Henry David Thoreau is best known for his ethical and environmental writing. For the last ten years of his life, he devoted a portion of every day to a large-scale project to gather and analyze data on the changing phenomena of the seasons. This science is called phenology.
From April 12–September 15, 2013, Early Spring: Henry Thoreau and Climate Change was on view at the Concord Museum. This ground-breaking exhibition explored 19th-, 20th-, and 21st-century observations of seasonal natural phenomena in Concord, which has made the town one of the best places in the world to study climate change. The exhibition also provided an opportunity to examine the Museum’s Thoreau collection together with examples of Thoreau’s field notes, seasonal charts, and botanical specimens.
This online exhibition walks you through Early Spring and brings together new material for an extraordinary experience. The story of Thoreau and climate change unfolds in the context of historical objects such as Thoreau’s snowshoes and his Walden desk. Hear a soundscape of Walden Pond and listen to Guest Scholar Richard Primack on climate change in Concord. Learn how to measure snow, read Thoreau’s essay “Autumnal Tints,” track butterfly migration, and more. We invite you to Be Thoreau.
Henry Thoreau was a writer, naturalist, philosopher, and political activist best known as the author of Walden, acknowledged to be one of the great books of American literature.
Walden is based on Thoreau’s two-year (1845-1847) experiment in living simply and thinking deeply in a house he built himself on land owned by Ralph Waldo Emerson at Walden Pond in Concord. Thoreau had his green desk with him at Walden Pond and on it wrote the first draft of Walden, which was published in 1854. While at the Pond, Thoreau also wrote “Civil Disobedience,” one of the most influential essays in the worldwide democratic tradition.
The book Walden is organized as a calendar, beginning in the summer and ending in the spring. The idea of the cycles of nature, such as the seasons, captivated Thoreau, who was always interested to know his own place in nature. About the time Walden was published, Thoreau took up the systematic study of natural cycles, recording in his journal the first flowering time of hundreds of plant species, among other phenomena. He continued this study for the rest of his life.
Learn more about Henry Thoreau and Concord in An Observant Eye: The Thoreau Collection at the Concord Museum, by Concord Museum Curator David F. Wood.
Thoreau’s bedstead was photographed by the famed photographer Annie Leibovitz. See her photograph and find out more about her pilgrimage to Concord in 2012.
Read an excerpt from John Updike’s introduction to the 150th anniversary edition of Walden published by Princeton University Press.
Henry Thoreau walked in Concord for several hours every day looking carefully at the plant life around him. He took notes on the different species of grasses, wildflowers, shrubs, and trees he encountered—when their leaves emerged, when they flowered, and when their leaves turned color. This science is called phenology.
Thoreau wrote these observations (among other thoughts) into his journal each night. In this way he assembled years of observation on hundreds of species. In 1860, he began to extract these observations from his journal and to compile them into charts. The charts compiled the observations of many individual species over a number of years, allowing for comparison of flowering times and other phenomena from year to year.
In 2003, Boston University biologist Richard Primack learned about Thoreau’s data and recognized immediately that it was exactly what he was seeking for his research: an extensive, site-specific, accurate set of historical observations that he could compare with present-day observations at the same location. This comparison, building on the observations of Thoreau from the 1850s, shows that the climate does not just change from season to season; it changes in measurable ways over decades and centuries.
See a page from Thoreau’s Journal, 8 October 1852, recounting how a loon engaged Thoreau in a cat-and-mouse chase on Walden Pond. The manuscript journals (1837-61) of Henry David Thoreau are part of the collection of The Morgan Library and Museum in New York City.
Read “Uncovering, Collecting, and Analyzing Records to Investigate the Ecological Impacts of Climate Change: A Template from Thoreau’s Concord” by Richard Primack and Abraham Miller-Rushing, published in BioScience, February 2012.
Explore Ray Angelo’s “Vascular Flora of Concord, Massachusetts,” perhaps the most complete list that has been compiled to date of the vascular plant species that have been found growing wild in Concord.
Read “Drivers of leaf-out phenology and their implications for species invasions: insights from Thoreau’s Concord” by Caroline Polgar, Amanda Gallinat, and Richard Primack, published in New Phytologist, November 2013.
After years of hearing about climate change affecting distant alpine wildflowers and polar bears, Dr. Richard Primack of Boston University decided to search for evidence of climate change closer to home. When alerted to the fact that Thoreau had kept detailed records of natural phenomena in Concord, Dr. Primack and his team set out to continue Thoreau’s work and discover how a warming climate had changed the timing of seasonal life cycle events of Concord’s woods. For more information on Dr. Primack’s work, read his latest book, Walden Warming: Climate Change Comes to Thoreau’s Woods.
By comparing their own observations of natural events to those of Thoreau and other Concord naturalists who followed in Thoreau’s footsteps and recorded Concord’s environment so carefully, the Primack Lab scientists have been able to measure how seasonal events like plant flowering and leafing times, migratory bird arrival, and butterfly emergence are advancing with warming temperatures and changing over time.
There is overwhelming evidence that as the climate warms, spring is coming earlier to Concord. Concord has emerged as a living laboratory for climate change research and is regularly featured in newspapers, magazines, websites, and textbooks as one of the clearest examples in the world of the ecological effects of climate change—all building on the legacy of Thoreau.
Thoreau was interested in the ice at Walden Pond. Each winter, he measured its thickness, admired its blue color, and for 15 years took note of the day in the spring when it no longer covered most of the pond surface, an event known as ice out. Ice out, and the subsequent arrival of spring, is an important event for the organisms that live in and around the pond.
In Thoreau’s records, ice out occurred as early as March 15 and as late as April 18. The average date for ice out on Walden from 1846 to 1860 was April 1. Volunteers at Walden Pond have continued to note the date of ice out. From 1995 to 2009, ice out ranged from February 22 to April 12. The average ice out date over that period was March 17, two weeks earlier than it was when Thoreau visited. In the mild winter of 2012, ice out occurred at the end of January, something that would have amazed Thoreau.
There are perhaps no signals of spring’s arrival more welcome than the blooming of flowers and leafing of trees. Thoreau spent countless hours recording when these events happened for individual species. The timing of when plants flower and leaf out in the spring is closely tied to temperature. In years when the average temperature in March, April, and May is warmer, flowers bloom and leaves come out earlier than in colder years. Over time, as the average temperature in Concord has increased, spring has been arriving earlier.
Plants in Concord are responding to warming temperatures by flowering two days earlier for each increase in temperature of 1°F. When Thoreau was recording flowering dates, the average spring temperature was 42°F and the average date of first flowering of 32 selected species was May 15. In recent years (2004-2012), the average spring temperature has been six degrees warmer at 48°F and the average date of first flowering of those same 32 species is eleven days earlier on May 4. A similar trend is seen with leaves now emerging earlier in the spring than in Thoreau’s time.
Many people are enthusiastic about the return of familiar birds in the spring from their southern wintering grounds. Concord has the longest records of bird arrival dates in North America. This record begins with observations made by Thoreau, and has been continued until the present by a number of Concord residents over the past century and a half. These records have been analyzed to determine whether climate change is affecting bird migration timing the way it is with plant flowering times and insect emergence.
As a group, bird species tend to be less responsive to the effects of climate change than local plants and insects. Some bird species are responding to climate change by arriving in Concord earlier in warmer years than colder ones, but others have not changed their arrival dates, and a few species are even arriving later. Other species that used to migrate now spend all year in Concord, a change made possible in part by people putting out bird feeders. Because migratory birds as a group are responding to climate change at a different rate than plants and insects, there is the possibility that birds returning to Massachusetts may miss the peak abundance of their insect food source.
A warming climate in Massachusetts is leading to a shift in the distribution of butterflies. More northern butterfly species for which Massachusetts lies at the southern edge of their range are declining, while more southern species that historically live in warm temperate or subtropical habitats, such as the giant swallowtail (Papilio cresphontes) and zabulon skipper (Poanes zabulon), are expanding northward and increasingly seen in Massachusetts. Elfins and hairstreaks, two common groups of butterflies in Massachusetts, emerge as adults earlier in years with warmer springs and are responding to climate warming at a rate similar to that of plants and bees.
Caterpillars and other herbivorous insects rely on young, newly emerged leaves as an important food source, and in turn serve as food for birds, including migratory birds returning from southern wintering grounds.
“Nature herself holds her annual fair in October, not only in the streets, but in every hollow and on every hill-side.” As Thoreau eloquently describes, fall in New England is marked by the transformation of green leaves to vibrant displays of reds, oranges, and yellows. This color change marks the preparation of trees for the winter ahead and occurs in response to a mixture of factors including cooling temperature, shortening days, and declining water availability. Chlorophyll, the pigment responsible for photosynthesis and the green color of leaves, begins to break down, and trees reabsorb valuable nutrients from the leaves before the leaves eventually fall from the branches.
Although fall phenology has not been documented or studied nearly as well as seasonal events in spring, there is evidence that this shift into winter is occurring later now than in the past as a response to climate warming. Because leaf color and drop are less sensitive to temperature than budburst and flowering, the delay of autumn seems to be less pronounced than the early arrival of spring.
Snow and ice are considered integral parts of winter in New England and provide an abundance of cold-weather activities such as skiing, ice skating, ice fishing, snowshoeing, and snowball fights. With climate change, winter temperatures in New England will also become warmer. These increased temperatures have already led to more winter days with rain instead of snow and fewer days when the ground in New England is covered by snow.
Decreases in snow accumulation on the ground and ice on ponds and lakes limit our ability to enjoy winter sports in New England. Less snow also has ecological consequences. Snow insulates the soil, acting like a blanket, and in a warmer winter, a lack of snow can actually lead to deeper frost in the soil. How these deeper frosts affect the structure and ecology of the soil is being actively investigated by scientists. One effect seems to be that the populations of small insects and spiders are reduced. Small roots are also liable to be damaged when soil freezes deeply in winters with little or no snow, affecting the ability of trees to take up water and nutrients in the spring.
Henry Thoreau interests readers for many reasons – for his nature writing, his scientific observations of the natural world, his economy of self-reliance, his Transcendental philosophy, the stylistics of his prose, and his fascinating biography. His life and writing, therefore, allow readers to engage with many different areas of study. In other words, Thoreau is a great tool for an inter- and multi-disciplinary understanding of the world.
Concord’s Thoreau Trail
Concord’s Thoreau Trail, created by the Concord Museum, is a guide that provides a helpful gateway for exploring the various Thoreau-related sites and resources in Concord. Some of the sites include the Concord Museum, Sleepy Hollow Cemetery, The Thoreau Society, The Thoreau Institute at Walden Woods, Thoreau Farm, Brister’s Hill, the Concord Free Public Library, and Walden Pond. Concord’s Thoreau Trail is a walking and observational tour that encourages you to learn more about the natural environment that Thoreau studied, as well as the rich history associated with the places where he lived and worked. Download a printable version of Concord’s Thoreau Trail (PDF).
“Nature Journaling: A Page from Thoreau’s Book” Family Activity
Thoreau’s passion for writing was rivaled only by his passion for walking! This family activity will instruct kids to create their own nature journal and fill it with observations from a nature walk, just like Thoreau did in the 1800’s. Kids can complete the nature walk and journal activity individually or with family or friends. Appropriate for ages 5-12.
Henry Thoreau and Phenology
This elementary-school lesson asks: how does history apply to today’s science, and what is a citizen scientist? After an introduction to Thoreau, students will observe the natural world and report their findings on Project Budburst, a botany and phenology database website. Appropriate for grades K-5.
“A Word for Nature”: Creative Writing on the Natural World
Thoreau was careful not only in his observations of nature, but in the way he expressed his reflections on the natural world. This reading and creative writing lesson will help students of a wide age range develop their writing skills through personal reflection and the genre of nature writing. Appropriate for grades 6-12.
Science in Thoreau’s Time
This lesson, particularly relevant to high school biology, environmental, or other science classes, gives students a concise introduction to the history of science in the United States during Thoreau’s time, and his role as a “citizen scientist.” In addition to providing historical context for scientific concepts, this lesson illustrates how scientific knowledge builds upon itself over the course of decades and even centuries. Appropriate for grades 9-12.
Background photo credit: Cherrie Corey
Be Thoreau! For years, people in Concord have been collecting data and observing the natural world just like Henry Thoreau. You can do this too by becoming a Citizen Scientist. Citizen Science happens when amateur or nonprofessional scientists get involved in collecting scientific data.
Whether you observe when the birds come back in the spring, when the first green shoots appear in your garden, or measure the snowfall each winter, it’s easy to become a citizen scientist. Simply head out to a park in your local area or your own backyard and start observing. You can photograph, collect samples, or keep a journal of the plants and animals that you see.
Residents and visitors of Concord—and everywhere—can contribute to the growing body of research by learning more about citizen science organizations such as Project Budburst, Go Botany, and Audubon. Explore the resources below to learn more and get started:
Thoreau’s Writing: Print Editions
Thoreau’s Writing: Digital Libraries
Thoreau’s Writing: Manuscripts
- Houghton Library, Harvard University
- Digital Collections at Middlebury College
- The Morgan Library & Museum
- The New York Public Library
- John Hay Library, Brown University
- William Munroe Special Collections, Concord Free Public Library
Further Reading on Thoreau and Science
- An Observant Eye: The Thoreau Collection at the Concord Museum
- The Thoreau Collection at the Concord Museum
- The Citizen Science Academy
- USA National Phenology Network
- Association for the Study of Literature and Environment
- Jeffrey S. Cramer’s editions of Thoreau’s work
- Botanical Index to the Journal of Henry David Thoreau by Ray Angelo
- Autumn Migration of North American Landbirds by Elizabeth R. Ellwood, Amanda Gallinat, Richard B. Primack, and Trevor L. Lloyd-Evans
- Autumn, the neglected season in climate change research by Amanda S. Gallinat, Richard B. Primack, and David L. Wagner
- The Environmental Imagination: Thoreau, Nature Writing, and the Formation of American Culture by Lawrence Buell
- Henry David Thoreau: A Life by Laura Dassow Walls
- Seeing New Worlds: Henry David Thoreau and Nineteenth-century Natural Science by Laura Dassow Walls
- The Shores of America: Thoreau’s Inward Exploration by Sherman Paul
- Henry Thoreau: A Life of the Mind by Robert D. Richardson Jr.
- American Transcendentalism: A History by Philip Gura
- Walden’s Shore: Henry David Thoreau and Nineteenth Century Science by Robert M. Thorson
This online exhibition is made possible by a grant from the U.S. Institute of Museum and Library Services.
Early Spring: Henry Thoreau and Climate Change was an exhibition in the Wallace Kane Gallery at the Concord Museum from April 12, 2013 to September 15, 2013
Early Spring Resource Team
William Brumback, Conservation Director,
New England Wild Flower Society
Gary Clayton, Vice President for Conservation Programs,
Massachusetts Audubon Society
Libby Ellwood, Ecologist
Jayne Gordon, Director of Education and Public Programs,
Massachusetts Historical Society
Linda Harrar, Independent Executive Director and Producer
Caroline Polgar, Primack Lab, Boston University
Laura Dassow Walls, Professor of English, University of Notre Dame
Leslie Perrin Wilson, Curator, William Munroe Special
Collections at the Concord Free Public Library
Andy Wood, Coastal Plain Conservation Group
Early Spring: Henry Thoreau and Climate Change was made possible by a grant from the U.S. Institute of Museum and Library Services
Forrest and Marcie Berkley
Many thanks to Guest Scholar Richard Primack, Boston University
Institutional Lenders to the Exhibition
Harvard University Herbaria
Louisa May Alcott Memorial Association
The Morgan Library & Museum, New York
New England Botanical Club
William Munroe Special Collections at the Concord Free Public Library
Individual Lenders to the Exhibition
D’Anne Bodman and Harvey Nosowitz, Cherrie Corey, Rosita Corey,
Libby Ellwood, Sally Searles Ferbert, Sam Jaffe, Abe Miller-Rushing,
Caroline Polgar, Richard Primack
Cherrie Corey, Tim Laman, Larry Warfield, Alice Wellington, David Bohl, Robert Cheney, Vernon Doucette, Libby Ellwood, Go Botany, Sam Jaffe, Abe Miller-Rushing, Nora Murphy, Caroline Polgar, Richard Primack, Project BudBurst
Six One Seven Studios
Background photo credit: Alice Wellington
Early Spring: Henry Thoreau and Climate Change was on view in the Wallace Kane Gallery at the Concord Museum from April 12 to September 15, 2013. Photos by Cherrie Corey.