Special Release: Climate change, tree rings, and string theory

Marvel being interviewed at the 2019 Voices for Science workshop. Credit: AGU

What’s it like to be one of the most well-known climate scientists around? People (e.g. your dad) should just trust what you say, right? Well…it doesn’t always work out like that.

Kate Marvel, Associate Research Scientist at NASA Goddard Institute for Space Studies and Columbia Engineering’s Department of Applied Physics and Mathematics, started as a theoretical physicist before shifting to studying climate change. In addition to her research, she writes a regular column, “Hot Planet,” for Scientific American. She’s also an AGU Voices for Science Advocate. 

This episode was produced and mixed by Shane M Hanlon.


Shane Hanlon (00:01):

Hi everyone.

Lauren (00:01):

Hey Shane.

Nanci Bompey (00:02):

Hi Shane. Hi Lauren.

Shane Hanlon (00:04):

Oh, we have three of us today. How’s everyone doing? We’re all still at home.

Lauren (00:10):

We’re in quarantine. It’s actually not so bad now.

Shane Hanlon (00:13):

I mean, just to be clear, none of us are actually in quarantine, right?

Lauren (00:16):

We’re just staying at home.

Shane Hanlon (00:17):

Yeah, we’re all isolating still.

Nanci Bompey (00:19):

So how’s it been? Lauren you said you’re really actually getting used to it or enjoying it a little bit?

Lauren (00:24):

I think I’m into a groove now. I’m kind of enjoying it. You know, the sleeping in, the just kind of wearing loose, comfortable clothing all day.

Shane Hanlon (00:32):

I got to say, I mean I obviously wish the circumstances were very different, but my partner and I just moved and honestly the process during all of this and moving and finding a house and all that, it was actually kind of aided by being home all the time. Because we could just like get up on, like we’d get a call from our realtor like, “Hey, can you look at a house today at noon?” And if I was in work that would’ve been able to happen. And so again, wish the scenario was different, but it’s actually been nice being at home. And I like working at home.

Lauren (01:00):

I do too. Although I just realized the other day, I can’t remember what shoes I used to wear.

Nanci Bompey (01:07):

That is a very good point.

Lauren (01:09):

Like I only wear flip flops now or slippers.

Shane Hanlon (01:14):

Oh my God, that’s amazing.

Nanci Bompey (01:15):

That’s funny. But things were, I guess, very different a year ago when you guys recorded this episode?

Shane Hanlon (01:20):

Yeah. Yeah. We were in the building and we’ll get into that.

            Welcome to the American Geophysical Union’s podcast about the scientists and the methods behind the science. These are the stories you won’t read in the manuscript or hear in a lecture. I’m Shane Hanlon.

Nanci Bompey (01:20):

And I’m Nanci Bompey.

Shane Hanlon (01:40):

And this is Third Pod from the Sun.

            So yeah, like Nanci said, we recorded this interview a year ago, a little over a year ago. So this is our third Voices For Science episode, where we talked about one of our advocates who’s a climate scientist at NASA and Columbia. She has a regular column in Scientific American and quite the impressive Twitter following.

Kate Marvel (02:05):

My name is Kate Marvel. I am a research scientist at Columbia University and the NASA Goddard Institute for Space Studies. I am a climate scientist and I am interested in understanding what climate change looks like right now and what it’s going to look like in the future.

Shane Hanlon (02:22):

Climate science is pretty, I think, nebulous to a lot of folks. What does your research involve?

Kate Marvel (02:30):

Right. So a lot of times when we think about climate change, we think about global warming. We think about the average temperature of the planet increasing. But most of us don’t care about that because nobody actually experiences the average temperature of the entire planet. We care how that affects the scales that we live at and things that we care about like rainfall patterns and cloud cover. So I’m really interested in what climate change means for the scales and the variables that affect us.

Lauren (03:01):

So what are kind of those variables? What are the effects that we could feel like on a local level?

Kate Marvel (03:07):

So there is evidence that humans are already changing global rainfall patterns. We are making, broadly speaking, wet areas wetter and dry areas dryer. And because we are changing the circulation of the planet, the motion of air and water in the atmosphere, we’re actually changing the locations of those wet and dry regions. So that’s something that is really, really difficult to think about and to sit with. There’s some evidence that human activities are changing cloud cover patterns. So in some areas it’s getting cloudier, in some areas it’s getting clearer. And the kind of clouds that we’re experiencing are changing.

            There is evidence based on tree rings and meteorological data sets that humans actually affected global drought risk as early as the beginning of the 20th century.

Shane Hanlon (03:07):


Lauren (03:55):


Kate Marvel (03:55):


Lauren (03:56):

So tell us a little bit more about that, if you can.

Kate Marvel (03:58):

So that was a really fun study to work on because the guy whose office is next door to me at NASA is an expert on drought and tree rings. And I was bored one day so I just walked into his office and I said, “Hey Ben, tell me about these tree rings.” And so he started telling me how they would drill into trees and then get this record of tree rings. And my first question was, “Do you hurt the trees?” And he was like, “No, it’s painless. It’s like tree acupuncture.”

Lauren (04:26):

Valid question.

Kate Marvel (04:26):

It’s a valid question, right? But the width of the tree rings on any given year tells you something about how moist the soil was, which tells you something about the conditions when that tree was growing. And there are thousands of tree rings that have been sampled, thousands of these records all over the globe. And we can take these thousands of trees and correlate them together into things called drought atlases. So what we did is we put together a global picture of all the drought atlases that have been collected so far. And then what that allowed us to do was to really evaluate how unusual things that we’re seeing right now and we saw in the 20th century where, against that backdrop of things that the climate did before the industrial revolution. Because these give us records that go back to 1400 and even earlier.

Lauren (05:19):

So actually, let me stop you for one second. So with a tree ring, what’s the furthest you can go back? Is it just like the life of the tree? And what’s like the oldest tree that’s ever been cored?

Kate Marvel (05:30):

So I’m not the tree ring expert. That’s the guy in the office next door to me. But there are these drought atlases. Some of them go back to the beginning of the millennium. So zero Common Era. And that’s using supplements from petrified wood. You have pretty good coverage that goes back to about 1400. So we can tell what droughts were doing in the middle ages, which, as a non tree ring specialist, really blows my mind. I think that’s really crazy. But that kind of gets us something that I’ve always been really worried about.

            Because we don’t really know what the world looks like without us. We don’t really have any recent observations of the climate without a lot of greenhouse gases in the atmosphere. And so in order to see if something we observe is strange, we generally have to use climate models to estimate that pre-industrial variability. That what the climate would do naturally. And I think these models are really credible. A lot of really smart, dedicated people have worked really hard on them. But you always open yourself up to criticism that you’re just using a model to estimate climate variability. And this allows us to get around that because we’re not using a model to estimate that internal climate variability, we’re using actual tree ring measurements. And so what our study did is we took a global perspective, and it was really important to take that global perspective because …

            I’m from California, California gets droughts all the time. Australia gets droughts all the time. The Mediterranean gets droughts all the time. But if California and Australia and the Mediterranean all simultaneously experience a drying trend, that’s kind of weird. And so it’s that spatial coverage, that real global perspective, that can really help you separate out the signal from the noise. So what we found is the tree rings kind of increasingly looked like what we would expect greenhouse gases to do to drought conditions. They showed conditions increasingly resembling that, what we call a human fingerprint. And this happened until about the middle of the 20th century. And in the middle of the 20th century, things start to turn around. Things start to look a little bit different. And we don’t have a great solid explanation for this yet, but we’re pretty sure that it has something to do with the increased concentrations of gas and dust that we call aerosols in the atmosphere during that time.

            In about the late ’70s, with the advent of clean air legislation, we see that start to clean up a little bit, and then we see the greenhouse gases start to play a bigger and bigger role. So we see these areas start to begin to dry out again simultaneously. So what we found is that humans very likely influenced 20th century drought conditions in kind of three distinct stages. So we saw humans were largely creating this drought pattern through our emission of greenhouse gases up until about the 1950s. And then from about the 1950s to the middle or end of the 1970s, our aerosol emissions actually had a much bigger effect on drought risk. And then, with cleaning up the air with the Clean Air Act, with that sort reduction in what we would call the aerosol burden, we start to see things turn around. And every single climate model, every single thing that we have to predict this, is basically telling us we should expect unprecedented drought risk worldwide by the middle of this century.

Shane Hanlon (09:15):

Climate change is consensus except for that small minority out there for whom it isn’t, I guess. And Kate has received her fair share of comments from folks who are deniers. And I think she said the largest demographic were retired engineers, but I wanted to know in particular if there were any others that stood out. It seems like a lot of your job is interacting. Not only doing the science, but interacting with people. Whether that’s in person or phone or whatever else. Do you have any really memorable experiences you’ve had with folks? It could be anything, but I’m thinking like whether you changed someone’s mind or had a surprising experience in a positive or negative way. I feel like there’s so many opportunities to just sit down and talk with people. I’m just kind of wondering if there’s anything that really sticks out to you or anyone you’ve ever talked to or interacted with?

Kate Marvel (10:14):

For me one of the most memorable transformations that I’ve watched is seeing my dad, who identifies as conservative and lives in Indiana, come around to accepting climate change as real and serious. And I would like to say that I changed his mind, and I totally did not. The thing that changed his mind actually was the insurance industry. He thought long and hard and he realized that if climate change was not real, if it was a hoax, an insurance company could come along and offer lower rates and undercut the competition and put them all out of business because they don’t have any incentive to believe climate change if it’s not real. But none of them do that. And that got him to thinking maybe if these companies were willing to put their money on the line, maybe there’s something to this.

            And I think that was important because that spoke to his values. He views himself as he believes in free markets. He believes in capitalism. And if I tell him, “Hey Dad, look at all these graphs and charts and IPCC reports,” he’s not going to listen to me because he hasn’t built trust with that. That’s not part of his self image. But this very sort of like hard-nose financial motivation for insurance companies, that was the thing that really changed his mind. And I feel like that kind of like teaches me humility. Like if you can’t change your dad’s mind but an insurance company can, what are you doing?

Shane Hanlon (11:56):

Kind of along similar lines about interacting with people, do you have any desires, like if you could like sit down with one person or get your message out to one community or whatever it is, who would that be? And, I guess, why?

Kate Marvel (12:20):

I really want to meet David Attenborough.

Lauren (12:23):

Of course.

Kate Marvel (12:23):

Just because who doesn’t want to meet David Attenborough? I would love for him to speak up more. And I think he’s beginning to do it because he’s such a trusted face and voice. I’m really excited by the freshmen class in Congress. I think there are a lot of people who are really starting to change the narrative in saying you don’t care about climate change or the economy, you don’t care about climate change or jobs, you don’t care about climate change or equity, you have to care about all these things because everything is intertwined. And I think whatever your political stance, I think that is a message that is really supported by the science. That you can’t separate out a rise in global average temperatures from the planet that that is happening too. So I am really heartened by that.

            I do think it is really important that climate change be a political issue. And correct me if I’m wrong, I think in the 2016 presidential debates there were no questions asked about climate change. I think that’s unacceptable. I hope that that’s not going to happen in 2020. We already see in the Democratic primary, a lot of the candidates actually talking about this. And my entire goal as a science communicator is to kind of be irrelevant. I just want to talk about cool science. I don’t really want to be part of this political debate. And I’m really hoping that eventually we’ll get to that point when you don’t really need a scientist to say, “Oh yeah, it’s real.” Because you’re arguing about solutions and you’re arguing about the best timescales and what to do right now and what to do later and investment in the future. So I really hope that eventually we can change our political system and move to that point.

            I would say because I transitioned into climate science after my PhD which is in physics, I asked a lot of really stupid question to a lot of really brilliant people, and they were so generous with their time, and I think that is something that’s so essential to science, is creating environments where people feel comfortable asking dumb questions, and that’s something that I’m really invested in creating for the scientific community moving forward, because it was so, so important to me. 22:07

Shane Hanlon (14:23):

I find it interesting that she transitioned out of physics into climate science. I actually don’t know like what a normal, or the most common transition is.

Nanci Bompey (14:37):

That is interesting. I heard Lauren was quite interested in this physics part.

Lauren (14:42):

I was. I’m really interested in particle physics and string theory. It’s so fascinating to me.

Nanci Bompey (14:47):

That is so interesting. I don’t think I knew that about you.

Lauren (14:50):

Yeah. It’s kind of a weird like science thing where I geek out. I mean, I just want to know, it’s like, “hat is everything? What is all this stuff? What is it? What does it mean?”

Shane Hanlon (14:59):

Yeah. And she got a little stuck, but it was okay.

Lauren (15:03):

So what made you decide to switch your master physics to climate science?

Kate Marvel (15:09):

I did my PhD in a very esoteric branch of physics called string theory.

Lauren (15:13):

I love string theory. I mean that I’m not just like, yeah, I do. I’ve read so many books about it. To me it’s so fascinating.

Kate Marvel (15:22):

Yeah. Not a lot of experimental evidence for it.

Lauren (15:25):

No, but the whole thing, it just fascinates me though. Yeah.

Kate Marvel (15:28):

Yeah. That’s why I went into it, because I was like, “What? Quantum gravity, that’s amazing.” And then I just kind of got frustrated with the lack of experimental evidence and the lack of what I saw as relevance to everyday life. And I wanted to do something more applied. Having a physics background is really helpful and I’m really glad I found this.

Lauren (15:52):


Shane Hanlon (15:53):

And you get to talk to Lauren about string theory.

Lauren (15:54):

Yeah. Oh my God. I would love to pick your brain about string theory. I have so many questions.

Shane Hanlon (15:59):

Luckily for me, we ran out of time. So we didn’t quite get a chance to dive really deep into string theory.

Lauren (16:08):

Yeah. I’m kind of upset that we got cut off, but I hope I can pick Kate’s brain another time.

Nanci Bompey (16:14):

You can watch that movie. Have you seen that Particle Fever?

Lauren (16:18):

Oh, of course. Great, great film.

Shane Hanlon (16:21):

Ooh yeah. I like Particle Fever.

            We actually talk about how it’s a good … there are some terrible science documentaries out there, it’s a good one.

Nanci Bompey (16:26):

That’s great. And you don’t even have to care about the science. It’s just like the excitement.

Lauren (16:31):

It’s great. It’s about the people and about the discovery and it’s such a great film.

Shane Hanlon (16:36):

So we’ll do a future mini episode where we just digest that and talk about it and we’ll do like a movie review.

Lauren (16:41):

Oh, I’m so super excited for that. I have so many thoughts.

Shane Hanlon (16:45):

Oh, I’m sure. All right. Well that’s all from Third Pod from the Sun.

Nanci Bompey (16:52):

Thanks so much to Lauren and Shane for bringing us this episode. And for Kate for sharing her work with us.

Shane Hanlon (16:58):

And this podcast was produced and mixed by me.

Nanci Bompey (17:01):

And don’t forget to rate and review us on Apple Podcasts. And you can always check us out wherever you get your podcasts or at thirdpodfromthesun.com.

Shane Hanlon (17:10):

Thanks all, and we’ll see you next time.

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