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Climate Change Detective

Peering into the past to understand our future

Libby Ellwood, a research fellow at the La Brea Tar Pits, was previously an Americorps volunteer doing range management in Alaska, as part of the USDA Natural Conservation Service. She tracked reindeer herds and the plants they eat.


While Libby Ellwood was studying climate change in graduate school, she had an unusual research source: the journal entries of Henry David Thoreau. Why would a scientist studying climate change today need the transcendentalist philosopher’s notes from the 1850s? It turns out they’re the oldest records in the area with information about the timing of events in nature, like when baby birds hatch and when leaves change color in autumn — occasions that can shift due to the effects of climate change.

a photo of libby ellwood bending down to measure a small fern growing in a forest
Ellwood measuring ferns in Concord, Mass.

“To understand how climate change is impacting things, a huge part of that is understanding how things have been in the past. Henry David Thoreau wrote poetically about Walden Pond and about what plants were blooming and what birds were arriving. That was the foundation for the research I did,” says Ellwood.

The study of the timing of natural events and living things’ life cycles is called phenology. (Not to be confused at all with “phrenology,” the pseudoscientific quest to understand how people think by taking detailed measurements of their head.) Over the past 10 years, Libby’s research into phenology and the everyday effects of climate change have taken her to Massachusetts, Japan, and South Korea.

Ellwood is now a research fellow at the La Brea Tar Pits, focusing on climate change in a new way. While there aren’t any philosophical diaries buried in the asphalt seeps at this world-famous site, there is a very detailed record of the local Ice Age ecosystem hidden among the Tar Pits’ microfossils — the tiny fossilized remains of plants, rodents, snails, reptiles, and other creatures. Each little fossil helps researchers render the big picture of what the Ice Age was like here. What plants bloomed? What bugs scurried under them? What did all these Ice Age creatures eat?

Without a time machine, these small fossils are the best way to get a glimpse of what life was like at the end of the Ice Age. And when we compare that ecosystem to what we see today, we can ask big questions: How and when did things change? Why did some creatures go extinct? How did other ones manage to survive? And now that the climate is changing again (because of us), what lessons can we learn from the past to inform how best to protect wildlife today?

Before coming to the La Brea Tar Pits, the oldest records Ellwood had used in her research were Thoreau’s 150-year-old journals. Now she does work with fossils 10,000 to 50,000 years old, but it’s all part of the same big picture. “Climate change ties it all together,” says Ellwood.

libby ellwood, surrounded by fossils found in the la brea tar pits, holds a small fossil of a rabbit jaw
Inside the La Brea Tar Pits Museum Fossil Lab, Ellwood holds a microfossil of a rabbit jaw.



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