Melissa Charenko is an Assistant Professor in the Department of History and Sociology of Science at the University of Pennsylvania’s School of Arts & Sciences. Her research investigates the historical roots and development of paleo-disciplines—fields that reconstruct past environments through proxies such as pollen—and their evolving role in shaping our understanding of anthropogenic environmental change. By exploring how scientific reconstructions of past climates inform notions of deep time and environmental futures, her work bridges history, science, and environmental studies, with broad implications for addressing today’s climate crisis.

Can you share a bit about your research and how you became interested in the history of climate science?

My research looks at the history of climate from the deep past all the way into the present and future. I do this by looking at scientists who study proxies—indirect measurements from the Earth, things like tree rings, pollen, and ice cores—that tell us something about climate but don’t do so directly. Climate leaves a trace on these objects.

I became interested in and knowledgeable about proxies during my PhD program. I was interested in the interactions between the social and the scientific, and my advisor suggested I study paleoecology, or the ecology of the deep past. I started attending lab meetings of paleoecologists, some of whom were studying pollen. I had the chance to go out and core Lake Mendota in Wisconsin, being pulled behind a snowmobile to a coring site. Using a piston corer, we could go through the ice to get down to the sediments at the bottom of the lake that contain ancient pollen grains.

That inspired my dissertation research, which focused on the history of paleoecology. I realized how much people were thinking about climate through these different proxies and indirect measurements and thought, there’s a bigger question there about how we know the past and why we should trust it.

Tell us about your forthcoming book, Climate by Proxy: A History of Scientific Reconstructions of the Past and Future. What is it about, and what do you hope readers take away?

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My book is about climate proxies and the history, through the 20th century into the present, of scientists trying to understand climate and the climates of the past. Some of the ways they do that are different from what we typically consider when we think of how scientists study climate. We usually think of instruments, and we have good histories of instruments and why we should trust them, or of climate models. But there are limitations with both. Instruments only go back about 150 years, and models need data for them to produce real-world knowledge. That data comes from proxies.

The book shows us that much of what we know about climate comes from these indirect measurements: tree rings, pollen, ice cores. But those proxies have also been seen as not as good as instruments or models. My work tries to understand when and why we should trust proxies, when they’ve been used appropriately, when they haven’t been, and how to distinguish between legitimate concerns about them and scientific attacks on climate.

I also think there’s something interesting about climate in general: People use it to think about things we might not expect. The scientists I study make claims about human futures, race, and migration patterns, all while studying climate. I’m interested in how their work with proxies shapes the way they think about these larger social and political questions.

What is one surprising or favorite finding you’ve uncovered in your work on climate history and proxies?

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One reason people were skeptical about climate proxies compared to instruments or models is that proxies are indirect. You can’t go back and double-check how past temperature left its mark on a pollen assemblage. Scientists have to make inferences and best guesses. A part of the problem with that is that different types of pollen travel differently; some blow very far, while others stay local. If you’re reconstructing the climate of a place, you want to know the pollen is actually local and not blown in from far away.

One Swedish ecologist who was worried about this problem decided to use a modified vacuum cleaner that he designed to sample air as he traveled from Sweden to New York on a steamship. He wanted to see where he was encountering pollen and how far it could go. He found that pine pollen traveled several hundred kilometers. Based on his results, scientists had to develop correction factors for their climate reconstructions that made inferences from pollen. I thought that was a really interesting and creative way to solve a big problem.

In simple terms, how do climate “proxies” help us understand past climates and make better decisions for the future?

Without climate proxies to give us knowledge of the past, we would only have about 150 years of data. Climate would appear to look much the same as it does today, and we would have little understanding of climate change. We wouldn’t know that our climate is even changing. It’s only when you add the longer record from proxies that you see the steep rise—the “hockey stick*”—over the past thousand years.

Proxies are essential not just for proving that climate change is happening but also for understanding how different cultures have reacted to climate change in the past. That can inspire us to adapt or be resilient in similar ways today.

How do you involve students in your work—through research, projects, or collaborations—and what courses do you teach at Penn?

I’ve had students work on research projects related to the history of meteorology and climatology, reading old documents to figure out how scientists thought about the past and how they knew what they did.

At Penn, I teach a few courses. One is Climate and Change, a first-year seminar where students explore the question: What is climate? We all have an intuitive sense that it’s long-term weather, but there are many different ways of defining and measuring it. Our personal experiences matter, scientific understandings matter, and indigenous knowledge matters. Climate can be seen as the accumulation of different effects, but also as something that shapes—and is shaped by—human societies. In the course, we examine how people from antiquity to the present have understood climate and how they have used that knowledge, whether in colonial expansion, or in negotiating issues of race and gender—areas you might not immediately associate with the climate story.

In Spring’26, I’ll also be teaching Environment and Society, a course about the interactions between scientists, the public, and this big category we call the environment. We’ll explore where and how those interactions happen and what they mean.

Looking ahead, what changes would you like to see in sustainability, and what advice do you have for students who want to build careers in this field?

I’d like sustainability to become more interdisciplinary. I’ve gained a lot from talking with scientists, and I think they’ve gained from me too. For example, I presented at the Ecological Society of America’s annual meeting as a historian in that space, and there was a lot of mutual exchange that deepened understanding of both science as well as the humanities and social sciences.

My advice for students is to think about sustainability, environment, and climate through lots of different lenses. The solutions we currently have for climate change aren’t working; we need more voices and more kinds of voices. Plurality and interdisciplinarity are essential. Don’t think only about the hard sciences when you think about sustainability; the humanities and social sciences can contribute a lot to those dialogues too.

*The hockey stick graph is a visual representation of historical average temperatures in the Northern Hemisphere, characterized by a long period of stability followed by a sharp increase in temperatures around 1900. Its shape resembles a hockey stick, with the vertical spike symbolizing the recent rise in temperatures attributed to industrial activity and potentially anthropogenic causes. First published in 1998 by researchers Michael E. Mann, Raymond S. Bradley, and Malcolm K. Hughes, the graph became a focal point in discussions about climate change, particularly regarding the debate over whether current temperatures are historically abnormal.

Further Reading:

Weathered: Cultures of Climate by Mike Hulme. 

Climate in Motion by Deborah R. Coen