Kate Marvel: Physicist, Climate Scientist Part II

The California drought: does the climate change 'signal' stand out above the 

weather 'noise'? [Figure credit: Jeff Master's Wunderblog]

In the second half of this interview with Dr. Kate Marvel of the NASA Goddard Institute for Space Studies, we discuss her field of climate science. We cover uncertainty, the hunt for signal in noisy data, and the joy of seeing physics work. In her case that joy is a mixed blessing because her data are backing up models that can, at times, make somewhat depressing predictions. All views expressed here are her own.

LK: You’ve been in the thick of comparing different climate models, and seeing how well these models agree with each other, seeing how they’re doing in various tests. What would you want to say about the state of the art here, and the description of our uncertainty? 

KM: There is an incredible amount of uncertainty, and for me that is the scariest thing. It’s not true, but I think you could make an argument that wasn't that wrong if you were to say “We don’t know that much more than we did back in the 1800s.” We know that there’s a greenhouse effect; we know that carbon dioxide is a greenhouse gas. And just from looking at that we know that if you put a bunch of carbon dioxide in the atmosphere, the Earth is probably going to warm.

And then you see it empirically, in the historical record?

I do a lot of what’s called detection and attribution -- basically trying to figure out what climate change looks like. You might say this is easy: “Duh, it’s global warming.” But what does climate change look like in terms of changes to rainfall patterns or cloud cover, for example? And so we try to understand from basic physics what would happen, what is supposed to happen under climate change. And then looking at observational records; looking at the satellites or ground-based gauges or whatever and saying, “Okay, this thing that we expect to be happening; is it happening?” It’s this weird cognitive dissonance, because you get really excited when you can show when it’s happening, because it’s very elegant. You’re like, “This is what physics tells me to expect; this is what the models are saying; ooh look it’s happening!” Then you kind of realize, “Oh my god, it’s happening!” And that’s a little depressing.

The earth is super complicated, and there are a lot of things that could happen to either speed up or slow down the warming. For example, you melt the ice caps, and that’s a positive feedback – it speeds up the warming. Because you used to have things that were reflecting incident short-wave radiation and now it’s absorbing and re-radiating long wave. So that’s a positive feedback. Warmer air holds more water vapor, and water vapor’s a greenhouse gas, so you make the earth warmer, you get more water vapor, and that accelerates the warming.

But then there are possible negative feedbacks. So if you increase cloud cover down low, then that can kind of reflect more incoming solar radiation and slow down the warming. And it turns out we just don’t understand clouds. We’re making progress, but if you think about how to model cloud formation, that is something that’s really affected by very small scales. Like you put bits of dust up in the atmosphere and you can seed clouds. And that’s really hard to incorporate in a global climate model, because global climate models happen on really big scales, and these processes happen on really small scales. You can’t explicitly resolve them; you have to parameterize them. And it turns out that as a result, we just don’t understand the net effect of cloud changes in the future. And you know, I think we’re making some progress on narrowing that down, but it’s kind of the biggest source of uncertainty right now.

Well people must also be thinking then of seeding clouds; intentionally creating clouds.

Yeah. I mean, there’s a lot of work being done on what’s called Solar Radiation Management, which is either like “Let’s try to increase cloud cover,” or just like “Let’s put a bunch of junk up in the stratosphere so that we decrease the amount of solar radiation coming to the lower atmosphere and hitting the Earth.” People have done a lot of modeling studies, but I think there’s kind of a general consensus that nobody wants to do this. There are so many uncertainties and it would be so much better if we didn’t have to do this. But it doesn’t benefit anybody to be completely clueless about it.

I did a carbon audit on myself a few months ago; just on one of these sites where you can enter some simple information. And not surprisingly, my footprint is dominated by flying. And it’s something I’ve wrestled with: what do I do about that? And I’m wondering, so certainly you’re doing science; you benefit greatly from being able to talk to other people and there’s benefits to actually being there in person. How do you think about your own carbon footprint, your own contribution to this problem given the work you’re doing, what you’re focused on?

I try to draw a very firm line between what I do scientifically and what I do personally. Because I do know that there is a science of communication, like “What is the best way to talk to people about these things?” And telling people to stop having fun is not ever going to work. And so I would be thrilled if we had a conversation about what’s the best way to mitigate climate change. And I don’t know, I feel like there are a lot of really smart people thinking about this, people who have training in economics and sociology, etc. It’s not that I feel that it’s not my place, because I have my personal beliefs, but I don’t think we’re there yet. We’re still arguing about whether climate change is a thing and I would just be so thrilled if we stopped having that argument.

We’re still arguing about whether climate change is a thing? What do you mean by that?

I feel like a lot of the political discourse is talking about “Is this happening?” And I find that so frustrating because what should be arguing about it is “What should we do?” And to even be having the discussion would make me so happy. So I’m kind of trying to work on trying to shift the conversation from “Is climate change happening?” And my answer is yes. And “Are we responsible?” And the answer is almost definitely yes. And then trying to move that to “What should we do?”

“I’m kind of trying to work on trying to shift the conversation from “Is climate change happening?” And my answer is yes. And “Are we responsible?” And the answer is almost definitely yes. And then trying to move that to “What should we do?”

So how do you go about that? That sounds to me a) fundamentally important and b) really difficult, and fundamentally ripe with the possibility of tremendous frustration.

I think it is. I mean, there are some really smart people thinking about the best ways to communicate this. And I think that so far there is a consensus: the consensus is “You can’t just tell people more facts.” Like there’s this thing called the Deficit Model, which says “Well, people don’t believe science because they don’t understand it. So if you just tell them more facts, they’ll accept it.” And I think the consensus is that this approach is just not going to work. And part of it is, you have to restrain yourself. So when somebody says something like “There is no climate change,” or “Vaccines don’t work,” or “Evolution is clearly not happening,” then your first impulse as a scientist is to be like, “Well you’re wrong. You’re wrong and I’m going to tell you why you’re wrong.” And I think that’s just a human impulse – we don’t like it when other people are wrong. But you have to kind of suppress that impulse. It’s kind of like eating Krispy Kreme doughnuts: it’s going to make you feel really good in the short term, but you’re really going to regret it in the long term and it’s probably not worth that short term pleasure.

And a lot of it is tribal. A lot of it is, “I want to be the kind of person who believes in and does something about climate change, because it’s bound up with all of these other things that I accept politically.” Or “I don’t want to be the kind of person that does something about climate change because then I’ll have to accept all these things that I just don’t.” And I think it’s trying to come up with ways to say to people who don’t accept a lot of things which they associate with left-wing political ideologies, and to say, “No, there is room for you here. It is possible to create a narrative that includes you.” And I think that is more productive.

There’s a woman called Katharine Hayhoe who’s at Texas Tech. She’s an amazing climate scientist, but she’s also an evangelical Christian. So she is very good at bridging that gap and telling people that it’s okay; there’s room for people like us here. And I think a lot of what she does can then be undermined by a shouty atheist coming along and saying “No, accepting science immediately means that you have to give up all of your beliefs.” There’s nothing wrong with being an atheist; I don’t think there’s anything wrong with being a believer. And I think that there is room for everybody here, but that means that those of us who are scientists kind of have to suppress that urge to tell people that they’re being stupid when we think they’re being stupid.

I choose not to eat meat, because honestly I don't care for it, and I don't drive because I live in a dense city with decent subway service.  But I don't think my personal choices should necessarily be universal, and I don't think it helps to tell other people to give up things that make them happy.

“. . . When somebody says something like “There is no climate change,” or “Vaccines don’t work,” or “Evolution is clearly not happening,” then your first impulse as a scientist is to be like, “Well you’re wrong. You’re wrong and I’m going to tell you why you’re wrong.” And I think that’s just a human impulse – we don’t like it when other people are wrong. But you have to kind of suppress that impulse.”

There’s a book by Naomi Klein in which she argues that conservatives are scared of this for the right reasons, because meeting this challenge means we have to rethink fundamental things about the free market system. Do you care to comment?

I have no idea if that narrative is correct because I’m not an economist. I know that some people are saying, “Okay, we have to completely overhaul capitalism,” and some people are saying, “No, we just need to price externalities right and there’s a free market way to do that.” And I know which position I’m sympathetic to because of my own personal politics, but I think me talking about that would be like me talking about criminal justice or reproductive rights in the sense that I have my beliefs about this, but I don’t claim expertise on that, you know what I mean?

Yes, and I respect your reticence very much. 

Is there anything from the science you’re working on now that you want to tell me about? Questions that you’re digging into that are really fascinating you? You said you’re working on basically figuring out what the predictions are for things like rain patterns and then going and trying to verify those in the historical record, or see what you learned from what we know. Anything that was surprising in this process or really cool?

I just think it’s great. I think one of the great things about climate is that there are so many Big Questions to answer. So you can do these things like, “Okay, how much wind power can we extract from the atmosphere?” Or “What is happening to rainfall patterns?” You can ask these very big questions and I really like that. I’ve gotten really obsessed with clouds, which is ironic because I hate bad weather and I’m only happy when it’s sunny outside, but know your enemy, right? So I’ve been doing a lot of work on clouds. Because I think this is a really interesting question, and we’ve been able to show that you can actually see things happening in the observations in clouds. At least in a couple data sets, you can see clouds rising, which is what’s predicted under global warming conditions.

What do you mean, you can see them rising?

So we’ve got cloud satellites dating back to the early 80’s, and in the satellite data, you can basically see the fingerprint of human-caused climate change in the cloud records, which is really surprising, because they’re so noisy, and so difficult to get anything out of. But you can really start to see all of these patterns emerging and it’s amazing how coherent everything is.

So you mean the typical height of the clouds above the land is changing?

Yeah. So I mean the height of high clouds is changing. So these big thunderheads that you would see, like convective clouds in the tropics, those are rising, those are going higher in ways that are predicted very robustly by a lot of the climate models and some of the physics underlying them, which is incredible. If you look at what climate change is supposed to do to rainfall, there are two basic underlying physical concepts. One, warmer air holds more water vapor, so all else being equal, wet areas will get wetter and dry areas will get drier. Two, all else is not equal, and we expect changes to atmospheric dynamics, which means the locations of those wet and dry areas are moving. And if you look at the satellite records you can see that the wet areas are getting wetter and the dry areas are getting drier and the entire pattern is moving poleward in basically exactly the way that you think it should. So that’s kind of amazing to see theory go to models, go to observations, in quite such a straightforward way.

I can see why you would get excited.

Yeah, maybe like, “Oh man!” <laughs>

So wet areas getting wetter, dry areas getting drier, and then everything moving around, that final statement – there’s no meaning in it then, unless the predictions are quite specific on how things are moving around. And they are?

Yeah.

So we’re in what looks like the fourth year now of a drought in California. What does this work actually say about particulars like that? Is this likely associated with climate change? Is it just consistent with what we expect? How do I think about this drought in the context of climate change?

The smaller the scales you’re looking at, the more complicated the picture becomes. So if you’re just looking at the California drought: I think the story that’s emerging is that it’s consistent with things that have happened before naturally, so the California drought looks like natural variability. But that doesn’t mean that it’s not influenced by climate change. So I think the tricky thing to try to understand, and the tricky thing to communicate, is that there’s no such thing as weather independent of climate. It’s like personality and mood; weather is mood and climate is personality. But obviously your moods are affected by your personality. And so the California drought – things like that have happened before, things like that would probably happen even if we weren’t doing anything to change the climate, but the California drought is happening in the context of climate change. And so just because it’s consistent with natural variability, that doesn’t rule out a role for climate change. It’s just that the role of climate change is really difficult to disentangle, if that makes sense. There are some things that are more clear-cut; the extreme heat events they're experiencing in Australia are very unlikely to happen without systemic climate change. And so there are things that are more clear-cut than others, and the California drought is kind of in that non-clear-cut category.

“. . . It’s like personality and mood; weather is mood and climate is personality. But obviously your moods are affected by your personality. And so the California drought – things like that have happened before, things like that would probably happen even if we weren’t doing anything to change the climate, but the California drought is happening in the context of climate change.”

Well, it’s like that in cosmology, where there are certain signals we can only dig out of the noise by stacking, so I guess that’s the case here with climate in California: you look at the patterns globally and I guess that’s what you’re saying about dry areas getting drier, wet areas getting wetter. In particular areas you can’t separate out that signal from the weather variability noise. But more globally you’re seeing the signals emerge.

Yeah, exactly. I mean, that’s even how we use that language. We talk about things as a signal to noise problem. Just because there’s a lot of noise and you can’t pick out the signal, it doesn’t mean that the signal doesn't exist. But the signal of climate change is getting louder and louder, and we're starting to pick it up in more places.