Estimating the Social Costs of Hydrofluorocarbons, with Lisa Rennels

Notable quotes

• Hydrofluorocarbons have a brief, intense effect on global temperatures: “In contrast to long-lived greenhouse gases like carbon dioxide, hydrofluorocarbons and methane remain in the atmosphere for much shorter periods of time. They exert an impact on temperature for a much shorter time frame. But, that said, while they’re in the atmosphere, they have a much larger impact on temperature than a gas like carbon dioxide … For example, HFC-134a, the most abundant hydrofluorocarbon in the atmosphere, has an estimated global warming potential about 1,500 times that of carbon dioxide over a 100-year period.” (7:11)
• Estimating the costs to society of hydrofluorocarbons: “The model estimates social costs between about $15,000 per ton for HFC-152a to over $2 million for the most potent hydrofluorocarbon … These are values for a ton of gas emitted in 2020. Social costs for a marginal ton emitted later tend to increase in future emissions years.” (17:43)
• Global agreement requires reducing emissions of hydrofluorocarbons: “The Kigali Amendment dictates a few different phasedown schedules for different country groups … Broadly, these requirements range from about an 80 percent reduction by 2045 (the most lenient case) to an 85 percent reduction by 2035. These are pretty strict phasedowns, and admittedly already might be difficult to achieve, but there are substitutes to hydrofluorocarbons and more low global warming–potential refrigerants that some experts think might enable an even more aggressive phasedown.” (21:15)

Top of the Stack

• “The Social Costs of Hydrofluorocarbons and the Benefits from Their Expedited Phase-down” by Tammy Tan, Lisa Rennels, and Bryan Parthum
• “Comprehensive Evidence Implies a Higher Social Cost of CO₂” by Kevin Rennert, Frank Errickson, Brian C. Prest, Lisa Rennels, Richard G. Newell, William Pizer, Cora Kingdon, Jordan Wingenroth, Roger Cooke, Bryan Parthum, David Smith, Kevin Cromar, Delavane Diaz, Frances C. Moore, Ulrich K. Müller, Richard J. Plevin, Adrian E. Raftery, Hana Ševčíková, Hannah Sheets, James Stock, Tammy Tan, Mark Watson, Tony E. Wong, and David Anthoff
• The Impossible Will Take a Little While: A Citizen’s Guide to Hope in a Time of Fear by Paul Rogat Loeb
• Not the End of the World: How We Can Be the First Generation to Build a Sustainable Planet by Hannah Ritchie
• “Are we the Last generation—or the First Sustainable One?” TED Talk by Hannah Ritchie
• The High Sierra: A Love Story by Kim Stanley Robinson

The Full Transcript

Daniel Raimi: Hello, and welcome to Resources Radio, a weekly podcast from Resources for the Future. I'm your host, Daniel Raimi. Today, we talk with Lisa Rennels, a PhD candidate at the University of California at Berkeley, and an Oak Ridge Institute for Science and Education Fellow with the National Center for Environmental Economics at the US Environmental Protection Agency. Lisa is a coauthor on a recent paper that estimates how hydrofluorocarbons (HFCs), an industrial gas used in refrigeration and other applications, contribute to the societal costs of climate change.

In today's episode, I'll ask Lisa to help us understand what hydrofluorocarbons are, how they compare with other greenhouse gases like carbon dioxide and methane, how recent policies will reduce climate damages from HFCs, and a lot more. Stay with us.

Lisa Rennels from the University of California, Berkeley, welcome to Resources Radio.

Lisa Rennels: Thank you. Nice to be here.

Daniel Raimi: Lisa, we are going to talk today about your recent work with colleagues on hydrofluorocarbons, or HFCs. We're going to use that term, HFCs, a lot today. But first, I'd love to ask you how you got interested in working on environmental issues. I know you're sort of a renaissance woman—you have lots of interests and skills—what helped bring you into the field of environmental policy and economics?

Lisa Rennels: I grew up in northern California alongside my twin sister, and I think my parents' go-to solution for the absolute chaos of raising twin toddlers was to take us outside as much as physically possible. We were all over the front yard, my grandma's house in Santa Cruz, Redwood trees, Peninsula Foothills—we just spent a lot of time running around outside growing up. I think that's actually where I gained a lot of my appreciation for the natural world.

Then, more academically, I took an advanced placement environmental studies course as a senior in high school, and I think that really jump-started my thinking about studying environmental issues and thinking more critically about things like climate change. I remember doing a semester-long project where we had to collect news articles and papers in some subtheme of environmental studies that we found interesting. That's actually when I started learning about environmental economics and climate change economics and got really excited about using those types of frameworks and tools—which I'd observed used in other domains to approach environmental policy. That was my start in the environmental economics and climate change economics sphere.

I've been working on environmental issues more or less since then. First, in college, I was a major in environmental studies and focused there on ecological economics and ecosystem services. Then, I worked at an environmental economics consulting firm in Boston. I actually worked on BP oil spill evaluation and also climate change impacts work now and throughout my PhD at the University of California, Berkeley. It's been since I was young, I would say.

Daniel Raimi: That's really interesting. We ask everybody that question when they come on the show, and I think you're the first person, at least that I've interviewed, who got into environmental economics in high school. You're the earliest of anyone, so congratulations.

Lisa Rennels: Thank you. It was just some news article I read, but then I ended up finding a really wonderful advisor in college, and it went from there.

Daniel Raimi: That's really cool. As I mentioned, Lisa, we're going to talk about your recent paper on HFCs, but before we talk about the paper and the social costs of HFCs, let's just do a little bit of background. What are HFCs? How do they function in the economy? What do they do? And why were they invented in the first place?

Lisa Rennels: HFCs are a class of industrial chemicals, and they're primarily used in refrigeration, air-cooling and air-heating, insulating foams, and aerosol propellants. They were developed actually as replacements for ozone-depleting substances. Those were phased out under the Montreal Protocol, which I believe went into force in 1989. The substances controlled by that protocol either contained chlorine or bromine, which HFCs do not contain. They were basically a replacement for those ozone-depleting substances.

The phaseout of ozone-depleting substances motivated a very rapid adoption of HFCs as a replacement and widespread adoption of interior space-conditioning, and foam building insulation also contributed to that increased use. A little bit tangentially, but relatedly, experts are now forecasting that global warming will exacerbate and accelerate the demand for cooling products around the globe. As temperatures increase, air-conditioning and other cooling technologies are going to be a very important adaptation strategy to cope with heat. There's a lot of literature surrounding the projections of what increased adoption of these cooling technologies will mean and what those potential impacts are.

An example folks might've heard of is that increased energy use for air-conditioning, if fossil fuel–generated, could in turn contribute to global warming and create a feedback loop.

Somewhat similarly, HFC emissions from those same cooling products have potentially serious side effects for climate change. In 2018, a report called the Scientific Assessment of Ozone Depletion reported that HFC emissions increased by 23 percent over just four years, from 2012 to 2016. It's really predicted that there will be escalated growth over time, especially in developing countries, as adoption of these cooling technologies continues.

Daniel Raimi: That's really interesting. HFCs—I feel like there's multiple layers of ironies to them. One is the feedback loop that you mentioned, and the other is the fact that they were invented to solve an environmental problem, and then they've sort of created a new environmental problem.

Lisa Rennels: Yes, that's absolutely correct.

Daniel Raimi: Some listeners are probably aware that HFCs often have really high global warming potentials. That just means that, on a pound-for-pound basis, they trap much more heat during their lifetimes than carbon dioxide. But can you help us understand that a little bit more, Lisa? Can you give us a sense of how HFCs are currently contributing to the warming that we're experiencing today and how they might compare with other gases like carbon dioxide or methane?

Lisa Rennels: Sure. As you said, HFCs are a very potent greenhouse gas, and they contribute to climate change and have the potential to contribute quite a bit more in coming decades. The phaseout of ozone-depleting substances, I have to say, was really important and definitely shouldn't be understated. But now, we're faced with this sort of irony that you just mentioned. Now, we need to handle the high global warming potential of these HFCs.

Quickly, there's just a few interesting characteristics of these gases that I think are worth mentioning to characterize how we think about their contribution in the future.

First, there's what is referred to as “short-lived” greenhouse gases. In contrast to long-lived greenhouse gases like carbon dioxide, HFCs and methane remain in the atmosphere for much shorter periods of time. They exert an impact on temperature for a much shorter time frame. But, that said, while they're in the atmosphere, they have a much larger impact on temperature than a gas like carbon dioxide. We see this when we compare what we call “temperature impulse responses,” which is the response of the global temperature to a pulse of a greenhouse gas emission. The global warming potential that you mentioned takes these two elements into account over a predefined period.

For example, HFC-134a, the most abundant HFC in the atmosphere, has an estimated global warming potential about 1,500 times that of carbon dioxide over a 100-year period.

Then, one last important point here is that while carbon dioxide is emitted from activities like fossil fuel combustion that happens all at once, HFCs are integral components to technologies like air-conditioners, and they tend to leak out slowly over time at a much lower rate. These different factors are relevant when we try to project their emissions and the impacts on climate change.

Taking that all into account, HFCs are predicted to warm the earth a bit less than 0.5°C by 2100. To contextualize that, we're trying to stay below this Paris 2°C target. A bit less than half of a degree by 2100 is a pretty big deal.

That said, there's quite a bit of variation in these predictions, because it depends on projections of adoption, technological shifts, policy, and more. There's always a range.

But global warming agreements like the Kigali agreement, which I'll talk about later, are predicted to avoid much of this warming. I think Kigali is predicted to avoid about 0.2°C–0.4°C.

We don't need to go into this and we don't go into it in this paper, but I thought it might be worth mentioning that there are really interesting active discussions about how to prioritize and handle long-lived gases versus short-lived gases, especially in light of different policies and in light of the conversation currently around carbon dioxide and methane. If listeners are interested, I think that's a kind of interesting space right now.

Daniel Raimi: It is super interesting, and as someone who's worked on methane a little bit over the years, it is a rich and complex and sometimes contentious conversation, but we'll save that for another day.

Let's talk now about what you and your coauthors find in this paper, and just so people can find it easily, the name of the paper is “The Social Costs of Hydrofluorocarbons and the Benefits from their Expedited Phasedown.” It's in Nature Climate Change. And, of course, we'll have a link to it in the show notes, so people can easily get to it.

Listeners of this show have heard a lot about the social cost of carbon, so we don't need to go into a lot of detail about what social cost means. But really quickly, can you just remind us what we mean when we say the social cost of HFCs?

Lisa Rennels: Sure. The social cost of HFCs, or more broadly, the social cost of a greenhouse gas, measures the monetized net present value of the damages to society caused by an incremental metric ton of gas emissions. So, these social costs are a key metric to informing climate policy, especially in the United States. In particular, the estimates for carbon dioxide and methane are the most active in the US government regulatory space now and are used by the government and other decisionmakers in benefit-cost analysis and have been for over a decade now. The models used to calculate these social costs draw on quite a few disciplines, including climate science, economics, demography, and several others.

Daniel Raimi: Great. The components of the social costs vary widely, right? There are damages that society experiences from things like sea level rise and higher temperatures and the effects on mortality and so on, right?

Lisa Rennels: That's correct. You can estimate these in several ways, but there are definitely several different sets of damaged channels. From an economic standpoint, we often refer to two categories of them—market and nonmarket. But yes, there are quite a few channels, some of which are captured better than others, and there's quite a bit of ongoing work on that.

Daniel Raimi: Great. We'll just refer people to previous Resources Radio episodes on the social cost of carbon, of which there are at least two or three.

Now, another final background question, before we get to your results. Could you give us a high-level overview of some of the methods you use to calculate the social costs of HFCs? There's a ton of detail here, and it's super rich, and interested listeners should go to the paper and go to the appendices, but if you could give us a high-level overview, that would be great.

Lisa Rennels: As I mentioned, the models we use to calculate these social costs integrate several disciplines, and they're called “integrated assessment models,” or more specifically, “cost-benefit integrated assessment models.” They integrate these different disciplines together into one model and estimate the net present value of the marginal impact of emitting one ton or some pulse of a greenhouse gas into the atmosphere. I won't bore you with all the details—those are in the paper—but broadly, I would say there are a few steps to this calculation.

First, we estimate the model under a baseline-emissions scenario, and that means we calculate the baseline damages from climate change under some assumed baseline policy scenario.

Then, second, we add a small, marginal emissions forcing for a given HFC of interest to the model's emissions-forcing projection. We basically say, “Plus pulse in 2020,” and then we reestimate the model to compute damages in that sort of perturbed scenario. To be a bit more concrete there—adding a pulse of emissions creates a marginal increase in radiative forcing, which creates a marginal increase in atmospheric and ocean temperatures. That in turn impacts the economy along several channels, like we discussed before. We're really trying to estimate the impact of those marginal emissions on the economy.

To do so, we compute the social cost of an HFC as the net present value of the difference in damages or the marginal damages between the baseline and marginal emissions scenarios. I'll just note quickly that this differs from using a global warming potential method. That generally focuses only on the climate-science component of the process. It measures how much energy the emissions of one ton of a gas will absorb over a given period of time and then creates a ratio relative to one ton of emissions of carbon dioxide. That heuristic can be used to scale the social cost of carbon to come up with a social cost of HFCs or for any greenhouse gas that has an estimated global warming potential without doing this full, direct calculation that we outlined here. But that method has been used quite a bit historically.

Daniel Raimi: Right. Lisa, this is an extra question that I hadn't planned on asking you, but I'm wondering if you can say a little bit more about what additional benefits to policymakers it provides to actually have a social cost estimate relative to just a global warming potential estimate? Why is it differently useful to have this type of figure?

Lisa Rennels: I think there are a few reasons, and there are pros and cons to both approaches. But in this case, one of the pros is that this direct calculation approach is the way that we currently calculate social costs for other gases like carbon dioxide, nitrous oxide, and methane. Using this similar methodology is valuable, because it helps us compare these different social costs more accurately instead of using one method to calculate one set of them and a different method for the other set.

More complicated, but also a very interesting literature, is that there is a kind of systematic difference between using only the climate-science side or this contribution to the energy balance versus including damages and economic modeling. For example, that includes thinking about things like the discount rate, damages over time, adaptation, and just a richer literature of how emissions impact social systems. I think there's a lot of value in understanding that and also a lot of value in literature that simply compares what the two results show and sort of decomposes why the results might be different.

Daniel Raimi: That's great. I'll ask you in a few minutes to help us compare those results. But first, let's focus on the social costs. What are some of the estimates that you and your coauthors come up with the social costs of HFCs, and how do they compare with other gases like carbon dioxide and methane?

Lisa Rennels: Sure. Overall, we find some very large numbers. Given what we just talked about, this is perhaps expected, given the potency of these gases. But in this paper, we are able to, as I said, directly calculate the social costs under several different modeling frameworks, which I'll go into. Then, we can later show what these costs generate in terms of climate benefits from proposed emissions-reduction schedules, which I think is a really valuable contribution to putting a dollar value on the benefits of phasedowns and global agreements.

As a concrete example, the recent literature calculates the social cost of carbon dioxide to be around $190 and the social cost of methane to be around $1,600. We find that HFC-134a, which is the most prevalent in the atmosphere, is estimated to have a social cost of $144,000, using the same model and the same near-term target discount rate.This is dollars per ton in 2020 US dollars for a pulse of emissions in 2020.

Taking the full suite of HFCs, it does vary. The model estimates social costs between about $15,000 per ton for HFC-152a to over $2 million for the most potent HFC. As I said, these are values for a ton of gas emitted in 2020. Social costs for a marginal ton emitted later tend to increase in future emissions years.

To dive a little bit deeper, we actually present results for two different modeling frameworks. The first framework is historically used by the US government, and it harmonizes three prevalent integrated assessment models to get a single result. Then, the second leverages a newer model that incorporates several significant advancements in the scientific literature and was recently used in a set of proposed updated estimates by the US Environmental Protection Agency.

Sticking with HFC-134a, the first modeling framework estimates the social cost as $96,000 per ton, while as I said, the second estimates about $144,000 per ton, so that's a 33 percent increase from an older modeling framework to a newer one. I can dig into the reasons for that later, if we have time.

Finally, we compare these results to estimates produced using global warming potentials from the literature. Those, as I said, are used to scale the social cost of carbon dioxide and produce social costs of HFCs.

There's quite a bit of literature, as I said, comparing these two. So, we contribute to that. We find that the two approaches do not produce the same values and that the nature of the difference between our modeling and the global warming potential approach is fairly uniform across gases, but it's model specific. Depending on whether you're using the older modeling framework or the newer one, you're either overestimating or underestimating compared to global warming potentials.

Daniel Raimi: Interesting. The newer modeling framework tends to produce higher figures than the global warming potential, and the older modeling framework tends to produce lower figures? Is that right?

Lisa Rennels: That's correct.

Daniel Raimi: Interesting. Lisa, as you mentioned, you and your coauthors estimate the social benefits of the Kigali Amendment, which I think is sometimes called the Kigali agreement. I'm not quite sure which term is right; maybe you can help me sort that out. But some listeners probably know some details about the Kigali Amendment, but for those who don't, can you give us a thumbnail sketch of what it is and then what types of benefits it would provide if it were fully implemented?

Lisa Rennels: I run into this confusion, as well. I believe it is formally the Kigali Amendment, but I've seen it referred to as the Kigali agreement, as well, so either works.

But starting with a little bit of background on that amendment, in recognition of their potency as a greenhouse gas, the 1997 Kyoto Protocol, under the 1992 United Nations Framework Convention on Climate Change, included HFCs as a regulated substance. While they were included there and noted for their potency, that Kyoto Protocol includes HFCs only in their enforcement of total limits on greenhouse gas emissions, but it doesn't specifically control HFC emissions. HFC emissions are explicitly controlled under the Kigali Amendment to the Montreal Protocol, and that came into force in 2016. They haven't been explicitly controlled for very long.

The Kigali agreement provides specific targets for the phasedown of HFCs and is expected to avoid an increase in atmospheric temperatures of between 0.2°C and 0.4°C by 2100. Although, as I said, those estimates are subject to lots of assumptions, so they can range.

The Kigali Amendment dictates a few different phasedown schedules for different country groups, which I won't go into detail about now, but broadly, these requirements range from about an 80 percent reduction by 2045, at the most lenient case, to an 85 percent reduction by 2035. These are pretty strict phasedowns, and admittedly already might be difficult to achieve, but there are substitutes to HFCs and more low global warming–potential refrigerants that some experts think might enable an even more aggressive phasedown.

Considering that and the literature, we also assess the benefits under a more ambitious timeline, which we'll refer to as the “maximum technologically feasible reduction schedule.” MTFR is what I'm referring to when I say that. That entails a full phaseout by 2035—even more ambitious.

For a few numbers, we first estimate a range of total climate benefits based on the methods from the US government historically—that first modeling framework. Those range from $16 trillion total under the Kigali phasedown schedule to $18 trillion under the expedited phasedown schedule. Those are already some pretty big climate benefits.

But if we move to the more recent modeling framework that was published in 2022—this is one of the three models that incorporates more recent scientific literature and is used by a recent proposed EPA rule—the benefits jump quite a bit and range from $37 trillion under the Kigali agreement to $41 trillion under the expedited phasedown.

Under both of those frameworks, we're estimating an additional 11 to 12 percent, maybe, in climate benefits from adopting a more aggressive global phasedown schedule. Overall, there are just some really, really high climate benefits from these agreements.

Daniel Raimi: I was just doing some searching as you were sharing those numbers, and another point of context is that the entire US economy in 2021 had an output of about $23 trillion. In the ballpark of the entire US economy. So, those are big numbers.

Lisa Rennels: They are really big numbers. They're quite a bit bigger than certain other climate benefits we've calculated and certainly are impressive.

Daniel Raimi: Lisa, I'm curious, before I ask you another modeling question, can you say a little bit more about the substitutes that are available for HFCs, their costs, and whether that's something that you and your coauthors take into account in developing these estimates? Are we ready to go with cheap alternatives, or is there still work that needs to be done to bring those costs in line with current costs of HFCs?

Lisa Rennels: That's a great question. I have to admit, this is not my area of expertise in this paper. I would refer you to my coauthor who worked mostly on this expedited phasedown.

But what I do know is that there are HFC substitutes referred to as “HFOs,” and there are also low global warming–potential refrigerants. Ammonia is one of them, and so is carbon dioxide, actually. Perhaps another irony coming full circle there. Then, you can also use HFC combinations. While you're still using HFCs, you might be able to shift simply away from the extremely high–global warming potential HFCs.

But I think that's a really good question about the costs and technological feasibility. I believe, in the paper, we refer to the literature that we use to estimate these maximum technologically feasible solutions that would include more details there.

Daniel Raimi: Great. Definitely another opportunity for people to look at the paper.

Lisa, one last question I'd love to ask you before we go to our Top of the Stack segment, which is asking you to get into the weeds and get a little wonky and talk about the different modeling frameworks, which you've already mentioned. But I'm curious if you could say a little bit more about some of the recent advances in climate economics that are incorporated into the updated modeling framework you use, which I believe is called Mimi-GIVE, and maybe you can tell us where that name comes from. Help us understand how that change in methodology leads to these different results. I'm also curious if you think of whether they are qualitatively better than previous estimates, or if they're just different.

Lisa Rennels: Sure. I'll try to hit those points. Let me know if I miss any of them.

Mimi-GIVE is referring to this second modeling framework that I've mentioned over the last parts of this podcast. For a bit of history, which I think you might've mentioned in previous podcasts, but the National Academies of Sciences, Engineering, and Medicine conducted a comprehensive review of social cost of carbon dioxide estimates and issued a final report in 2017 that recommended specific criteria for future updates of how to estimate the social cost of carbon dioxide, and it also detailed a modeling framework that would satisfy those criteria. This also included both near-term updates—so, things that were predicted to be able to be done in the near term—and then also longer-term research and longer-term updates pertaining to various components of the estimation process.

To break down the term, the GIVE model, the Greenhouse Gas Impact Valuation Estimator, is the model that was recently published in Nature in 2022 that incorporated quite a few updates; in fact, I think it included all of the near-term updates listed in that report. Then, Mimi-GIVE—Mimi is the framework that these are built upon. That's actually a software framework that was developed between Resources for the Future (RFF) and the University of California, Berkeley, that has been meant to enable building integrated assessment models, comparing them, running uncertainty analysis, and just leveraging the skills of different researchers to bring people together to create new integrated assessment models.

We find that the results, both in terms of the social costs of individual gases and in terms of the total climate benefits of the HFC phasedown are quite a bit larger under this new modeling framework, which was somewhat expected, because recent updates have shown that including all of this comprehensive evidence also shows higher social costs of carbon and higher social costs of methane. These increased costs are a product of this new modeling framework.

In terms of different pieces, we attribute the upward shift in estimates to quite a few different components; in particular, advances in climate system representation. A better, more accurate representation of that aforementioned temperature impulse response, or how the climate responds to an impulse of emissions. More accurate characterization of damage pathways. There's very rich literature on damages and impacts to the economy from changes in temperature, and those are folded into these new models. Then, probabilistic socioeconomic projections—so, a new approach, and a new set of projecting GDP, population, and emissions into the future. Finally, improvements to the discounting module, which adopted a growth-consistent Ramsey framework, so a different sort of approach than constant discount rates and also just a lower near-term discount rate. It went from 3 percent to 2 percent, which is also what is suggested by a recent Circular A-4, from the US Office of Management and Budget.

All of these different components contribute to the increase, and I think a more quantitative breakdown is shown in that Mimi-GIVE paper.

Daniel Raimi: That's great. That's the Rennert et al. paper led by our colleague, Kevin Rennert at RFF, who we featured on the show, as well.

Well, Lisa, this has been a fascinating conversation. I've learned a lot, and I'm sure our listeners have, too. I'd love to ask you now to recommend something that's at the top of your literal or metaphorical reading stack. It can be something that you've read or want to read or something you've watched or heard; it can be related to the environment or not. We're not very picky. What is at the top of your stack?

Lisa Rennels: I have to admit, I listen to this podcast a lot, and I like using this question to add to my stack. I'm always very impressed with people reading different informational and academically relevant books. I have to admit that a lot of the books I've been reading lately are more in the vein of the psychology or mental aspects of environmental work, or just books that are celebrating aspects of the natural world. For me, I find that those balance out the day-to-day academic articles and focus on climate change. I'll mention a few of those.

I just finished reading a book called The Impossible Will Take a Little While: A Citizen's Guide to Hope in a Time of Fear. It's by Paul Loeb. It's not explicitly focused on environmental issues, but it does feature them quite prominently. It's a collection of stories and essays focusing on people and movements in the past, specifically in situations where people have faced seemingly impossible or very difficult odd and how they find hope and strength and persist through them. For me, I think it just holds really valuable lessons for people like myself, working on kind of existentially scary topics sometimes, but it’s also relevant for non-environmental social movements. I tend to just find that looking back into history to find examples of people who have faced existential odds or really intense, challenging problems can be really useful. I've loved that book. Highly recommend it.

Daniel Raimi: That sounds so interesting, and I just searched for it really quick, and apparently that title, The Impossible Will Take a Little While, is borrowed from a Billie Holiday lyric.

Lisa Rennels: Really? I've actually been wondering. All right, now I learned something.

Daniel Raimi: That's what the internet said.

Lisa Rennels: I believe you.

Daniel Raimi: Hopefully, the internet is right.

Lisa Rennels: That's a great book.

I have two more, maybe. Up next I'm hoping to read Hannah Ritchie's Not the End of the World. I guess there's a bit of an optimism or persistence theme, here. I can't say much about that book, because I just started it, but I've heard great things, and I also really enjoyed her recent TED Talk. It's about a 15-minute TED Talk, but I really enjoyed it, and it motivated me to read the book.

Then, one more that I'm actually just staring at on my desk is a book called The High Sierra: A Love Story. It's by Kim Stanley Robinson, who's the author of Ministry for the Future. That's a popular book right now that folks might've heard of in the environmental and climate theme. But this book is just this very kind of raw, beautifully written book about the California Sierra Nevada mountains, and it traces the author's exploration of them and his adoration of these mountains throughout his life. It's been fun for me, because I grew up in California. It really does kind of read like a love story, and it makes you want to just drop everything and go hiking, which is frustrating at times but also fun.

I've found that it's this nice reminder of these parts of the natural world that we kind of grow our identities around and are really tied to that can be really needed escapes from work, but simultaneously really strong motivators for our work, which comes back to growing up in nature and in California and something that motivates me and also provides a lot of relief. I think that it is a great book that I highly recommend and has some really beautiful photographs, as well.

Daniel Raimi: That sounds lovely. We actually interviewed Kim Stanley Robinson on the show about two years ago, I think, shortly after Ministry for the Future came out.

Lisa Rennels: I'll have to listen to that one.

Daniel Raimi: It'd be really interesting to read his newer work.

Well, Lisa Rennels, one more time, thank you so much for coming out to the show and helping us understand HFCs, their social costs, and how policy can help reduce them. We really appreciate your time.

Lisa Rennels: Thanks so much.

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