Today.