Walden Warming

Climate Change Comes to Thoreau's Woods

Richard B. Primack

• Publisher: The University of Chicago Press
• Year: 2014
• ISBN:
  9780226062211
• Topic: Biowissenschaften
• Subtopic: Ökosysteme & Lebensräume

"An unnervingly close-to-home perspective [on] the dynamics and impact of climate change on plants, birds, and myriad other species, including us."— Booklist In his meticulous notes on the natural history of Concord, Massachusetts, Henry David Thoreau records the first open flowers of highbush blueberry on May 11, 1853. If he were to look for the first blueberry flowers in Concord today, mid-May would be too late. Warming temperatures have pushed blueberry flowering three weeks earlier, and in 2012, following a period of record-breaking warmth, blueberries began flowering on April 1—six weeks earlier than in Thoreau's time. In Walden Warming, Richard B. Primack uses Thoreau and Walden, icons of the conservation movement, to track the effects of a warming climate on Concord's plants and animals, with the notes that Thoreau made years ago transformed from charming observations into scientific data sets. Primack finds that many wildflower species that Thoreau observed, including familiar groups such as irises, asters, and lilies, have declined in abundance or disappeared from Concord. Primack also describes how warming temperatures have altered other aspects of Thoreau's Concord, from the dates when ice departs from Walden Pond in late winter, to the arrival of birds in the spring, to the populations of fish, salamanders, and butterflies that live in the woodlands, river meadows, and ponds. Demonstrating the effects of climate change in a unique, concrete way using this historical and literary landmark as a touchstone, Richard Primack urges us to heed the advice Thoreau offers in Walden: to live simply and wisely. In the process, we can minimize our own contributions to our warming climate.

1. Borneo to Boston

IN 2001, I WAS CONDUCTING FIELDWORK IN Bako National Park, a rugged rain forest landscape of jagged rocks and cliffs on the northwest seacoast of Malaysian Borneo. I was studying how hundreds of different trees could coexist in a single stand in the rain forest and the ways that selective logging was affecting both the mix of species and the structure of the forest. Trees were my focus, but a spectacular variety of animals and herbaceous plants confronted me at every turn. Each morning as I set out from the field station, I could hear large proboscis monkeys calling and moving through the forest canopy above me; rattan vines cascaded down from the trees; and fallen flowers and leaves of great variety littered the forest floor. However, even though Bako National Park was a paradise for a nature-lover like myself, it was impossible for me to ignore the reality that all around the park, as well as up and down the whole island, the forest was vanishing. It was being cleared to harvest timber and to make way for palm-oil plantations.

The clearing of rain forests in Borneo and across the Old and New World tropics is having devastating consequences for biodiversity, but the destruction of tropical forests around the globe is hastening a different kind of change: climate change. Rain forests fix carbon—they are among the largest carbon reservoirs on the planet—and when people clear and burn them, tons of carbon dioxide are released into the atmosphere. People can understand how habitat destruction leads to the loss of orangutans, hummingbirds, and orchids. But what they don’t understand as well is how clearing trees in Borneo and the Amazon can affect climate on the other side of the world. Increasingly, as I measured trees and patrolled study plots, it was climate change that was on my mind.

I had made a turn earlier, with many other field biologists, to conservation biology. This relatively new branch of ecology developed in the 1980s as field biologists recognized that they could not just passively observe the destruction of the species and ecosystems they were studying. Many of us decided that we should take an active role in protecting what we observed, valued, and loved. Our role models were people like Jane Goodall, who changed from carrying out long-term studies of chimpanzees in Africa to leading global efforts on behalf of primate conservation; Dan Janzen, who has devoted his life to creating and managing the vast Guanacaste National Park in Costa Rica; and Dian Fossey, killed at her field station while aggressively defending gorillas against poaching. These three pioneers were among the champions who inspired thousands of young people and established scientists to enter the new field of conservation biology and become involved in protecting the diversity of life on Earth.

Since earning my doctorate from Duke University in 1976, I’d been following the traditional career trajectory for a field botanist. I’d been studying forest ecology in Malaysia since 1980, and I even thought of it as a second home, since that is where my wife, Margaret, and her family are from. Starting in 1990, I had increasingly begun to focus my tropical research on conservation biology. By 2001, I found myself making a second turn, to the study of climate change. Being a botanist, I would focus my attention on looking for the effects of climate change on plants, while keeping my eyes open for the impact of climate change on birds and other animals. I loved working and living in Borneo, because of its astonishing natural history and wonderful people, but I concluded that as a scientist I needed to influence opinion on environmental issues in the United States. To build a compelling case for the effects of climate change, I would need evidence of the impacts of warming temperatures not in the far-off rain forests of Malaysia, but back in the United States. People might not know or care much about proboscis monkeys and pitcher plants on the other side of the world, but they would not be able to ignore the evidence from places closer to home and species they know and care about.

After all, the whole point of global warming is that it’s a global phenomenon that affects every place on planet Earth. Indeed, showing that the effects could be felt in our own backyard, literally, was part of the point I wanted to make. It’s easy for people to be nonchalant about or ignore a distant problem, but harder to remain unconcerned when it’s up close and personal.

So, after twenty-one years of studying tropical rain forests, I decided not to return to Malaysia for another field season. I would no longer make the long flight across the Pacific, walking through the national parks of Borneo, looking up at the giant trees with awe. Instead, I would become a detective, looking for signs of climate change in the field books of long-dead naturalists and among the observations of a new generation of ecologists. All of my field notes, data sheets, maps, and computer files from Borneo were put into a file cabinet in my lab, where they will remain until either I decide to resume my tropical work or some colleague or graduate student decides to take over the project.

Late in the winter of 2001–2, I returned to Boston and began my search for signs of climate change. I didn’t know what I would find. Along with the chilly weather, I was encountering some cold receptions from my colleagues. Some of them wondered if it was really such a good idea for me to be changing my research direction at this point in my career. They pointed out that I was fifty-two years old and known as a tropical biologist; wouldn’t it be better for me just to keep working in my narrow specialty? Other colleagues were skeptical that I would actually find anything of value in old field records and regarded my quest as doomed from the start. And most alarmingly, when I began to talk about my new interests, a number of researchers told me that the National Science Foundation and other government agencies would never fund this kind of wild-goose chase and that I had better find other projects if wanted to secure grant support. After a year of searching, I still had not made any research progress or figured out how to fund this new line of work.

Just when I was starting to have major doubts about my decision to change directions, into my office in early 2003 came Abe Miller-Rushing, a prospective graduate student looking for an innovative project for his doctoral dissertation. I was able to convey my excitement to Abe, and he soon agreed to work with me to search for evidence of climate change. I didn’t tell Abe at the time, but it raised my level of confidence that at least one other person thought this idea might actually work.

We Find Thoreau’s Records

The plan I’d outlined back in Borneo, and now conveyed to Abe and my Boston colleagues, was to look closely at ecosystems in Massachusetts to see if I could observe the evidence of climate change here, right under our noses. Now that I was back in the United States, I began by limiting my focus to eastern Massachusetts, where I owned a house and had worked since 1978 as a professor at Boston University.

As the accumulated snow of 2003 began to melt and the days started to lengthen, I felt that the clock was ticking. I needed to plan my research before the flowers bloomed and the trees leafed out. The best idea that I could come up with was to record the flowering times of plants in Concord and at the Arnold Arboretum in Boston. This would generate some useful information and keep my undergraduate research assistants busy for the summer. At the same time, I would begin looking for evidence that plants, birds, insects, and other animals were changing in response to a warming climate. Plants and animals become active in the spring and dormant in the autumn; my aim was to discover whether these dates were changing and whether the change was apparent over the span of decades. If so, how could I find out? To shed light on this question, we needed data. Abe and I began searching for any old records we could compare to modern inventories.

In the spring and summer of 2003, we began to have some luck. We located journals documenting when migratory birds arrived in the spring over the past forty years. But finding records further back than 1970 proved difficult, and we still had not found any old records of plant flowering times. The whole research enterprise depended upon having a data set from fifty or more years ago to which we could compare modern numbers. But did the older data sets even exist? By the end of our first field season, we had lots of information on modern flowering times. However, despite months of scouring every library and archive we could think of, as well as polling colleagues and writing notices for newsletters and websites, we still hadn’t found the old data sets that we needed. Then, our luck changed.

Our “eureka moment” came a year into our study, when in the fall of 2003 Phil Cafaro, a friend of mine who is a professor of environmental philosophy, asked me if I knew about the flowering-time observations that Henry David Thoreau had made in Concord during the mid-1800s. As I listened with amazement, I realized that this was exactly the information we had been seeking. Phil told me that Thoreau had made observations in Concord of plant flowering times, as background to a book he was planning but never wrote on the change of seasons. It turns out that this list of flowering dates is well known to Thoreau scholars, and I was able to get a copy within days from Brad Dean, an independent Thoreau scholar living in New Hampshire. The list was everything I could have wished for: the first flowering dates of plants in Concord for the years 1851 through 1858. Thoreau, in addition to being one of the key figures of transcendentalism and a pioneer of the American conservation movement, had also made annual quantitative observations of an entire plant community. We now had our baseline data to see how plants had changed their flowering dates over time.

“A Self-Appointed Inspector”

During the fall, as I talked with Brad and then later with Jeff Cramer of the Thoreau Institute and other Thoreau scholars, I learned that Thoreau had kept extensive journals in which he recorded the seasonal phenomena he observed during his walks along the forested shores of Walden and surrounding areas of Concord. He noted the dates of flowering and leaf-out times, when birds arrived in the spring, the date of ice-out at Walden Pond, and other natural phenomena in Concord. This came as a complete surprise; I’d expected we might find records in the archives of a nineteenth-century natural history society, but not among the writings of one of the most revered and original writers in the American literary canon.

I’d read Walden in college, and I knew that Thoreau was considered one of the founding fathers of the modern conservation movement—but I had never known (nor had any other biologist that I talked to) that he’d made detailed observations of local flora and fauna while he lived out by Walden Pond between July 1845 and September 1847 and for eleven years thereafter. But these weren’t just any written observations.

Thoreau had prepared tables precisely documenting the annual flowering times of over three hundred plant species. Species occupied row after row on successive pages of surveyor’s paper, with years listed in the column heads at the top of each sheet. Thoreau had created these tables by extracting data from all of his journals. We had found our dream data set, and other data sets were to follow.

Thoreau’s natural history tables had never been published, with their existence known to only the small circle of Thoreau scholars. Once we found out about them, my colleagues and I realized that these records offered us a perfect window into the local ecology of eastern Massachusetts a century and a half ago.

In the days after we learned of the Thoreau data, I met with Abe Miller-Rushing to plan our next steps. We were excited and cautiously hopeful. There were unknowns, as there always are when setting out on a new research project. Could we find a way to use Thoreau’s observations to show whether the effects of global warming could be seen in Concord and eastern Massachusetts? At a more basic level, we had no idea whether such a project had ever been attempted and only a vague idea of how to go about it. It seemed impossible that no ecologist or botanist had ever seen or worked with these records before. And even if we could document changes in such phenomena as the appearance of spring flowers, and even if we could attribute them to climate change, what should we do about it?

The most obvious path was to build up our own data bank of observations of the same phenomena, so that we could compare the two sets of data and look for similarities and differences. We knew that the landscape of Concord had changed greatly in the 160 years between Thoreau’s observations and ours, but we also recognized that Concord, more than most suburban areas, was extremely well-protected by government agencies and private land trusts. We would have the opportunity to study the same species that Thoreau had observed in some of the same woodlands, pond edges, and river meadows, following in his footsteps.

For many years I was self-appointed inspector of snow storms and rain storms, and did my duty faithfully; surveyor, if not of highways, then of forest paths and all across-lot routes, keeping them open, and ravines bridged and passable at all seasons, where the public heel had testified to their utility. (Walden, 17)

And so in 2003, my students and I became the self-appointed inspectors of climate change in eastern Massachusetts, rediscovering old, forgotten, or underappreciated data sets, interviewing bird-watchers, and recording flowering dates of different plants. For these observations, we hiked the landscape of Concord two to three days each week every spring, noting the earliest dates that particular flowers opened up (budburst), just as Thoreau had done, as a gauge of the impacts of climate change.

At the same time that we were beginning our own observations, I was delving into Thoreau’s writings, to see what else he had to say about weather phenomena in the mid-nineteenth century. In the 1840s, the Industrial Revolution was just beginning to take hold in America. The boom in the use of coal, and its associated production of carbon dioxide, wouldn’t come until the 1870s. Thus when Thoreau began his experiment at Walden, he was more often than not writing about episodes of extreme cold, frosts, and thick ice, rather than our present focus on warming trends. His age had different preoccupations, and people were more concerned with freezing to death than suffering from extreme heat.

On Thin Ice

In the 1840s, when Thoreau was living at Walden Pond, the idea of global warming did not yet exist, nor was there any reason for anyone to propose it. The farmers and townsfolk of nearby Concord, Massachusetts, were far more concerned with cold conditions. An early spring was a phenomenon people would have greeted with pleasure, as it meant relief from heavy snows and bone-chilling temperatures.

The mid-nineteenth century was a particularly cold period, deeply felt by a largely rural society. Frosts during the summer could kill the crops upon which farmers depended for food and income. A late frost on the night of June 12, 1846, killed the beans, tomatoes, squash, corn, and potatoes that Thoreau had planted in his field. Severe winter cold could also kill livestock in unheated barns as well as wild game, such as deer, that supplied supplemental meat. During an unusually cold winter, families might run out of firewood trying to heat their houses and would experience great hardship or freeze to death. In his journal, Thoreau wrote about the extraordinary cold weather of 1810, when he was three years old:

Mother remembers the Cold Friday very well.… The people in the kitchen…drew up close to the fire, but the dishes which the Hardy girl was washing froze as fast as she washed them, close to the fire. (Journal, January 11, 1857)

Had Thoreau been able to look into the future, I imagine he would have been dismayed by some of the changes that have occurred in Concord. In particular, the effects of climate change and rising temperature are now affecting his beloved Walden Pond. In New England, one place where global warming can be seen clearly is its lakes and ponds, now covered in winter with no more than a thin veneer of ice where before there was a thick ice covering.

The failure of thick ice to form on bodies of water is a phenomenon that has happened more frequently in recent decades. In the 1950s and early 1960s, when I was growing up in Newton, Massachusetts—a suburb of Boston not far from Concord—ice-skating was a popular pastime, with hundreds and even thousands of people gathering to ice-skate on Crystal Lake and Hammond Pond. I remember crowds of people gliding across the endless glassy-smooth lake surfaces, and then gathering around log fires to warm their frozen hands. A section of the lake was set aside for pickup games of hockey. In those years, winter temperatures were typically in the teens or single digits for weeks at a time, and the ice was very thick.

During the late 1980s and early 1990s, when I wanted to bring my own children ice-skating in such a natural setting, it was hard to f...