 Good afternoon and welcome to today's energy seminar. Today we have with us our very own Chris Field, who's the Perry McCarty director of the Stanford Woodson Institute for the Environment and the Melvin and Joan Lane Professor of Interdisciplinary Environmental Studies. Here at Stanford, prior to that, he was a staff member at the Carnegie Institution for Science and founding director of the Carnegie's Department of Global Ecology from 2002 to 2016. And on a more personal note, I think we all know Chris, a great gratitude for his willingness to take on many leading science positions and administrative positions for the science community. In particular, he's been a great colleague in the Stanford Energy Environment community for many years, an outstanding member of the international scientific community. And last but not least in my case, a stand-up, a very influential person in the affairs of the Intergovernmental Panel on Climate Change. And today he's going to talk on a subject he'll probably tell you, I don't know anything about it, subject that I think I do. And I've probably learned as much or more from him than anybody else. And his topic today is biomass energy and natural climate solutions, a meaningful piece of the solutions portfolio, a very important and timely topic. Chris, take it away. Well, thank you so much, John, for the introduction and the chance to share some thoughts with all of you. I want to be clear up front that my bottom line is in the title. We live in kind of an all-in society and it's always a challenge to present a nuanced picture that says this is a topic that has some really compelling advantages, but it also has some compelling disadvantages. And that's going to be the message that I'll be leaving all of you with today. Let me start out with just a comment on the role of biomass in our current energy system. We tend to think about the idea that we live in a fossil economy, but it's important to remember that all that fossil fuel used to be biomass at some point. And it actually was really a lot of biomass. Jeff Dupes did a really wonderful study of this almost 20 years ago now, where he calculated the efficiency with which organic matter was converted into fossil fuels. And his conclusion was that producing a single gallon of gasoline required about 90 tons of ancient plant matter. And if you scale that up to the scale of today's current energy system, what you come up with is that the fossil fuels that we burned a couple decades ago contained the equivalent of 44 hexagrams of carbon more than 400 times the current annual primary production of the planet's current biota. So we're drawing on buried sunshine. We run a biomass economy now, not a fossil fuel economy. But it's one that requires many, many years of primary production in order to get a single year of fossil fuel reserves. There are a lot of compelling reasons to think about biomass, playing a bigger role in the energy mix. And I'll be dealing with each of these in sequence. The first one is that biomass accounts for really big fluxes in the carbon cycle, big relative to fossil fluxes. Also plays a major role in emissions of greenhouse gases other than CO2. Biomass provides some uniquely compelling options for producing liquid fuels compared to a lot of the technology options that are on the horizon. Most of the things involving biomass are relatively ready to go now. Biomass provides some of the few options for generating negative emissions, for removing CO2 from the atmosphere. And when we start talking about negative emissions, we also begin to relax the constraints on timing of the solution, and we can emit now and draw down later, which provides some profound economic advantages. And then finally, solutions involving biomass can have profound co-benefits, co-benefits in terms of the conservation agenda, or in terms of building strong economies. But there are a lot of reasons to be worried about biomass as well. And probably the most important, the overwhelming one is that growing biomass requires massive amounts of land. There are always speculations about, well, couldn't we use marginal land or desert? And the answer in general is no. Producing large amounts of biomass requires large amounts of good land, abundant water, and fertilizer. Sometimes biomass energy has questionable mitigation benefits. That's been especially the case with ethanol from corn, where the natural gas inputs for grinding and drying and processing the corn often amount to about as much energy as the ethanol output you get. It's also really challenging to account for the indirect consequences of whatever we do when we allocate an acre to corn production for biomass. Does that mean that now the demand for corn has gone up and another acre gets deforested? And are we accounting for that properly? It's also important to remember that this possibility of separating emissions and removals in time can be regarded as a license for delay. In some ways, it's a strategy not only for giving us a little more time flexibility, but for kicking the can down the road in terms of solutions. And we want to make sure that we're not thinking about embracing biomass as a way to avoid responsibility. And finally, it's important to recognize that a lot of the solutions that result in an increase in biomass and a decrease in carbon in the atmosphere may not be permanent. It may be that we're solving a problem in one place, only to have it come back later, or that we're solving it in one place only to have it come out in another part of the earth system. So big issues that need to be dealt with. Before we talk specifics, I want to just go through a couple of the numbers that are good to keep in mind. The first is that most of the material that I'm going to talk about today is going to be in gigatons of CO2, a gigaton and a pedogram, or the same thing, a billion tons, or 10 to the 15th grams. I'm going to present material that's mostly in units of carbon dioxide. Conversion between carbon and carbon dioxide is simply the ratio of the molecular weights. But you see the numbers both way and from a biosphere perspective, the units that make the most sense are the carbon ones, but the units that we talk about in the context of solving the climate problem are usually the CO2 ones. In converting from biomass to carbon is relatively straightforward. Most biomass is about 50% carbon. And the energy content of dry biomass is kind of in the middle of the range for decent coal. That's about half of the energy content of oil or natural gas. The second set of numbers I'd like everybody to keep in mind as we go through the details is the amount of area that's required. So the total ice-free land area of the Earth is a little under 15 billion hectares, about 2 and 1 half acres. About 10% of that is cropland now. About 20% of it is grazing land. And when we start talking about deploying new kinds of solutions at the scale of a billion hectares, we're talking about deploying at the scale of current global agriculture. An important constraint that I want to make sure everybody has in mind when we talk about biomass is that the efficiency with which sunlight is converted into biomass energy usually is less than half a percent. And so when we're comparing biomass-based technologies with industrial technologies, we need to deal with this really low efficiency. And we also need to deal with the really large amounts of water that are required to grow plants. And a typical number is that it takes about 500 units of water to produce one unit of plant. Before we talk details, I want to just make sure everybody's up to speed on a couple of important features of the global carbon cycle. We all think a lot about the emissions of CO2 from the combustion of fossil fuels and from deforestation. But it's important to recognize that photosynthesis online is a very large flux relative to either of these. It's approximately five times the size of the fossil flux is the global annual plant growth on land. But that's not a net uptake, because on an annual basis there's also a comparably sized release from land in respiration and fire. So the average annual land balance in recent years has been the sum of these emissions and the uptake. Just to complete the picture, on the oceans we have a similar large amount of CO2 dissolves in the oceans on an annual basis. And a comparably large amount is released. But they're not exactly the same. And so there's a net sink in the oceans that in recent years has been around 9 billion tons of CO2 per year. It's important to recognize that these two net fluxes, the sink in the oceans and this sink on natural land, are really big free subsidies that we receive from nature for free now. And when we look at solving the climate challenge, preserving those two fluxes to the largest extent possible is one of the key opportunities we have and one of the key responsibilities. And when we add up all these fluxes in the global carbon cycle, the overall net is the sum of the emissions from fossil fuels and land use change, plus the sinks on land and in oceans, so that the atmosphere currently on an annual basis is gaining about half of the total emission from fossil fuels and land use. And so the airborne fraction is about 50%. The final piece of setup that I want to provide is zeroing in on where the emissions are coming from. As you know, about three quarters of recent emissions come from the energy sector. And the remaining quarter comes from agriculture, forestry, and other land use, what's awkwardly called afolu here. And industry and waste with industry being particularly steel and cement manufacturing. If we dive in in a little more detail, this ag and forestry sector includes several really important fluxes from livestock rearing, agricultural soils, methane emissions from rice, deforestation, and cropland soils. And when we think about deploying biomass solutions, a lot of the solutions are in the spirit of decreasing these emissions from agriculture, forestry, and other land use. Now when we think about constructing solutions to the global climate problem, it's important that we think in budget mode. We know there's essentially a linear relationship between the total amount of carbon dioxide since we started emitting carbon dioxide and the total amount of warming. And that warming is essentially forever so that we know the emissions through 2019 have been a little over 2,300 billion tons of CO2. If we want to have a 66% probability of limiting warming to 1.5 C or less, we've got about a little less than 2,800 billion tons of total capacity. If we move that to 2C, it goes to about 3,540 billion tons. So the overall math is that if we want to have a 66% probability of limiting warming to 1.5 C, the remaining budget is order of 500 billion tons of CO2. A 66% probability of limiting to 2C is order 1,200 billion tons of CO2. And if you simply divide the 2019 emissions into those numbers, you can see that we have very little time left without the budget being exhausted. For that 1.5 number, it's less than a decade. For the 2C number, it's on the order of 2 to 3 decades. It's obviously the reason that there's so much emphasis on the timing of tackling the climate problem. But it's also an important reminder of why negative emissions in the future could be important. They provide the opportunity of exceeding the budget and then backing down to meeting it at a later time. Exactly what time we want to meet it is not determined anywhere in policy. So when we look at how we might achieve that in terms of an emissions trajectory, I'll think in terms of business as usual and then cutting our emissions through the century. But it's important to note that there are some CO2 emissions that are really difficult to decrease. And there are some emissions of other greenhouse gases that are difficult to decrease. And if we want to get to zero, as is required by the budget, we need to come up with some way to generate negative emissions either with an industrial process or a biological process so that we can start generating negative emissions in the relatively near term and make the whole economy go net negative sometime in the 21st century. So that a trajectory for a 2C might look like this with a building pool of negative emissions starting in the near term. And a trajectory that gets us to 1.5C requires an even bigger pool of negative emissions and a transition to making the global economy net negative closer to mid-century than at the end of this century. This challenge of negative emissions has really shaped a lot of the discussion about climate change solutions. And if you ask how much we're talking about, the interquartile range for the recent IPCC special report on 1.5C is 600 to 1,000 gigatons of CO2. Negative emissions removed from the atmosphere between now and 2100 more than the total remaining budget for 1.5C. And there are lots of approaches we can use for this. We can use industrial approaches, geological, oceanic, biological are combined, but that we've got to think about it both for generating net negative emissions across the whole economy and for offsetting the difficult to reduce or intractable emissions from things like steel or cement manufacturing, methane or nitrous oxide from agriculture. Negative emissions have also come into focus because at least in principle, a lot of the options are ready to go technologically and look like they're likely to be affordable. I do wanna emphasize though that this issue of a temporal disconnect is really a slippery slope and there's nothing in any international climate negotiation that says when we would get back to our target and there also is nothing that intrinsically holds the feet to the fire of countries, companies, emitters that really encourages, strongly encourages, requires a linkage between delaying emissions now and really being serious about negative emissions in the future. It's one of the big liabilities associated with the biomass solutions that generate negative emissions. So there are really three ways you can get to negative emissions. The one is using the land and ocean, amplifying the kinds of sinks that we already talked about. The second is biomass energy with carbon capture and storage where the basic idea is growing biomass removes CO2 from the atmosphere. The biomass is converted into electricity in a power plant producing CO2 which is then grabbed and compressed and injected into a geological storage, producing electricity as a consequence of the way the operations managed. And the other technology option is direct air capture where the basic idea is that CO2 is stored in a chemical solution captured from the atmosphere, put in a chemical solution, released from the chemical solution, compressed and pumped into a geological reservoir with a net input of electricity. Land and ocean sinks are something that happen all the time and we know how to manage them. BEX involves relatively simple technologies that we think we know how to do and direct air capture involves a combination of things that are a variety of different levels of technology readiness. The pictures of what these look like is that grown forests and we really know how to do direct air capture. We're beginning to see deployed at the something between the laboratory and the full industrial scale and biomass energy with carbon capture is beginning to be deployed at approximately the million ton scale, so commercial but not transformative of the earth system. When we look at the way the carbon cycle is envisioned in the future, most of the thinking is around very large amounts of negative emission. This is an example from Shell's sky scenario, which is there to see scenario. And you can see the combination of very large amounts of energy from biomass and substantial amounts of negative emissions here showing something over 10 billion tons per year of negative emissions with CO2 captured either from the air or from smokestack emissions and injected into geological reservoirs. So the idea that we solve the problem on the back of large amounts of negative emissions really key to the thinking and key to the way we process biomass energy going forward. So what are our biomass options? There are lots when we think about and there are two main flavors of biomass for climate solutions that I wanna talk about. The first is biomass as an energy source where we're harvesting biomass using it for energy and either doing that as a low CO2 or a no CO2 option depending on whether we capture the CO2. The second is enhancing natural sinks or decreasing releases from natural ecosystems. For biomass energy, we can look at lots of sources from waste, from good stewardship, for example, removing excess fuels in wildfire areas or dedicated biomass. And most of the thinking in recent years has been about dedicated biomass crops, but I think that there are many not yet developed opportunities in the good stewardship and in the waste biomass. When we look at natural climate solutions, there are two important pathways we need to think about. One is pathways that slow emissions that are already occurring that account for that 5.3 billion tons of net land use, things from deforestation, peatland degradation. And then there are lots of ways to increase the sinks that are already an important part of the carbon cycle but can become even more important as a result of investments in improving forest management, expanding forest areas and improving the way we manage soils. I'm gonna go through a number of specific results now, many with colleagues from my own lab and I'm gonna give credit to the people who have contributed to all those studies over more than 20 years now. So the first topic I wanna talk about is biomass for liquid fuels which in the US is primarily liquid fuels from corn. It's an example of a way that progress toward biomass energy has really been driven by policy incentives that are totally separated from protecting climate. It's really important to remember that the reason we have a blending mandate for ethanol in gasoline is as much to do with the calendar of presidential primaries as it is to do with anything else. The renewable fuel standard is a part of both the Energy Policy Act of 2005 and the Energy Independence and Security Act of 2007 in 2017, which is last year for which I could find information, 9.2% of the gasoline sold in the US was ethanol and it consumes about 40% of the US corn crop. The thing that's really tricky about the way we produce ethanol now is that it really has questionable emissions reductions. The big controller on whether or not you get any emissions reductions in production of ethanol from corn grain is whether the grain is dried using natural gas or not. If it's dried using natural gas, you often have greater CO2 emissions in the production of the ethanol than you save by offsetting the gasoline. But with the most modern available techniques, there is a modest amount of emissions reduction that the real advantage of using ethanol for transportation fuel in the US until now has been a way to convert a gaseous fuel, natural gas, into a liquid fuel that burns in the current fleet of vehicles. There also is the potential for dramatic improvements in the emissions reduction from ethanol with advanced techniques for producing cellulosic fuels, but those have been slow to come online, partly because of the incentives haven't been terribly strong and partly because of complicated biochemistry and technology. A dozen years or so ago in my lab, Elliot Campbell said, well, if we're gonna use corn for transportation, should we be using it to make ethanol? And Elliot did a study where he said, okay, let's take the 2008 technology for making ethanol and the 2008 technology for electric vehicles and just ask about transportation efficiency. How many miles per acre you get if you convert biomass into ethanol versus converting biomass into electricity and charging the batteries in an electric car? And back in 2009, what Elliot concluded was that the ethanol pathway gives you about 8,000 vehicle miles per acre. And even in 2009, the bioelectricity pathway gave you almost twice as much transportation output per acre of dedicated land. So even then with the primitive status of the available electric vehicles, it wasn't that we got a technology advantage from producing ethanol, it was that the existing fleet was of internal combustion vehicles. And that was where the demand was. And now that we have a compelling set of electric vehicle options, the motivation for using ethanol for at least for light vehicle transportation is getting to be less and less. It's worth asking whether or not we might wanna continue to use liquid fuels from biomass for aircraft transportation, which is the main transportation area where there are not electrification options. Let me talk for just a couple of minutes about how much biomass we might get for bioenergy. And one way to do that is to ask how much land is available that we're not using for something else. So it's hard to figure out how much land we've got that we're not using. We have pretty good maps of the land that we use for crop and pasture. And I already told you the areas that are involved with those. And we have a pretty good record of where cropping and pasturing uses have been over the last couple of centuries. And so that allows us to make a pretty decent map of where land has been abandoned. And one of the things that's striking me if you look at the map of abandoned cropland is that the eastern half of the US is one of the only areas in the world where there was a wholesale movement of cropland agriculture from one area to another when agriculture shifted basically from New England to the Great Plains. Anyhow, with these maps of abandoned crop and agriculture and pasture, we can say, okay, well, how much plant material could you have grown in those areas? And then what could you get in terms of biomass energy from that? And if we look globally, it turns out that the amount of total global primary production in croplands about 6.8 billion tons of carbon per year, 11.6 in pasture land and about 3.3 of that is in abandoned areas. But a lot of those abandoned areas have now returned to forest or in cities and they're not available for use. So about 1.2 billion tons of carbon is potentially available from abandoned lands that we could use for biomass energy. If you convert that into the amount of energy, you get 16 exajoules, about 2% of global primary energy and 4.4 billion tons of CO2 removal per year. It's a meaningful contribution, but it certainly doesn't come anywhere close to the levels that would be required in order to meet the negative emissions goals in the IPCC 1.5 degree scenarios. One interesting sort of lead on from this question is there enough land available is to say, well, what would it look like if we use that for BEX for biomass energy with carbon capture and storage? And Peter Turner led a study on that in 2018 where he took an approach that was similar to what we had done a decade earlier for saying, well, let's focus on abandoned agriculture. But then he said, well, in what cases is the abandoned agriculture co-located with geological formations that are suitable for storing CO2 underground? And in this map, you can see the pink showing areas of abandoned agriculture and the gray showing areas where there's a decent possibility of accessing suitable underground basins and the intensity of the green showing how productive the areas are. And it's not too surprising that the areas that are marginal for agriculture are not the most productive. But if you say, well, what could we do on a marginal land? The conclusion is that you might come up with about 100 million hectares that are abandoned from agriculture and overlie a suitable geological formation. And that could result in around one to two billion tons of CO2 per year that could be injected into these formations. Again, it's a meaningful, it's a big business opportunity and a meaningful bite out of our emissions budget, but it's far from solving the whole thing. And the US is actually one of the, it's kind of the Saudi Arabia for Beck's potential. J. Beck led a really nice study that was published just a couple of years ago asking what is the overlap between areas that could produce biomass for energy use and areas where we have suitable underground formations for storage. And you can see the storage sites cross-hatch and the intensity of the green showing the amount of plant material available. The US has lots of good storage sites shown in the brighter orange colors and the plot on the right-hand side of the screen shows that the fraction of that capacity that has been used up already is very light and that there's real potential for increasing carbon storage. If you combine all of that, you get a picture of three regions in the US, kind of North Dakota, Montana, Illinois and the Midwest, and the Gulf Coast where there really is meaningful potential for substantial amounts of CO2 injection and available biomass that could lead in the near term to up to almost 100 million tons per year of CO2 injection. And within a few decades could lead to something in the range of about 300 to 600 million tons. Again, not solving the global problem but getting us pretty far along. As I leave the biomass energy topic, the one additional thing I want to talk about is wood pellets which are really new in the conversation. But you can see that the utilization of biomass for heat substantially greater than it is for transportation or electricity and that's mainly in wood pellets which are dominant part of the renewable energy strategy in the European Union, mainly because they're considered carbon neutral even though in many cases they're not. And pellets are attractive because they're a drop-in solution that doesn't require new technologies but they're a frustrating solution in that they create a tremendous pressure for deforestation in countries that are currently operating as carbon sinks. And I think that for an advanced wood pellet environment to move forward, it's going to need to address the fact that they're not really totally carbon neutral, that you might get modest emissions reductions from them. You know, spend a few minutes talking about natural climate solutions. And remember we're talking both about slowing emissions and about increasing sinks. It's been a really hot topic in the last couple of years because given generous assumptions, you can come up with some huge numbers about how much we might increase the carbon content of the land biosphere. Paper by Bastin and others was published in Science in 2019 argued that if you look at places that have protected areas and forest and then you look around the world and say, well, what other places have climates like that that there's almost a billion hectares, again, almost as much as we have in agriculture that could have trees and that that could store 750 billion tons of CO2 over some undetermined but presumably very long timeframe as whatever trees were planted grew. It turns out these estimates are incredibly optimistic given very generous assumptions, but they started a conversation about what would it look like if we planted a trillion trees? How much of the problem could be solved? And there's been interesting, useful analysis of that. Some of the most interesting has come from Bronson Griskeman colleagues who argued that if we are really ambitious, we might be able to deploy natural climate solutions as an important slice of a bigger mitigation pie. So if our mitigation is all this, we might be able to get natural climate solutions up to about 10 billion tons per year over a period of a dozen years or so, really resulting in making the climate problem transition from almost insolvable to one that we're really beginning to wrap our arms around. The analysis from Griskeman and others identified a whole bunch of places where improved management could result in either decreased emissions or increased uptake. Most of the potential is enforced and the largest potential is in reforestation. And Griskeman colleagues identified some of that as being available at very low cost, what they can call less than $10 a ton or a moderate cost up to $100 per ton. And you can see across the forest sector that the total sums to more than five billion tons if we're willing to have carbon prices up to about $100 a ton. One of the things that's challenging is we don't know very much about how we would actually deploy a lot of these strategies at scale, but we're beginning to see them deployed at meaningful enough scales that we're learning by doing and beginning to build up the stock of knowledge that's gonna be important in the long-term evolution of this set of technologies. I think the Griskeman potential is probably too optimistic and being constrained only by the finance, but it really sets an interesting, it sets an interesting dynamic. Other estimates have been similar to this ones from the National Academies in 2019 and it concludes that if you look across all the methods we might get up to on the order of five billion tons of CO2 per year, again, solving something like a quarter of the negative emissions that the IPCC in a quartile range says will be necessary. But what is the total capacity of the land and ocean sinks? Can we just keep pumping additional biomass into forests and grassland soils? Yeah, so my group has been working on that and you can think about ecosystems as working in two contrasting ways. One is that they're basically like a silo, a fixed capacity and that we cut down a lot of vegetation in the past and we can regrow that if we're good stewards of the landscape. The other conceptual model is ecosystems might act like a haystack where as a result of things like CO2 fertilization, you just add more and more and more biomass. If you think the silo model is correct, we're probably looking at a total storage potential in the terrestrial biosphere of something like a hundred gigatons of CO2 total. The haystack might allow you to get up to about 1,000. We know that over the historical period, we probably released between 750 and 1,000 billion tons of CO2 into the atmosphere as a result of cutting down forests and mistreating soils. We also know that that land sink that I talked about earlier has been operating over many years and has probably replaced about 500 billion tons. And so you might say, well, that the remaining that could be refilled with the silo estimate should be two to 300 billion tons. And if you look at calculations that people have done about the remaining potential in the biosphere, the average comes out at about that, maybe a little bit more optimistic. And there've been really a lot of studies published now that say, well, how much carbon could we get into the terrestrial biosphere? And they're all summarized here in comparison to that IPCC inter-cortile range. And there are a few that say we could solve the entire negative emissions problem with natural climate solutions, but many that are at much lower numbers. When we looked at all of this, we concluded that the most likely levels were gonna be in the range of about 200 billion tons and that with good management of the terrestrial biosphere and with attention to make sure that we stay at the lower range of the possible warming that we should be able to achieve something like this level and make a contribution to anywhere from 20% to maybe as much as half of the negative emissions that are required in the 21st century. Let me just close with two quick comments. The first concerns whether natural climate solutions are unambiguously good and then how much we should be investing in them. So it's important to recognize that natural climate solutions can be rich with co-benefits but they really produce some potentially serious challenges in the space of leakage. Does saving carbon someplace mean that it just gets cut someplace else? Permanence, does planting a forest now just mean it's gonna burn up in a hundred years? Or additionality, well, when you say you are preventing this forest from being destroyed or you're really doing something that you weren't doing otherwise. We also I would say just don't have the infrastructure together to provide high confidence in natural climate solutions. And when we invest in protecting ecosystems we ought to be careful to make sure that we recognize that most of the threats are coming in the area of finance, governance, and strong institutions rather than in understanding the carbon cycle. How much should we be investing? You know, many of the benefits that come from having a vibrant natural estate that aren't in terms of the carbon balance they're in terms of protecting biodiversity, protecting air and water quality, having an environment that meets people's intellectual emotional needs. And most estimates that we're probably spending something like 1% of our current climate portfolio on natural climate solutions. You know, there's no question that we ought to be spending much more than that but we also ought to be really attentive to the fact that there are there are real profound limits to how much we can get out of natural climate solutions. And even though it's tempting to rely on them for abundant solutions far in the future and we need to recognize there are profound limits and that the real pathway to effective decarbonization is going to be aggressive investments in decarbonizing energy and industry. At the same time, we make ambitious investments in taking advantage of natural climate solutions where they can help. And I think overall, you know, my philosophy is summed up in a piece we published in Science a couple of years ago. Natural climate solutions are wonderful but they're not enough to solve a problem. That's why I'd like to stop and I look forward to your questions. Great, thank you so much, Chris. As anticipated, there's very few people who could go into as much depth as you did in all the relevant areas and I claim no one who could weave the story together so artfully and really highlight a lot of the trade-offs involved is dispassionately and scientifically as you've done. Which leads to a lot of questions that probably only you can answer that kind of things I get asked all the time but don't feel qualified to weigh in on. The first one, let's just move for a little quick progression. That's food versus bioenergy. Where do you stand on that in general and what are the trade-offs and do's and don'ts in that space? So the idea is we have growing population. We might need, not sure we will need more land to grow more of these marginal lands to grow food in the years ahead. Do we run a risk if we use too much of it up now for biofuels? Yeah, so the most important key to understanding where we are in terms of the land we need for agriculture really has to do with future decisions about animal agriculture. I already mentioned that we use twice as much land for grazing as we use for growing crops. If you look at a crop like corn in the US we use about 40% for biomass energy but we use about 40% for feeding animals as well. And if we pull back on the amount of land and current crop production that we use for feeding animals we have abundant land that could be used either for biomass energy or for increasing food production. So that's, there's an important decision point that needs to be crossed and it's hard to say what direction we're gonna go with that. But nothing could play a bigger role in opening prospects for optionality in the future. A second thing that's gonna be really important is whether or not we can continue to increase crop yields at the one to 2% per year that we've seen over the last several decades globally. And if we can continue to do that then it may be that the amount of land we use for crops doesn't need to expand very much and may even be able to contract allowing us to use some of these lands for grown food. It's important to not think of the marginal lands as a right for use for biomass or food production because in most cases these were abandoned from food production because they weren't all that great. Great moving a little bit in that direction that we got a number of questions about what the boundary is of your natural storage. Well, actually natural and engineered. So I wonder if you could talk just a little bit about soil-based biomass storage including biochar perhaps and also ocean biofuel production. Just as things, do those give you optimism about large numbers being possible, small numbers don't do it under any conditions? I didn't talk at all about oceans obviously and there has been lots of speculation about way that we might use biomass in the oceans to increase carbon storage. It's important to recognize that on both the land and the ocean there's a strong connection between biological fixation and biological release and it takes very special circumstances for carbon to be stored for a long time especially in the oceans where the typical delay between fixation and primary production by a phytoplankton and release in the death of that organism or its consumption by another one is only a few days. So getting large amounts of storage is a much harder problem than just getting large amounts of photosynthesis. And there are ways to think about it, the sinking biomass that may turn out to be practical although my guess is that they'll be quite limited. You know, we have lost a substantial amount of carbon from global soils. Rebuilding carbon stocks in soils is something that can be done with good stewardship, can be done by increasing yields as well. And there are lots of win-wins in the biomass space, good stewardship of soils that can increase yields and increase carbon storage is one of the clearest win-wins. It's unlikely that the total amount of carbon stored is gonna be a significant fraction of, for example, this amount of negative emissions that are required in the rest of the century. Great. Then we have, not surprisingly, given our audience some very good probing questions on everything from the role of the private sector in promoting negative net emissions including natural and engineered sinks. And that maybe the private sector has many elements to it that things like green, is it greenwashing? Is it business opportunity in your view? Dominantly greenwashing, business opportunities, investment opportunities and whatnot. And alongside that, more generally, a lot of interest in equity defined pretty broadly we actually had several questions by a student from Iowa who said, who observed that in Iowa, there's a lot of biofuel production and nobody uses it, but they're cheap. In California, there's a lot of biofuel use but it's very expensive and by and large we don't produce any. So anything on that space that you would like to address further, particularly given how we can all work together in a kind of fair and just future which seems to be the ethos of the current administration. Yeah, it's a really great question and I'm really glad that people asked it. The balance sheet of how much we can accomplish with biomass energy and natural climate solutions could, it could be a large number or a small number with lots of private sector participation with lots of commitment to emphasis on equity and empowerment of poor people or not, they could evolve independently. I think let's first look at the opportunities for the private sector and we have relatively immature markets for natural climate solutions especially and many of the arguments in favor of natural climate solutions are that they provide compelling life opportunities for indigenous communities and for developing economies and they certainly do but at this point the incentives are far from in place in order to bring those to maturity. There's also the risk, especially if you think more in terms of commercial biomass production that some of the areas most important for indigenous communities might be converted to large scale plantations which can generate large amounts of carbon but are really hard to manage in an equity fulfilling mode. There has been in the natural climate solutions community especially an appropriate and important focus on advancing equity agenda in parallel with the natural climate solutions agenda and that will require a lot of work in the biomass energy space. I think we're likely to see the same kinds of trends that we've seen in other manufacturing and services and unless there's a real commitment to making sure that equity considerations are paramount. I know for example you're supporting some work on market design in a way that's designed maybe you need NGO and international community support for this to make these offset schemes a good deal for these small holders so-called in developing countries and not allow them to be used for the benefit paid for but also for the benefit of people outside sometimes to the detriment of the so-called small holders. Do you think we need more research in that area and more thought about how to organize that and create the proper incentives for both sides of the equation? Absolutely, you know offset schemes where an emitter can purchase offsets in order to continuing emitting but still meet a decreasing cap have been incredibly unpopular in the environmental justice community for people who live near emitting facilities the idea that the facility can continue emitting by protecting the forest thousands of miles away is grotesquely unfair and I totally agree with that. And so one of the things that we need to do is distinguish offsets that are essentially wheezing out a responsibility from developing new ways to remove carbon from the environment from the atmosphere or to decrease emissions. And I think that the design won't come out in a way that works for people in communities and economies unless that's a really intentional goal. And I would say that we are just beginning to have the kinds of conversations about how to make that a reality. Super, more generally a closing question in your transition to the post event press conference with selected students. What advice would you give to students who wanna join this quest for decarbonization from your point of view? Everything from how can they get a job in your lab or get into your grad program to have a career that lasts many years or be impactful. Any tips on where you think the most help is needed and therefore that would be most fulfilling for the students in the audience? I'm always eager to talk with people who wanna do research in this area so they should definitely contact me. But I am seeing a real explosion of interest in private sector ventures in this space either focusing on carbon quantification using especially satellites and advanced eddy flux and lots of technologies for having a better sense of how carbon stocks are changing over meaningful landscapes, whole countries in many cases. There's lots of work in actually setting up the financial markets. And we're seeing lots and lots of work in the actual production and processing of especially biomass energy. So I think that the stage we're at in general is that even though a few aspects of this space are technologically mature, it's really only beginning to spin up as a core part of a broader climate solutions agenda. And my expectation is that it's gonna be a big employer in coming decades in the finance space and the technology space in the environmental monitoring space and hopefully in the environmental justice space as well. Great, thank you so much, Chris. Before I give you final thanks, I'd like to alert the normal attendees of the seminar that there's no seminar next week in respect for the national holiday. I think it's president's day next Monday, so no seminar next week. With that, I'd like to thank Chris one last time for a very engaging, thoughtful and important seminar on a subject of great importance. Thank you so much, Chris, for all you do and for this great talk today. And now you can transition to the student portion of the talk for those lucky students. I think I'm unable to bid my way into the post seminar. So thanks once again for a great talk and we'll look forward to seeing more from you every day in the next four years and hopefully more. Thanks. Thank you, John. Thanks, everyone. Thanks so much.