 I would like to welcome Professor Chris Field for our next session. Professor Field is a director of the Woods Institute for the Environment. He is also professor of earth system science and biology and also a senior fellow at the Precord Institute for Energy. Professor Field's research has focused on climate change and he's been deeply involved with national and international efforts to advance the understanding of global ecology and climate change. Truly a world expert. He was the co-chair of the working group too of the IPCC from 2008 to 2015 and I'm so happy that he was able to join us today. Chris, looking forward to chatting with you, hearing from you. So yeah, whenever you're ready, the floor is yours. Thank you and welcome everybody. I want to add my voice in a really warm welcome to Stanford, whether or not you're here physically. What I'd like to do this morning is share a few perspectives on climate change and how climate change sets the stage for what we need to accomplish in terms of an energy transition and more broadly a greenhouse gas transition. In order to do that I want to repeat some of the same things that Arun's already spoken to you about that set the time scale of the response and I want to explain a little more background behind why it is that there's a fixed carbon budget and whatever else we do we need to respect the fact that the biogeochemistry and biophysics of the earth system keep this budget fixed and in particular what I'd like to do is really focus on the concept that regardless of where we are with the technologies, regardless of where we are with the policies, but avoiding the worst impacts of climate change is basically about finding the accelerator pedal. You can talk about it as the inflection point in energy, you can talk about it as enabling new technologies but across the full spectrum of responses what we really need to do is find a way to go from pace number one that we're at now to pace approximately 10. Let me start with a picture of the global average temperatures for land and oceans over the last 140 years or so. It's essentially no question that it's warming if you quote from the most recent reports of the Intergovernmental Panel on IPCC the conclusion is that warming is unequivocal and it's extremely likely that humans are the dominant cause of warming since the middle of the 20th century or so. And you know you could ask does that mean that there's still a sliver of doubt? The basic answer is that there is a sliver of doubt of whether humans are the overwhelmingly dominant cause or the slightly dominant cause. Most of the evidence are that in the absence of human emissions of greenhouse gases we'd be see looking at a slight cooling over the last century so that humans have caused all of the warming we've seen and a bit more. There's tons of evidence of why this is the case. What I'd like to do is make just a couple of comments that establish how settled the science is on the link between greenhouse gases and warming. This obviously is the first page of a kind of a beat-up scientific article published in April of 1896 nearly 125 years ago by a Swedish chemist named Arrhenius and in 1896 three fundamentally important parts of the relationship between greenhouse gases and climate were already well established and they've been challenged tens of thousands of times since 1896 but none has really been found wanting in terms of the underlying physics or in terms of the empirical evidence. The three things that Arrhenius knew in 1896 are that carbon dioxide is a strong absorber of heat radiation that's released from the earth's surface. The second thing that Arrhenius knew not really found wanting in any way since then is that you know warmer atmosphere there'll be more water vapor which is another strong heat absorber and that water vapor feedback essentially amplifies the effects of the carbon dioxide and the third thing that Arrhenius knew was that if you release a bunch of carbon dioxide to the atmosphere over decades and centuries it will partition between the atmosphere and the oceans and you can calculate what that equilibrium will be based on these three things greenhouse gas water vapor amplification and an atmosphere ocean partitioning Arrhenius was able to calculate an expected effect on global temperature of a doubling of carbon dioxide concentration in 1896 and although he didn't get exactly the answer that we get today it was pretty close so the core elements of the physics behind our understanding of the way greenhouse gases change climate have really been in place for more than a hundred years and they are as established as for example the physics of the way an electric motor works or a fluorescent light bulb. There's essentially no question and when we look at scientific controversies related to climate change they're all about whether there are feedback mechanisms that lead to amplifications or suppressions whether there are links between particular aspects of the climate system and other aspects how things play out on a on a spatial or a temporal basis but the core elements of the scientific understanding of climate change have really been in place for at least a century and and even more. Much of the issue and the real reason that we're talking about climate change in the context of the energy system is that our energy system over the past century has been focused on combustion of fossil fuels that lead to an increase in atmospheric CO2 concentration. Last year was in some ways a frustrating landmark year and the concentration of carbon dioxide in the atmosphere was the the first year that we've seen year-round concentrations that were greater than 400 parts per million point zero four percent but it's also important to recognize that carbon dioxide isn't the only greenhouse gas of concern and currently if we look at the amount of forcing of climate about two-thirds of the forcing comes from carbon dioxide and the other third comes from a mixture of of methane. Haroon already talked about nitrous oxide which comes primarily from agricultural practices and halocarbons these refrigerants that Haroon talked about. But there are some special reasons that CO2 is important and i want to explain those before we get too deeply into the material and the core issue that you need to understand is that CO2 is is uniquely important as greenhouse gas because warming from CO2 is at least to a first approximation permanent. Here's a trajectory of CO2 emissions if you look over the last 30 years you can see that the emissions trajectory really hasn't been stable. You could see that there was an emissions downturn with the with the great recession of 2008 2009 you can see that emissions were basically flat around the time that the Paris Agreement was signed 2015 2016. They've been growing since then it's likely that the pandemic will cause a decrease in emissions and in some ways the frustrating news from the decrease that we're seeing during the pandemic is really solid evidence of how tightly linked economic activity and greenhouse gas emissions CO2 emissions are at this point still and of course the the goal of the energy transition is to shift the energy system from this tight linkage between CO2 emissions and energy production to one that's totally unlinked so that we can have abundant affordable energy and the absence of greenhouse gas emissions. If we look regionally at where emissions are coming from it's important to recognize that that the nature of the problem is really fundamentally different than we thought it was back it's interesting to go back on this figure to something like 1997 when we signed the Kyoto Protocol and at that point the understanding of the way the world works is that if the world's developed economies especially in the in the US and the European Union could cut their emissions we didn't really need to worry about emissions from the developing world for some years or decades into the future and of course that situation changed dramatically with massive acceleration in emissions with economic growth in China beginning around 2000 so that now annual emissions from China are about the same as from the US and the EU combined and we think about solving the problem we really need to think about a global scale solution where wherever solutions are developed they need to be deployed and affordable around the world and we do think really really hard about assurance that whatever solutions we come up with are global ones. When we look at the sources of the emissions in terms of what compounds it's still the case that emissions from coal are the leading source of industrial carbon dioxide followed by oil and gas cement and then flaring and we talk a lot about the the rapid increase in gas and the US now gas is is more important than coal but but globally coal is still the number one source and it's amazing that we're still relying so heavily on a technology that not only leads to so many greenhouse gas emissions but has so many other negative health consequences with with hundreds of thousands or even millions of people dying every year as a result of particles from coal. Part of the reason this is such a hard problem as Arun already explained is that greenhouse gas emissions are associated with a super wide range of activities almost everything we do in the economy in the roughest of terms you can think about greenhouse gas emissions being associated almost equal proportions to to transportation industry buildings and food production it's really striking when we think about for example on the Stanford campus pressure from student groups especially to divest from oil and gas that transportation least globally is a relatively small slice of the total emissions budget and the big ones industry buildings agriculture forestry and land use are really complicated to deal with but at the same time they're complicated they have a number of really attractive opportunities for saving money at the same time that greenhouse gas emissions go down a final source of emissions that i want to make sure people don't forget is emissions from land use when we go back to the half a century or so to the 1960s emissions from land use change were comparable to emissions from fossil fuel combustion but they have stayed more or less steady over the last 60 years while emissions from fossil fuels have have increased dramatically so that now in in recent years the emissions from land use change in in recent years this is almost entirely the clearing of tropical forests have been between 10 and 15 percent of the magnitude of the emissions from from fossil carbon when we think about bringing emissions down to zero we're going to have to tackle land use change as aggressively as we task tackle fossil carbon and spend a few minutes talking about the the relationship between the cumulative emissions of carbon dioxide since the beginning of the industrial revolution and where we stabilize temperature this figure shows the relationship between cumulative anthropogenic CO2 emissions beginning in 1870 and the stabilization temperature and what you can see is there's essentially a linear relationship at reading the the numbers across the the top line if we've if we have emitted on the order of 2,000 billion tons of CO2 we're looking at a temperatures of around one C at 3,000 billion tons of CO2 we're at about three C so this cumulative emissions were really really important and it doesn't matter when they're emitted and it doesn't matter whether you know we slow emissions or whether we speed them up the the relationship is with the cumulative amount and the reason for that is that warming from CO2 is essentially permanent there's a simulation that illustrates why that's the case and this is a model simulation in which a huge pulse of carbon dioxide either 2,000 billion tons 500 billion tons or 200 billion tons is emitted to the atmosphere as a pulse and then you can follow the atmospheric CO2 concentration in the top figure or you can follow the global average temperature in the in the bottom figure and what you can see is that as Arrhenius Neubach in 1896 the CO2 concentration gradually goes down as the carbon dioxide partitions between the atmosphere and the ocean but but the temperature is essentially constant and this is over a period of 500 years why is that the reason that's the case is that the vast majority of the warming that's associated with atmospheric CO2 is ending up in the oceans and as the as the CO2 gradually partitions between the atmosphere and oceans the ability of the oceans to take up heat is basically slowing down at the same rate that the CO2 uptake is slowing down and what that means is that even as the CO2 is decreasing the fraction of the heat that's remaining the atmosphere is increasing and it means that you have this essentially permanent warming in and as far as we can tell the warming from CO2 is is permanent over many centuries probably many thousands of years unless we actively remove the carbon dioxide from the atmosphere with non-natural processes and and one of the things that we'll talk about and is a subject of a lot of work at Sanford is how it is possible or what will it take in order to remove large quantities of carbon dioxide from the atmosphere so let me just go through the implications of this now for the budget Arrhen did a rough budget for a warming of 2C and I want to go through the the same calculation for 1.5 just to really put an exclamation point around how much time is available so the best estimate is that if we're going to have a 66 percent or better chance of keeping global average temperature below 1.5 above pre-industrial it's currently around 1C above pre-industrial that budget is on the order of 2,800 billion tons of CO2 and through 2019 the best estimate is that we emitted a little bit over 2,300 billion tons you guys are good at addition that means we have 485 billion tons left in order to keep ourselves within this 66 probability of staying at 1.5 C or less and you can just ask how much time that would be at current emissions in 2019 the emissions rate was around 43 billion tons for the entire year and if you divide 43 into 485 you come up with 11 years and four months April 2031 is the date at which we're essentially committed to a warming of at least 1.5 C a room did the calculation for 2C and the the same kinds of considerations apply at least for me the implication of this calculation is that whatever else happened we need to find a way to find the accelerator pedal on solutions and what i'd like to do now is is put this need for an accelerator in the context of the impact that we expect from from a changing climate so here's a here's a typical emissions trajectory that that subject of wide discussion throughout the economy this is one of shells and what you can see is that it has emissions peak and then decline and then a large amount of negative emissions later in the century so that we go to net zero emissions somewhere in the in the second half of the century that that's that's very late relative to the requirements of the staying in the 1.5 C and from the IPCC you can see a a wide range of of possible emissions pathways that are associated with stabilizing temperature anywhere from only a little bit over one to allowing it to go all the way up to more than more than four and a characteristic of of all these scenarios that limit warming in the range of one and a half to two C is that they typically bring global emissions down to zero somewhere in about the middle of the second half of this century and then emissions are net negative in the the latter decades of the century so that we are on bulk removing more CO2 from the atmosphere than we're adding why is it we need to do that I'm just a couple of minutes talking about the impacts of climate change and I think everybody's aware that we're already seeing impacts of climate change and that if this is stated in the goal of the UN framework convention that the goal is to avoid dangerous anthropogenic interference with the climate system we've already failed but the the impacts are still at the stage where they're mostly manageable and what we need to do in the long-term future is avoid the kinds of tipping points where those impacts become unmanageable so we've seen impacts and we've seen them everywhere I'll highlight just a couple of the things that have been in the news recently we know that climate change is a big factor in the risk of the kinds of droughts that California saw in the 2011 to 2016 timeframe we know with a very high level of confidence that climate change contributes to the risk of the wildfires where we're still experiencing the smoke today and we know that climate change not only as a result of higher sea levels but as a result of warmer water temperatures increases the probability that hurricanes reach the most destructive categories and we know that it increases the the amount of rainfall that's associated with any given hurricane we look into the future I would argue that the that the most important thing is to find a way to keep the impacts manageable and if you look at every assessment of the impacts that we're looking at the common theme from all of those is that increasing warming increases the probability of impacts that are severe and pervasive and irreversible what's that mean in terms of of the outcomes the the two global maps in this figure show a world with ambitious mitigation the world with the average temperature shown in the in the blue banner across the top and the and the right hand figure shows a world of continued high emissions I want to point out two important things about these two contrasting worlds the first is that if we think about the next few decades the the decades over the black arrow in the top we're looking at a time when the temperature trajectories from the pathway for the world of ambitious mitigation and the world of continued high emissions don't really diverge this is a world where we have to take responsibility for the changes that have already been baked in and where adaptation is going to be the key to dealing with the problems and it's really only in the second half of the century we might think of as the era of climate options when investments that we make in the next few years play a big role in terms of of the climate outcomes in the in the second half of the century and the second point I want to make is illustrated by the contrast between the the top map the map of the amount of warming that occurred over the past century with the amount that we can expect in the decades remaining decades of the 21st century and what you can see is that in a world of ambitious mitigation in this world we will see about as much warming in the rest of the century as we've seen to date an amount of warming that's definitely causing damages but in general we can deal with and if you contrast that with the world of continued high emissions it's really a world that is so different than current conditions very very difficult to even project what the impacts might look like I want to close with a description of three kinds of impacts that are potentially important tipping points and that really at least for me highlight the reasons that we need to be so focused on this accelerator pedal the first concerns the risks of very large amounts of sea level rise the understanding of the risk of collapse of a major ice sheet is definitely a work in progress but there's increasingly clear evidence that as we move from low emissions through the century to higher emissions the the risk of large amounts of sea level rise up to a couple of meters is really really clear but if we look in the long term the picture changes dramatically so that in a world of continued high emissions through the 21st century we're looking at the probability of something like 15 meters about 50 feet of sea level rise that persists over many hundreds of years fundamentally changing the world's coastlines where in a world of ambitious mitigation sea level rise is certainly consequential but it's at a level that could be managed with the kinds of adaptation strategies that we already have access to we're really really clear that there's a tipping point that's associated with a very large amount of sea level rise out there somewhere it's unlikely that that tipping point is at a global warming less than 2c and it's unlikely that it's at a global warming greater than 3c exactly where it is is hard to pin down you'd say the same exact thing for a tipping point that's associated with release of large amounts of carbon from thawing permafrost we know that there's a vast amount of carbon frozen in these soils especially in Siberia we know that it's very susceptible to thawing and we know that we have not yet seen the release of large amounts of carbon from the thawing of these permafrost soils if you look at the quantities they're they're they're truly vast here's an indication of the remaining forever budget for the 66 chance of staying below 1.5 and what you can see is that the release of carbon from thawing permafrost could by itself overwhelm that budget again we don't know where the tipping point is but we have high confidence that exists the final tipping point I want to mention is one that deals with the ability of society to work together to solve these problems and this is a figure from Marshall Burke at Stanford and basically what it shows is that if you look at the economic consequences of historical variations in temperature what you can see is that countries that are currently cool do a little bit better when temperatures are warmer countries that are currently hot do a lot worse when temperatures are warmer and if you simply project that into the future you end up with the globe where the rich countries and the global north are doing dramatically better and the poor countries in the global south are doing dramatically worse and at least to me what this figure speaks to is a tipping point in the global social license to tackle climate change and it really will need to be tackled at the global scale and I think passing this tipping point means that we lose the ability to deliver the solutions that the world's demanding this the session of this week is going to talk about a whole bunch of important aspects of the solution and you know technology is certainly one but it's not the only one we also need to be understanding where there are opportunities in finance where there are opportunities in policy and where there are opportunities in adaptation and finally a thought I want to leave all of you with is that more than anything else and getting ahead of climate change is having a priority that establishes what I want to call leadership the ability to recognize the problem to make the in kinds of investments and to inspire the community to deliver the solutions that the world needs thanks very much I'd love to have any questions hi yes professor can you hear me I can need for the super insightful talk I just had a quick question about how you mentioned that there is this huge discrepancy where the global north is generally going to be a lot better off than the global south in case of a drastic change in temperature what do you think would then provide the global north the incentive to work on climate change solutions given that the global south doesn't really have the resources or the technical know-how to actually build and implement these solutions are we you know going to leave it to the goodwill of people generally north america and europe for example or is there a framework that you have in mind to address that you know there are there are two schools of thought on how to globalize the solutions one school of thought is that if the prices of the technology can be driven low enough so that the non emitting solutions are the obvious choice that those will be adopted based on the economic criteria alone in the global south and I think there's a lot to be said for that argument the other is that if we really want to find the accelerator in the appropriate way that we really need to think about international assistance and in a different way than we've been thinking about it and and my analysis is that waiting for the prices to come down makes things happen way too slowly and that actual subsidies are going to be really critical for allowing countries that don't currently have the resources to make the investments that get them on the track that's going to allow the global emissions to stay somewhere close to the total budgets available hi thank you for your talk I was very curious about what work is being done on changing public perception and behavior relating to climate change and kind of how to get more people on board with doing work that that will help reduce the climate change yeah that's a great question and it's really clear that it's not just a technology problem it's also not just a communications problem and I would say that what we lack is an ability to conceptualize understand and move forward with the integrated system that recognizes all the pieces at sanford we have a bunch of people who are working on climate communication there was just an article in the New York Times the other day about a new poll on perceptions of climate change and the number of people who view climate as a top priority at sanford's there's active efforts on climate change communications in the communication department in the school of education in the psychology department but it's an area where we we really need a lot more work and where we need a lot tighter integration between that community and the people who work on the technology and the finance of the government