 Hi, everybody. Welcome to Stanford. And as Arun said, I lead the Institute for the Environment on campus. And it's a wonderful partnership with the Institute for Energy recognizing that there's kind of this inseparable link between where we are with the environment, where we are with climate, figuring out how to solve the climate challenge, and how we deploy energy to meet people's legitimate needs, at the same time we don't do irreparable damage to the environment. I've been really impressed at the questions that folks have asked so far. They've really hit all the key issues that we need to understand. How do we move forward in an environment where there's still, I don't want to say uncertainty, there's still skepticism about whether climate is a problem that warrants the level of focus that is going to be required. How do we deal with the negative externalities of new technologies, and particularly how do we deal with the social and equity issues that come up whenever there's a massive transformation. Another really important component that we need to keep on the radar screen is that there's some fundamental mismatches in the trajectories of the change that we're only beginning to grapple with. Arun showed you the IAEA estimates of the fraction of coal remaining in the economies of China and India by mid-century, and they were like half of the energy still coming from coal in those countries at the middle of the century, when we've already characterized a lifetime carbon budget that requires us to be at essentially zero emissions at the same time if we want to be anywhere close to the 2C target in the Paris agreement. So what I want to do is basically step back through what we know about the climate challenge, where the uncertainties are, how to think about the way that impacts scale as we move from lower amounts of warming to larger amounts of warming in the system, and kind of set the stage for the way to think about impacts and the consequences of stabilizing at one level or another. Normally in this kind of presentation I would talk substantial about where the emissions are coming from and the kinds of levers we might have in terms of finance and technology and policy to address those emissions, but following me Rob Jackson, who's a real expert in the emissions landscape is going to speak to that. The photo I have here is Stanford's first large-scale PV array. This one's in Kern County. It's a 50 megawatt array that provides about a third of the campus energy and the next big PV array is just about to go online, and it'll mean that Stanford is getting 100% of its electricity from these renewable sources. It's an interesting and complicated confirmation of the rate of change. I think the power purchase agreement price on this array is a little over two and a half cents a kilowatt hour, with the new one in Fresno County it's going to be a little under two cents a kilowatt hour. So it's essentially providing electricity at half the price of fossil, but that's California and in most of the world what we're seeing is that emissions from fossil are still going up. So what I want to do is is really dig in to where we are with understanding the climate challenge and what we can do about it. It's the plot of global mean land and air temperatures over the last 140 years or so, showing really profound warming. As Arun said, it's about 1C now over the 20th century average, about 1.2C over the pre-industrial level, very rapid warming in the last few years. One of the things that's really striking about this is that pretty much every one of those big spikes in temperature has been in an El Nino year. During El Nino years the ocean is less good at taking up heat and it really illustrates the way that the pattern of warming is kind of a dance between the external forcing that's being imposed by the additional greenhouse gases in the atmosphere and the internal processes that regulate the earth system. I'm not positive I'm going to be able to show the next simulation but what I'd like to do is show you the the spatial pattern really highlights the importance and I think in order to do that I need to apologies for one second here I just need to present or unfortunately okay well that really helped me a lot. I'm gonna forget that okay I'm not gonna show you the the spatial pattern but what's what's really important to understand is that the spatial pattern is really driven by this strong gradient from the equator to the poles with the most profound warming by far occurring at high latitudes. A lot of the reason there's been so much concern about Greenland and the Antarctic Peninsula in recent months because the warming there is really two to three times what it is in the rest of the world. I want to step back and take you through the trajectory of how long we've understood the basics of the climate challenge. This is the cover sheet of a of a really good paper I recommend reading. This paper by Svante Arrhenius, brilliant Swedish chemist, was published in 1896 and the title is on the inflows of carbonic acid in the air upon the temperature of the ground. 1896 so more than 120 years ago Arrhenius knew three important things. He basically knew all the things we need to know to know that emissions of carbon dioxide to the atmosphere will warm the earth. He knew that carbon dioxide is a absorber of infrared radiation. It's a strong absorber of radiation the wavelengths that objects the temperature of the atmosphere surface. He knew that a warmer climate would create an atmosphere that held more water vapor and he knew that water vapor is also a greenhouse gas that absorbs infrared radiation and that this extra water vapor in the atmosphere would amplify the effects of the carbon dioxide. The third thing that Arrhenius knew in 1896 is that in the long run any CO2 that was emitted to the atmosphere would eventually partition between the atmosphere and the oceans with about 80% of it ending up in the oceans. So with those three things understanding the IR absorption of CO2 the water vapor amplifier and this partitioning of carbon dioxide between the oceans in the atmosphere in 1896 Arrhenius was able to calculate how much warming you would expect from a doubling of atmospheric CO2. Didn't get it exactly right. He was about one and a half times greater warming than we expect now but all the pieces of the physics were there. All the foundations of the understanding and in 120 years people have been challenging this again and again and again in tens of thousands of publications and nobody has found a fundamental flaw. All the climate science research since 1896 has basically been looking at nuances at things like the spatial patterns at factors that amplify the response a little bit in some places and suppress it in others and that fine-tune our understanding of what levels in the atmosphere the different processes are occurring. And you know when we think about the level of confidence we have in in this process the forcing of climate change by the emission of greenhouse gases from human activity we really understand this process at a level of completeness that's you know for example the level of completeness we understand how an LED light bulb works or an electric motor. This is fundamental understanding that has been reinforced through thousands of papers over many decades. The idea that there's something controversial about the role of humans in causing climate change was really eliminated decades ago and the idea that there's core uncertainty about whether humans cause climate change is really a process of a political dynamic and not of a scientific one. You already saw the plot of the CO2 profile and CO2 has been measured with high accuracy since the mid 1950s and Montelot Observatory in Hawaii and many other locations around the world. This is the plot from last month where the number was just over 410 parts per million rising from about 315 parts per million in 1957. We know that over the last 800,000 years atmospheric CO2 has typically been around 275 parts per million in interglacials and about 185 parts per million in glacial. So we've seen about a 40% increase in atmospheric CO2 and the consequences of that are that the atmosphere is trapping extra heat and that heat's being distributed between the atmosphere and the ocean and we're seeing it in global temperatures. I guess I'm not going to be able to show the the spatial and and seasonal pattern of the of the CO2 and the temperature because of the of the computer but I recommend you look at these these Ed Hawkins simulations at some point. They show a wonderful spiral of the seasonal and inter-annual pattern of CO2 concentration and temperature and what they really highlight is the way that emissions have accelerated and warming has accelerated especially since the late decades of the of the 20th century. We also know with a very high level of confidence what processes are responsible for the warming. Unfortunately I'm not going to be able to to show this simulation either but it was done by by Eric Rostin in in business week and it and it really very beautifully shows if we look year by year from the end of the 19th century at the actual pattern of temperature and we look at the potential contribution of that from solar forcing from volcanoes from land use change from aerosols and from greenhouse gases what we see is overwhelming evidence that it's the greenhouse gases that are the dominant factors natural factors all together expected to cause a modest cooling of the climate and we really have a detailed understanding of the physics of the way that each of the possible factors interacts with the atmosphere and can disentangle them in a way that's that is about as settled as this kind of issue can be you know there's still uncertainty there's still important questions to address in the dynamics of the way the climate system works but those are those are questions of nuance and questions of detail not of the fundamentals. Here's the overall pattern of where we are in terms of the total forcing of climate change since the middle of the 18th century and as Arun has already pointed out there are important forcings of climate that are coming from carbon dioxide but from other compounds as well so about two-thirds of the forcing is coming from carbon dioxide and of the well-mixed greenhouse gases the other three important classes are methane nitrous oxide and halocarbons. Methane has three important sources it comes from methane production as Arun has already characterized it also comes from agriculture and from natural wetlands. Methane emissions have been going up rapidly recently with increased sources coming from all three of those from the natural gas production agriculture and wetlands a real challenge to manage especially on the agriculture side where the set of technologies is much less mature than the technologies for reducing CO2 emissions Nitrous oxide is an especially challenging greenhouse gas about 300 times as powerful as CO2 on a on a weight basis lasts in the atmosphere for a long time the atmospheric half-life is about 300 years and it's a result mainly of the way we do agriculture especially in animal production manure management and fertilizer treatments a real challenge and then the third important set of well-mixed greenhouse gases is is halocarbons refrigerants and these are compounds that are also very very powerful in terms of their greenhouse gas forcing some of which last in the atmosphere for a long time some of the changes that we made in response to the Montreal protocol to decrease destruction of stratospheric ozone ended up with compounds that actually were worse for climate and the new Kigali amendments are intended to address that some of the clear successes are in managing these halocarbons but there's still real challenges ahead as you know we have been losing ozone in the stratosphere as a result of the the halocarbons and and as a consequence there's less warming from stratospheric ozone than there would have been if we hadn't been destroying the ozone but there's more warming from tropospheric ozone because we're producing ozone in the troposphere as a consequence of other pollutants that we're releasing near the near the ground. One of the most important things that's happening in the climate is that we're not seeing the consequences of all of the greenhouse gas forcing from the well-mixed greenhouse gases because aerosols which are also a result of industrial activity are in most cases producing a negative effect a negative radiative forcing they're tending to cool the climate so the net result the total anthropogenic forcing we're seeing is a little more than two watts per square meter about one percent of the total energy reaching the earth surface and in rough terms the total anthropogenic forcing is now about the same as the CO2 forcing with these aerosol impacts more or less offsetting the effects of the other well-mixed greenhouse gases. Somehow we never seem to be able to escape from the narrative that maybe changes in solar radiation are having some kind of an effect on the long-term trajectory of global temperatures but you can see here that the solar irradiance effect is is truly tiny taken over time and if you try and ask about other kinds of mechanisms that might be related to solar irradiance and there's been a popular theme in the climate skeptic community about a possible role of of galactic cosmic radiation there's simply no evidence that takes it out of this this size range of of being totally a trivial driver. We have had important effects of land use change on climate and basically the the deal that's happened with land use change is that humans have cut down forests in many parts of the world and in general the landscape that's left after the forest is cut down is slightly more reflective than the landscape that was there when the forest was there and that's resulted in a in a small net cooling of the consequence of land use change. One of the really interesting themes in ongoing research is if we want to use natural climate solutions better stewardship of ecosystems to address climate change are we better off growing new forests where there weren't forests protecting forests where we've got forests now or allowing deforestation to continue and one of the really challenging patterns is that there's some places where growing forests actually makes the climate warmer even though the forests are taking carbon from the atmosphere they're also making the surface darker and absorbing more of the radiation. Okay, a really really important constraint on the way we think about solving the climate problem is that warming from carbon dioxide is essentially permanent. We know that warming from CO2 lasts for at least 10,000 years unless we actively remove the CO2 from the environment. What that means is that we've got a forever budget for whatever temperature Arun showed you the budget for 2c this is the budget for having a 66 probability of keeping warming below 1.5 c and the budget's around 2,800 billion tons of CO2 forever from the start of when we emitted till the time we stopped and the amount that we've emitted so far is a little over 2,200 you guys can do the math that means that the remainder is for a 66 chance of being below 1.5 around 570 Arun said it was around 800 for two and the emissions rate is around 40 and if emissions are to continue at that rate that means that we've got 13 years seven months until we're essentially committed to 1.5 we have a few more years if it's two but the real challenge is how do we go from that understanding to e-carbonizing on a timetable that's consistent with it and the bottom line is that you guys are going to have to figure out the answer we have a lot of technologies we have a lot of understanding but we also have a lot of constraints and I hope this week is going to be um um compelling introduction yeah do you have a question you know that's the uh 20 trillion dollar question we we we have known uh for a long time that climate was changing in fact I mean one of the things that's um well I I guess it's frustrating is if you read the arenas paper he actually concludes by saying and uh you know it's really kind of cold and miserable in the UK and in northern Europe and maybe we'd be better off if it was a little bit warmer and um and and and that theme of argument has been slow to disappear but I think that it it's really only been in the last few years that there's been a truly broad appreciation that climate challenge is is associated with impacts that are really going to be a unacceptable constraint on people's legitimate aspirations for a better life and the first report on climate change risk to the United States was in 1965 uh the first major report from the National Academies of Sciences was in 1979 the first report from the Intergovernmental Panel was in 1990 and so why is it that the transformation from core scientific understanding to really global mobilization has extended over so many decades and you know I think there's some there's some psychological reasons that it's difficult to accept the idea that things need to change I'm sure there's been some dedicated misinformation from various actors on the stage who have a vested interest in seeing things not change and uh the genuine technology issues that haven't yet been solved and I think a lot of the motivation for having a session like this is that if there's one thing that's clear it's that we need to work on all those we need to work on the psychological aspects we need to work on the the messaging and the disinformation and we need to work on the full set of enabling technologies whether they're in the finance or the or the technology or the or the adaptation uh huh yeah sorry thanks um some tipping point takes place and then some some um accelerating cycle kicks in but if I look at the scale that you have on there it almost shows that every hundred gigaton added it leads to the same amount of temperature change so it almost negates it's almost linear yeah it's almost yeah so is that is that fair to say that from from the science itself it is almost linear and and and there is no such a thing as a tipping point no uh the first thing you said is correct the the response of temperature to emissions is essentially linear but the impacts to temperature is not linear and that's actually what I was going to talk about next um the there there are three kinds of tipping points that I think we should be focused on one is a tipping point in whether the warming is self-sustaining or not whether we see releases of greenhouse gases from the earth system that that sustain the warming independent of whether there is further emissions the second kind is is tipping points in terms of impacts where um and seal rises the best example we pass a threshold where we become committed to very large amounts of seal of arise whether or not the warming continues and then a third I I think is tipping points in terms of the ability of society to keep cohesive enough that it can really realistically tackle the problems and I'll speak to each of those okay um let me let me just start out by saying I think the fundamental question isn't whether or not we can stabilize it 1.5 or or two but it's really whether or not we live in a world of ambitious mitigation where we stabilize somewhere at the low end of the range or a world of continued high emissions and in IPCC speak um radiative forcing of 2.6 watts per meter squared is ambitious mitigation uh continued high emissions is is radiative forcing at the end of the century of something like eight and a half watts per meter squared and you can see the contrast in temperatures where with um a world of ambitious mitigation we we see additional warming sort of on the scale of the warming that we've already seen in the last century we can imagine this world and we can imagine a set of steps that can allow us to adapt in a in a thoughtful way to it even though there be fundamental changes and and deep challenges that need to be addressed this world of continued high emissions is one where when we talk about impacts we're really so far outside the range of experience that it's hard to say anything particularly meaningful and it's a world that is a nightmare in in many respects not the least of which is that in the world of continued high emissions you can see it in the in the orange plume on the upper part of the scale we are at the end of the century not only something like four and a half sea warmer than pre-industrial but we're warming at about two tenths of a degree sea per decade and that continued warming is is perhaps the the most concerning aspect also want to identify two parts of the time sequence you can look at the global average temperature trend and the contrast between the world of ambitious mitigation in the blue and continued high emissions in the orange and what you see is that there's a period of the next few decades where they really don't diverge significantly it's a consequence of the inertia that's built into the global energy system there's simply no way that we turn off emissions tomorrow and there's no way that we turn off the geophysical processes that are driving global temperatures so you can kind of think about this as an era of climate commitment you know we we are going to see increasing impacts we need to deal with those impacts through adaptation but then especially after about the middle of the century we're in an era of climate responsibility where choices we make today and choices we should have made a decade ago really drive profound differences in the outcomes and a lot of what we need to think about is how we want to deal with this era of climate commitment where we need to make investments in adaptation at the same time we make appropriate investments in the era of climate responsibility okay so let me just highlight that we have in the last 20 years or so profoundly moved out of the era where we think about climate change as something that's a likely future impact that's going to affect someplace else in the world now we've seen climate change impacts that are widespread consequential we've seen impacts on every continent and the oceans we've seen impacts from the equator to the poles and from the coast to the mountains here's a map from the last IPCC report of the places that climate change impacts have been observed and attributed to human actions and we've seen impacts on natural systems we've seen impacts on biological systems and we've seen impacts on on human systems i'll just introduce you to a couple of the kinds so food production we can look at the global trajectories of crop yields for the all the major crops and we can figure out based on historical patterns whether the major crops like a little warmer or a little cooler where they've grown and what we see is that most of the major crops are now grown in areas where the warming that's already occurred has decreased yields that's been true for for wheat over the last several decades it's been true for barley over the last couple of decades it's been true for corn over the last couple of decades we have already seen less increase in yield climate change impacts on agriculture in the past 20 or 30 years fires one of the one of the clearest examples and how many of you from california okay well one of the things that that you really see is just a feature of california life unfortunately increasing is these horrific wildfires wildfires across the western u.s. have been increasing the the increase over the last 30 years has been about a 10-fold increase in area burn on an annual basis these are the the 20 biggest wildfires in california history in terms of the damage and these are the ones that have occurred in the last two years absolutely striking pattern and if you say how much of that is a consequence of warming that's already occurred you see this striking pattern where fuel dryness is substantially higher in the last few years and you can then feed that into a climate model and say okay well if we run counterfactual without warming how many fires would we have had and you get the the black line you say how many of we actually had is the the red line and the difference between those the component that's due to anthropogenic climate change is in the yellow line and that is telling us that we have now reached a point where the anthropogenic component of fire risk of area burned in the western u.s. is approximately the same as the as the natural component we have doubled fire risk in the last 30 years or so really striking pattern let's see there's one other element of the current impacts that is too important to pass up and and it's economic inequality so really beautiful work by Noah Diffenbaugh and Marshall Burke published earlier this year took advantage of the observation that in in most places that are currently cool if you look at the variation in economic activity with temperature historically you see that warm years yield to slightly higher economic output cool years lead to slightly lower in places that are currently hot warm years lead to slightly lower economic output and cool years lead to slightly higher if you simply feed those historical patterns into the climate changes that have occurred over the last several years what you see is that the climate change that we've seen in the last 30 or 40 years has dramatically increased economic inequality around the world because the countries that are currently hot are also the countries that are currently poor so what we've seen is that poverty in the hot parts of the world has been exacerbated by the climate changes that have already occurred and you can see that in the in the top two figures here where this is plotting percent change in in GDP per capita and if you look at the the left-hand figure from 1961 to 19 to 2010 you can see that across the equatorial band we've seen increases in GDP driven by the climate changes that are on the order of minus 20 to minus 40 percent where in cool parts of the world we're actually tending to be in the in the positive frame increasing in in economic inequality and that's what I wanted to speak about as the as the sort of social driver of the tipping point I'm going to stop here I'd love to take any questions and I wish you the very best with the energy at Stanford and with your work in solving this problem moving forward yeah let's see I don't know if you're on wait for the microphone or shout so yeah the last part um which is the slide that we're on was pretty interesting how you were able to correlate the temperature the temperatures of different regions to the economic prosperity um could you explain more how you like how you did the calculation how you how you get that yeah so this is a really beautiful powerful technique for microeconomics which essentially takes advantage of the fact that a year-to-year wiggles in temperature occur more or less independent of the other things like political dynamics and and global trends and so basically all you do is for every country in the world just say if it was a you know point 05 warmer this year what happened to GDP if it was 0.1 cooler what happened to GDP put those all into a big database and what you find is this pattern where for cool countries you know warmer years lead to increases for hot countries lead to decreases and then that that gives you this hump shaped response if you then put the hump shaped response into the actual historical trajectory of temperatures this is what you get so this is simply reading out the historical trends as they overlay the actual change in climate so it's not using the the trend in GDP and GDP in most of these countries that are shown in red has has continued to grow it's that the climate change impact has held it down below what it would have otherwise been could you speak into the microphone so i'm just curious what about the converse where um cooler countries get colder does it lead to lower growth where cold well i've colder countries aren't getting colder there they're getting warmer and you know that the the implication of the statistical pattern is that if colder countries were getting colder that it would hold back their growth as well of course the actual pattern is that the most rapid warming is occurring in these northern latitudes where the colder countries are and and in earlier work from this group it it turned out that the the temperature optimum for economic activity was about the annual average temperature of san francisco so for those of you who are not from california that's potentially good news but it also means that in california we're beginning to tip over the edge into the zone of of eroding economic growth with with warming i might be able to take one more question but i'm also right at the end of the time one more if you could wait one second for the microphone so you mentioned earlier the systemic inertia and obviously there's a lot of factors that go into that social political everything else but let's say tomorrow a miraculous consensus descends upon world leaders and we all decide this is something we're going to make a priority what do you think is a realistic timetable for how quickly we can correct course well the question of how much we want to spend i i think a fair way to think about this is that most entities are are really really opposed to early retirement of whatever the assets are so if someone built a coal fired power plant and they inaugurated it yesterday and it has a 40 year lifespan i think we can expect emissions from that plant maybe not 40 years but more than 30 uh every fossil fuel vehicle that is going to be produced next year we can expect to have a life of 10 to 15 years and i think it's the real driver of the maximum pace we can transition is going to be controlled by you know when's the last time we inaugurate the fossil fuel powered whatever into the economy and how long does that last one of the things you will hear quite a lot about in your experience at stanford is opportunities for carbon capture and storage and i think that there are some ways that we can begin to hold co2 out of the atmosphere but at least at this point the economics aren't pointing to those being the most attractive option thank you so much