Ken Caldeira | The climate impact of hydrogen leaks demystified
To put it in Bill Gates' words, Ken is phenomenal at translating deeply scientific concepts for people without scientific expertise. Ken Caldeira is Senior Scientist at Breakthrough Energy and Staff Scientist at Carnegie Institution for Science. As an atmospheric scientist, he demystifies the climate impact of hydrogen leakage. Under the motto "I like to say that the questions we ask are driven by our values, the answers we get should be independent of our values”, he brings a valuable unbiased scientific perspective to the topic.
Ken Caldeira is a Senior Scientist (emeritus) in Carnegie Science's Department of Global Ecology and also a Senior Scientist at Breakthrough Energy.
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This article is part of the series: Hydrogen Innovators Podcast
Transcript
[00:00:03.05] Ken Caldeira: The main climate effect of hydrogen leakage is lengthening the lifetime of other greenhouse gases that are already in the atmosphere. A lot of the controversy over hydrogen has really been this question about how much do we emphasize the next decade or two relative to the next century or two, because everybody recognizes that if you're worried about long term climate change, that CO2 persists in the atmosphere for many centuries, whereas methane goes away on the timescale of a decade. With electrolytic hydrogen, with carbon neutral electricity, that it's already a big win on this short time scale and it's like a huge, huge win on the longer time scales.
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[00:00:58.12] Karen Baert: Dear listeners, welcome to this week's episode of Hydrogen Innovators, a podcast series is produced by the Stanford Hydrogen Initiative spotlighting bold innovators in hydrogen all the way from academia to industry. You can find our podcast series, Hydrogen Innovators, on Spotify or Apple Podcasts.
[00:01:16.42] I'm Karen Baert, recent Stanford MBA graduate, entrepreneur, and innovation strategist at the initiative, and I'm thrilled to be your host for this week's podcast. Today, we have the privilege to welcome Ken Caldeira. Ken, welcome to the Hydrogen Innovators podcast. We are thrilled to learn from you today.
[00:01:34.39] Ken Caldeira: Great to be here.
[00:01:35.74] Karen Baert: Ken is an atmospheric scientist. He's a senior staff scientist at the Carnegie Institute for Science, Department of Global Ecology, and Professor at the Stanford University Department of Earth System Sciences. Ken leads the research group on the Stanford campus focused on energy systems and energy, climate, economic modeling. On top of that, Ken is also a senior scientist at Breakthrough Energy, and he's been helping to bring information and expertise to Bill Gates since 2007.
[00:02:05.48] Ken has a very wide spectrum approach to analyzing the world's energy and climate systems. He's been studying the global carbon cycle, marine biogeochemistry, ocean acidification, the atmosphere, ocean carbon cycle, and climate change. Ken lives in San Francisco with his wife, Lillian, and his grown child, Kirill. In addition to his family, he loves music. He has a home recording studio. He loves hiking, skiing, and most recently, tennis.
[00:02:34.46] Ken, you are truly a pioneer in climate change research. Back in 2007, you were already writing op eds about climate change, some of them published in The New York Times. You've been an important scientific voice advancing conversations around climate change for decades. Tell us a bit more about the different roles, Carnegie, Stanford, Breakthrough Energy, and what they mean to you, and what has changed in climate change research across the years.
[00:03:01.21] Ken Caldeira: Well, that was quite an introduction. Thank you very much. Yeah, so I wear a lot of different hats, but most of them are about generating and communicating information. And I, in my professional work, try to distinguish between normative and prescriptive kind of work, telling people what they should do. And I try to stick pretty closely to generating information and communicating that information and trying to be as neutral as possible in my professional work.
[00:03:31.41] That doesn't mean I don't have my own political opinions personally, but I think it's really important to try to give as unvarnished a representation of the truth as I can manage. So in my role up at Breakthrough Energy, which is my main paying job, my basic role is to bring information into the organization and also into the constellation of other organizations that are up there that are working on similar things.
[00:04:00.86] And again, there are a bunch of smart people there, so I need to tell people what to do. I can just bring them the information and they can decide what to do based on that information. And when I first started working up there, I thought, oh, I need to bring them all kinds of information on energy systems. It turns out, well, energy systems is actually one of the areas that they're pretty strong on.
[00:04:22.33] Where they're less strong on is the climate system and the geophysical parts of it, and what are limits to wind power and all this stuff. And so I've actually started going back a little bit more towards the geophysical side. So that's the Breakthrough Energy and Gates' world.
[00:04:38.12] And then here on the Stanford campus, Bill is kind enough to give money for a half dozen postdocs for me to mentor. And they're employees of Carnegie Institution and I have an emeritus status at Carnegie. And so I still mentor a group here, which is really great, because I'm in the fortunate position of not having any specific deliverables and so I just try to think about, what's the highest return on investment activity that we can do? And then try to influence the postdocs to work on that.
[00:05:10.58] And so we tend to do a lot of little kind of skirmish kind of science where we see an opportunity to do something relatively small scale, let's say a postdoc-led project, and address that gap as fast as we can. And also, I get a sense of, OK, what is Bill interested in, or what may Breakthrough Energy be interested in, and can we get ahead of the curve on that and do some work so that when they're ready to address those issues we've got a bunch of work?
[00:05:41.21] Karen Baert: Mhm. Interesting. So in some way you also bridge industry and academia because you hear what industry is looking for.
[00:05:48.44] Ken Caldeira: Yeah. And it's not just industry, it's also the policy people. Yeah, before-- so I started working up in the Gates' world around 2020, although it's been more than 15 years that I've been helping bring information up there.
[00:06:03.47] And before that I think we looked at if we could get a paper published in Nature magazine or a high quality journal, that that was the goal of our work was to get a publication. Whereas now we wanted to say, OK, what decisions are people making that we might be able to influence by providing additional information on this topic?
[00:06:29.09] Karen Baert: I love that thinking. Let's dive straight into that topic, hydrogen, and the impact on the atmosphere when it gets released to the atmosphere. To quickly set the stage here, so the whole point of replacing fossil fuels with clean hydrogen in certain applications is to reduce the flow of greenhouse gases into the atmosphere, and hence mitigate climate change.
[00:06:50.45] Now, what is the benefit of replacing fossil fuel with hydrogen? Hydrogen is a clean fuel. There's no carbon in the molecule. It's H2. And hence when you burn it, there's no carbon emissions. But it's important to recognize that hydrogen isn't completely harmless either. One climate concern has been largely absent in recent conversations and assessments, and that is, in case of hydrogen leakage, the warming effects from hydrogen.
[00:07:18.58] And the answer we get from most industry participants is it's unclear. More research needs to be done. Again, as an atmospheric scientist, you're well-positioned to answer this question. Enlighten us. What happens when hydrogen is released into the atmosphere?
[00:07:34.32] Ken Caldeira: So first of all, there is substantial scientific uncertainty. But this uncertainty, the low end of uncertainty to the high end of uncertainty is no more than a factor of two, so we kind of know the order of magnitude of the effect. But if you want to get a specific digit, there can be some quibbling about the exact number, but more or less the impact of hydrogen is well-established.
[00:08:00.78] And you're right that hydrogen itself is not a greenhouse gas, but hydrogen in the atmosphere on the timescale of maybe two or three years reacts with hydroxyl radical. And hydroxyl radical is the kind of scavenger ion in the atmosphere, and that also plays an important role in reacting with methane. So hydroxyl radicals in the atmosphere react with atmospheric methane to make carbon dioxide and water vapor. And carbon dioxide is much less potent greenhouse gas than methane, so that reduces greatly the climate impact of that methane.
[00:08:41.64] And so if you have a lot of hydrogen leakage, you're sweeping up some of this hydroxyl radical, and that's allowing the methane to last longer in the atmosphere. So the main climate effect of hydrogen leakage is lengthening the lifetime of other greenhouse gases that are already in the atmosphere. And now there's a bunch of timescales. And one of the interesting things about this whole research area is that there's always values and normative decisions wrapped up with scientific and technical information.
[00:09:18.97] So you have to decide-- so let's say you release some greenhouse gas and it warms the Earth for some amount of time. And maybe while the Earth's warming, it's causing different kinds of damage in different places. And so this question of how do you value the amount of damage that happens at different times and different places. And that's complicated, of course, because the cost of avoiding the leakage is borne by whoever's doing it, so there's also social and political context to it.
[00:09:52.73] But even though the effect of the hydrogen directly in the atmosphere only lasts a couple of years after the release, it lengthens the timescale of methane from maybe 10 years to 11 years or something like this. And so the effect on the increased methane can take a few decades to go away. And so even though the hydrogen is only in the atmosphere for a couple of years, the climate effect can last a couple of decades.
[00:10:20.04] But one thing everybody agrees is that over long timescales, let's say over centuries, hydrogen or even methane, that those go away in the atmosphere within decades. And so if you're concerned about melting the ice sheets and making parts of the tropics uninhabitable due to high temperatures and humidity, then you're really concerned about these long term constraints. And the question is how much attention should we be putting to near-term climate change.
[00:10:54.90] Karen Baert: When discussing hydrogen leakage, I'd like to draw a parallel with methane leakage. We've been working on increasing transparency around methane leakage and reducing methane leaks for decades. Now hydrogen is a tiny, tiny molecule, and hence an extremely volatile gas. It's often referred to as the escape artist. So I would assume that avoiding hydrogen leakage will be even more challenging than avoiding methane leakage, and that inevitably hydrogen leakage rates will be higher. We'd love to hear your thoughts on that.
[00:11:30.49] Ken Caldeira: So hydrogen can be quite a leaky gas. It's a hard-- it's a small molecule that doesn't like to stay contained. And even at a hydrogen filling station to fill cars, it's not uncommon to have 10% leakage. And at 10% leakage on the timescale of a few years, let's say the hydrogen was made with electrolysis from the carbon neutral electricity source.
[00:12:01.84] In a 10% leak, you could maybe in the first decade get something like one third of the climate effect that you would get from the fossil fuel CO2. But once you're a few decades out, there's basically no warming from the hydrogen leakage, whereas the CO2 from the fossil fuel burning keeps the Earth warm for many centuries. And so if your main goal is to keep Antarctica from melting, then the long time scales are really important.
[00:12:34.78] If you're mostly concerned about near-term impacts in the next decades, then the leakage becomes more important. Now with hydrogen, first of all, there's an economic incentive to avoid leakage because if you're-- it costs a lot of money to make hydrogen, and if you're leaking all this hydrogen, you're losing money. So there is incentive to bring down leakage. And one would hope that a lot of its work should be done to avoiding that leakage.
[00:13:05.76] But if it could get down to, say, a percent leakage, then the kind of effects are basically negligible that with electrolytic hydrogen, with carbon neutral electricity, that it's already a big win on this short time scale, and it's like a huge, huge win on the longer time scales. A more sort of challenging thing is one of the cheapest ways to make hydrogen today is steam methane reforming, starting with natural gas. And there you have to worry about the methane leakage in addition to the hydrogen leakage.
[00:13:41.73] And if the methane leakage is substantial, say over 3% or 4%, something like this, then you can have-- it could be on the decadal time scale worse than just burning the methane directly. But even in that case, after a few decades, you're hugely better off with the hydrogen.
[00:14:01.83] But a lot of the controversy over hydrogen has really been this question about how much do we emphasize the next decade or two relative to the next century or two, because everybody recognizes that if you're worried about long term climate change, that CO2 persists in the atmosphere for many centuries, whereas methane goes away on the timescale of a decade.
[00:14:29.65] Karen Baert: Fascinating. And it's a great overview. And also I think it explains why the answer is not that straightforward, right? There's a lot of different components. There's leakage rates and how much you can avoid that, there's radiative forcing of the molecule, but also just how that evolves over time. And you alluded to it earlier where you said you see your role as a scientist to provide people with information and leave the interpretation up to them.
[00:14:54.81] Ken Caldeira: Yeah. I mean, I obviously have my own emphasis. What I would say is that the questions we ask are driven by our values, but the answers we get should be independent of our values.
[00:15:06.03] Karen Baert: Now, let's go back to the question of what happens when a hydrogen molecule escapes to the atmosphere and how do we compare that to the impact other molecules have. As an engineer, I like to quantify things. So in my research ahead of this interview, I was trying to figure out what is the global warming potential or what are the estimates. And the most narrow range I could find was something between seven and nine.
[00:15:30.97] To clarify for our listeners, a global warming potential is the heat absorbed by any greenhouse gas in the atmosphere as a multiple of the heat that would be absorbed by the same mass of carbon dioxide. So it's kind of the relative climate impact compared to carbon dioxide. And just as a reference, natural gas, methane has a global warming potential of 23. How accurate do you believe that range is, and why is it so difficult to estimate?
[00:15:54.84] Ken Caldeira: Well that's seven to nine. I think others have got numbers up to 11. The first thing I like to say is that the metric itself, global warming potential-- this is the hundred year global warming potential-- first of all, it's a little confusing because it's based on the mass of the molecule. So CO2 is 44 grams per mole-- and mole is what scientists use to measure amounts of molecules of things-- whereas hydrogen is 2 grams per mole.
[00:16:30.43] Karen Baert: And then I guess if you compare it on the energy content basis, so by megajoules, the comparison is also different.
[00:16:37.61] Ken Caldeira: Right. And that's a similar thing, that if-- I don't have the numbers right in my head, but if you say burning methane, which is 16 grams per mole, versus hydrogen, which is 2 grams per mole, that, yeah, I think it's more or less on a molar basis, a factor of three difference or something like this. I forget the exact number. But yeah, and so these global warming potentials, I think it's-- for most purposes, I think looking on an equal energy basis kind of gives the most understanding.
[00:17:08.61] Karen Baert: Now, what we are asking ourselves in the industry and what I'm sure our listeners are asking themselves is knowing that there's a lot of uncertainty on the actual negative impacts of hydrogen when it leaks to the atmosphere. Could it be that by replacing fossil fuels with hydrogen, we actually make things worse?
[00:17:30.05] Ken Caldeira: I think that's almost impossible given our current state of knowledge. Maybe if you leaked over a third of the hydrogen you made, then you could be a little bit worse for a couple of years. But then again, a few decades down the road would be hugely better off. And so I think the bigger risk, really, is when you have methane derived hydrogen, the methane leakage.
[00:18:00.36] And so my personal view is really that I think there's a lot of economic incentives to avoid hydrogen leakage and also safety incentives to avoid hydrogen leakage. I think people will have a lot of incentive to address hydrogen leakage for those other reasons, and that climatically it's really a secondary gas.
[00:18:29.80] As an atmospheric scientist, I don't feel that there is a lot of uncertainty. And so I almost feel like this repeating, oh, there's a bunch of uncertainty in what happens with hydrogen, it's almost counterproductive because it's just the normal kind of climate science uncertainty and it's not any--
[00:18:47.84] Karen Baert: Yeah.
[00:18:48.38] Ken Caldeira: It's as understood as almost any other gas.
[00:18:51.04] Karen Baert: Well, that's exactly why we're here today, so thanks for helping us understand that. Now, moving away briefly from the atmospheric sciences, you've done a lot of work on broader energy systems modeling. Based on your experience there, we'd love to hear your thoughts on the cost of green hydrogen and its role in a decarbonized world.
[00:19:16.93] Ken Caldeira: If we do simulations of an electricity system today with current prices and we demand that it be it wind and solar based system, so we're not allowing natural gas in the system, we're not allowing nuclear, then today, hooking electrolysis up to the wind and solar, making hydrogen, storing it in geologic caverns, and using that through a fuel cell to feed electricity to meet peak demand, that that is the cheapest way today at current prices.
[00:19:53.09] And that's despite a huge-- not that high of round trip efficiency. I think it's something like-- I forget what it is. 60% or something like this. And one of the things we're finding is that it's really all about the capital cost of the electrolyzer and the fuel cell, and that the round trip efficiency is not that important in these systems because when you have so much wind and solar, so much curtailed power, that there's lots of free electricity.
[00:20:22.92] And if you waste free electricity, it doesn't cost the system anything. I was surprised because you keep hearing-- I know how expensive hydrogen is. But yeah, it's expensive until you start seeing what metal air batteries cost and what does lithium batteries cost and all this. So even with today's high costs, if we had to go to a wind and solar dominated system today, a hydrogen storage system would be the cheapest way to firm up system.
[00:20:57.42] Karen Baert: I want to take a step back, talk about your broader career research impact in the space. You've made a tremendous impact as a researcher. Your work has reached over 50k citations. You have an impact factor of around a hundred. For our listeners, that means that your research is very well regarded and a big reference in the scientific community. What has led to that academic success and what gets you out of bed in the morning?
[00:21:22.82] Ken Caldeira: So there's a couple of things there. So one thing is the ability to work mostly with young postdocs. Or I guess you can't say young. You have to say early career. But that it's to come into the office and have a bunch of bright and super motivated people. In most areas, people don't want to talk to people twice their age. Academia is one of the few places where people half your age still feel like, oh, I could learn something by interacting with you. And so it's super fun.
[00:22:01.10] And then the other thing is, I think a big-- I'm basically a happy person. And some people say, oh, you're working on all this miserable-- like, the Earth's falling apart and oceans are acidifying and all this and that. How do you stay happy through all this? And I kind of feel like, oh, that you're just feeling like you have meaningful work, that I get to come into work every day and say, well, what can I do to have the biggest impact that I can have? That's a real privilege. And then the other thing that we get to do, which not everybody gets to do, is we get to play.
[00:22:41.10] So like yesterday, it was like, OK, normally people do electricity systems through linear optimization. So I thought, oh, could we do like just do it through simulation, numerical simulation, not optimization, but just like trying to have little agents deciding what to do? And so I spent the day yesterday prototyping an agent-based electricity system model. It's just like there was no-- it's just like for fun, right? It's just fun.
[00:23:08.81] Karen Baert: I can see the joy on your face when you're explaining this, so I think that's beautiful. And to go back to your first point, an experienced mentor of mine likes to use a metaphor, my mission is putting old heads on young shoulders. It very much reminds me of that when you talk about that.
[00:23:23.21] Ken Caldeira: I actually just did a tweet this morning because in 1990, I was an exchange scientist in what was then the end of the Soviet Union, and I was in the lab of Mikhail Budyko. Mikhail Budyko in the '60s was probably one of the best climate scientists in the world, and into the '70s. And he developed the whole concept of global energy balance that's at the heart of climate models.
[00:23:53.04] But when three dimensional climate models came around and more advanced computers, he was kind of like, oh, I did all that before already then 20, 30 years ago. And I saw, oh, he could have said, oh, modern climate models are based on the concept of energy balance. They're standing on the shoulders of giants. And isn't it nice that what I did has led to this? And that I realized then like, oh man, the next generation is going to win.
[00:24:23.82] Karen Baert: I'd like to end with the question that we ask every guest at the end of the podcast. And it's funny, because you just used the metaphor, actually. I have the strong belief that we all stand on the shoulders of giants who came before us, and to use Isaac Newton's world, standing on their shoulders. It's what makes us see further. In that context, who inspires you most and why?
[00:24:42.78] Ken Caldeira: Well, I would say the person who had the most influence on me is who I consider my scientific father is Marty Hoffert. And Marty Hoffert in the 1980s was the first to integrate Earth sciences with energy sciences, and he had a wind turbine on the roof of a building in New York City that was connected up to electrolyzer, making hydrogen in the early 1980s. And Marty, we co-authored the first paper-- this was in 1998-- to estimate how much carbon emission free power we'd need to stabilize climate.
[00:25:21.01] Marty's been a big proponent of advanced technology paths to addressing the climate problem for decades. And so I would say, Marty Hoffert has had the strongest influence on me. And one of the things that's really nice is I can see Marty's influence on some of my postdocs, so that there-- that there's definitely a legacy of Marty's influence going down another generation.
[00:25:45.84] Karen Baert: Paying it forward.
[00:25:46.98] Ken Caldeira: Yeah.
[00:25:47.32] Karen Baert: Wonderful. Wow. Ken, in one of your previous interviews, you joked about the fact that scientists aren't always the best communicators. If that's true, I think it definitely doesn't apply to you. So thank you so much for the great conversation and for providing this super important bridge between different worlds and making sure that the scientifically valid perspectives are being heard and understood. Thank you for enlightening us today.
[00:26:12.76] Ken Caldeira: Well, thank you very much. This was lots of fun.
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