Segment from Revisionist Climate

I Speak for the Trees

Thomas Jefferson & Benjamin Franklin have different ideas about how to warm up the chilly American climate, and trees may be on the chopping block. Historian Joyce Chaplin explains.


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BRIAN: Major funding for BackStory is provided by an anonymous donor, The National Endowment for the Humanities, the University of Virginia, The Joseph and Robert Cornell Memorial Foundation, and The Arthur Vining Davis Foundations.

ED: From the Virginia Foundation for the Humanities, this is BackStory.

NATHAN: Welcome to BackStory, the show that explains the history behind today’s headlines. I’m Nathan Connolly.

BRIAN: I’m Brian Balogh

ED: And I’m Ed Ayers. I know we’re in the dog days of summer right now, but imagine that it’s the dead of winter. And because this is BackStory, let’s go back to wintertime in 18th century New England.

BRIAN: Uh-oh.

JOYCE CHAPLIN: It was unexpectedly and frighteningly cold even to the indigenous inhabitants.

NATHAN: This is historian Joyce Chaplin.

JOYCE CHAPLIN: Winter as it approaches is just a kind of horrible thing that haunts you, that you’re not sure you can survive, and that kind of beats at you year, after year, after year.

NATHAN: Chaplin says that in early America winters were especially brutal.

JOYCE CHAPLIN: Boston Harbor freezes over in the 1740s. And for one winter it’s said that people can actually walk from some of the outlying islands to Boston over parts of the ice that are thick enough. This is just unthinkable now, of course.

NATHAN: Colonists we’re experiencing the effects of what we now call the Little Ice Age. This was a period of cooling which lasted from the year 1300 until about 1850. Winters were so long and harsh that some years were described as a year without summer.

JOYCE CHAPLIN: The cold really affects the earliest colonists who are completely unprepared and they had not expected that there would be many feet of snow that would last many, many months.

NATHAN: That’s because their understanding of climate was based on the idea of latitude.

JOYCE CHAPLIN: It was the way the ancient Greek geographers had described the different zones of the world and why those around the equator seemed hotter than those toward the poles. Most of the parts of the new world that the English would settle in, including New England, should be far enough south, if you compare them across the Atlantic Ocean, to have the same crops as Spain or Italy. And they clearly don’t have the climates to do that. They don’t now, let alone during the past. So there is already description of the new world as posing a problem for understanding how the old definitions of climate, as latitude, should actually work.

NATHAN: In other words, those old definitions had to be revised.

JOYCE CHAPLIN: By the 18th century, there are definitions of climate that begin to talk in terms of a system of complexity. And that’s the way we think of climate today. That it’s not a fixed system. It changes. It changes hourly, it changes daily, it changes over the decades.

NATHAN: Chaplin says this was the moment when our modern understanding of a climate in flux first came into focus. It was a critical breakthrough, because back then understanding the weather was a matter of life and death.

MALE SPEAKER: New findings on the effect of climate change in the US–

FEMALE SPEAKER: A report obtained by The New York Times found the average temperature in the US has gone up rapidly since 1980.

MALE SPEAKER: But scientists say it’s more than temperatures, they have connected man-made climate change to deadly heat waves, droughts, and devastating floods.

MALE SPEAKER: Another study by scientists from 13 federal agencies directly contradicts claims by the president and some cabinet officials who say that human contribution to climate change is uncertain.

BRIAN: Last year was the warmest year on record, but 2017 could be even hotter. Since the late 19th century the Earth’s average temperature has risen about two degrees. Most of that rise comes from increased carbon dioxide emissions into the atmosphere. Now two degrees might not sound like much, but scientists fear that those rising temperatures could produce even more extreme weather, famines, and millions of climate refugees.

ED: Americans have long been fascinated by climate patterns and how those patterns affect their lives. So today on this show, a history of how Americans interact with and try to control the planet. We’ll hear about an early 20th century scheme to make it rain in Southern California, a scheme that worked a little too well, and a secret pentagon plan to weaponize the weather.

BRIAN: But first, let’s return to those long icy North American winters in the 17th and 18th centuries.

NATHAN: At the dawn of the republic concerns about the climate were also concerns about national security. Chapin says lots of folks, including the founding fathers, debated about how to deal with the young nation’s harsh climate.

JOYCE CHAPLIN: Being scientifically literate was culturally important during this period of time and you weren’t really a well educated person unless you knew some science.

NATHAN: Is there an earlier version of a climate debate happening among the founders in this period?

JOYCE CHAPLIN: That’s what’s really interesting about this period? Is that not only were there now theories of climate being complex, but there are also complexities within the argument about it. So there was not one theory. There was not one opinion. There was a big interesting argument about it all.

NATHAN: So Ed, Brian, take a guess at some of the ways that people thought they could fix the climate.

BRIAN: I’m guessing prayer.

ED: Recycling?

NATHAN: Nice try both. But the most popular theory, which originated in Europe, suggested that cutting down trees would produce warmer, more comfortable temperatures.

JOYCE CHAPLIN: They were convinced that forests, too many trees, actually shaded the Earth from the sun.

ED: Wait, so they actually thought trees were bad?

NATHAN: Well, kind of.

JOYCE CHAPLIN: Land that had been overgrown with weeds and wild vegetation, if it were cleared and planted with crops, and all that land turned up with hoes or plows, that also would have a warming effect on the climate. And so we also see coming into focus a sense of anthropogenic climate change. What humans do affects the climate. The idea that humans on a large scale could transform the average temperature for entire regions, if not continents, was quite new. And yet this is what settlers in North America start talking about doing.

NATHAN: This idea was actively promoted by science nerd turned US President Thomas Jefferson.

JOYCE CHAPLIN: So Jefferson was an advocate, or a proponent, for clearing land, bringing it under cultivation through European style agriculture. And in some ways this is a criticism of the indigenous inhabitants who he thought had not brought enough of the land under cultivation, and that therefore the country was cooler than it actually needed to be.

NATHAN: So given these ideas about the link between deforestation and climate change being bandied about, did people actually deforest on a mass scale to bring about these ends?

JOYCE CHAPLIN: The deforestation took place on a mass scale whether people were really doing it to make the weather warmer or not. It just happened because a lot of settlers were moving across land and taking down forests in order to create farmland. It’s true that into the 19th century there was this other belief that land that was cleared would bring rain. So when people moved out into the Great Plains area, where there had been historic droughts, there was nevertheless a belief the rain follows the plow. That once lands are brought under cultivation the rain will come.

NATHAN: So the plow comes first then the cloud comes after? Wow, that’s something.

JOYCE CHAPLIN: Yes, exactly. And only after several terrible droughts and people failing was there a kind of concession that maybe not.

NATHAN: While Jefferson and others were actively trying to warm things up, America’s leading scientists thought cutting down all the trees was a terrible plan.

JOYCE CHAPLIN: So Benjamin Franklin warned that taking down all the trees, or too many trees, might make the summers unbearably hot. So be careful. And be careful what you wish for. That if you really, really want a warm climate, fine. But having a climate that was going to be too hot was not going to be good.

NATHAN: Franklin, who had been studying climate fluctuations for a while, started by printing daily weather reports in his newspaper, and in Poor Richard’s Almanac.

JOYCE CHAPLIN: Where, very conventionally, he reports on what the average temperatures were supposed to be, what the prevailing conditions, kind of odd weather events, storms, significant changes in weather, unexpected patterns. And these include the freezing over of Boston Harbor, really bad winter weather that begin to intrigue him because he starts tying them back into a theory that these are not just stray events, but part of a longer term shift.

NATHAN: And in trying to make sense of that shift Franklin collected data on a grander scale.

JOYCE CHAPLIN: Franklin does study heat and weather in a lot of parts of the world. So eventually he makes observations about medieval Europe, different parts of the Americas, even as far away as Russia. So he really is aware of how global climates operated in contrast to each other, and how specific weather patterns were particular to different parts of the world. So in some ways he has a bigger geography that he comments on than perhaps Jefferson was doing in relation to Virginia, and to parts of North America, and the United States specifically.

NATHAN: Benjamin Franklin’s interest in patterns of hot and cold led him to a more sophisticated understanding of the climate itself.

JOYCE CHAPLIN: And in this way he contributes to early theorization about atmospheric circulation and oceanic circulation. How it is that patterns of hot and cold move over hemispheres over continents and over oceans. He describes, for instance, the circulation of hot air out of the Gulf of Mexico, up the continent, and eventually across the Atlantic Ocean. And he connects this to the phenomenon that we now call the Gulf Stream.

So that sense of circulation and of a kind of irregular pattern of heat and cold moving north and south as well as east and west, that was one of the biggest challenges to this old idea of climate as latitude.

JOYCE CHAPLIN: Now we use an idea today of something called a Little Ice Age. They might not have used that language back then, but they certainly were aware that there were things happening kind of across many different generations that were reflecting changes in the environment. Is there a sense that the Ice Age, or the kind of long period of cold, that the founders were considering and that Jefferson and Franklin were debating, that has come to some kind of end?

JOYCE CHAPLIN: I gather from geologists that we’re not sure it’s over. We could still be in a period of global cooling, but we have forced the climate to be warmer, and that’s overriding the cooler stage that we would be in otherwise, which is kind of terrifying to think about that it would be even hotter. What we’re doing in terms of forcing carbon to the atmosphere would make things even hotter than it would be if we didn’t have this period of global cooling that’s still going on.

It does seem that the Little Ice Age, the conditions that were described from the late Middle Ages into the colonial period was fading over the course of the 19th century. We think it was still operating when Napoleon’s troops march out of Moscow in much colder weather than they had anticipated. It may still have been operating in to the 1840s, and up to perhaps about 1850, but the second half of the 19th century though, all of the components the Little Ice Age, extreme weather conditions, longer winters, freezing over of bodies of water, those stop being commented on, and we’ve entered a new age.

NATHAN: So, Joyce, can you give me any sense of what Native Americans might have thought about the Little Ice Age? Do we even know?

JOYCE CHAPLIN: Oh, I wish we knew more. And we need to know more. And this will require a lot of experts in indigenous languages and archeology to really expand our understanding. Because without that we actually don’t know a lot about how human adaptation to climates in North America would have worked before 1492, and it’s really essential that we do that.

NATHAN: And the way that the founders observed and debated the nature of climate change and human activity, are there any lessons from that we could point to and draw from today?

JOYCE CHAPLIN: I guess I’m always skeptical about the claim that anything that happens now is historically unprecedented. Because in some sense that self-congratulatory. Everything new happens to us. Whatever we are undergoing now, or talking about now, has never happened to anyone in the world ever before. Well, maybe so, but I think we want to eliminate the possibility that, actually, it’s happened before.

Yes, we may be living within something unprecedented in terms of anthropogenic climate change, that we have done it, but we’re not the first people to live in a period of rapid or dramatic climate change. And looking at everyone who has done that before could be incredibly useful for us.


ED: Joyce Chaplin is a professor of History at Harvard University and author of The First Scientific American, Benjamin Franklin and the Pursuit of Genius.