Hi, welcome everyone. This is Brent Kim. I'm a researcher at the Johns Hopkins Center for a Livable Future. We'll be talking today about some of the greatest public health and ecological threats of our generation. I believe that many of you, the students listening to this lecture, will be an integral part of that solution, which is why I'm both excited and honored to share our latest research on sustainable diets and climate change with you. Throughout this lecture, I'd like you to keep the following questions in mind. First, what defines a sustainable diet? Second, why do sustainable diets matter? Third, what might sustainable diets look like in the US and around the world? Finally, fourth, how can we promote sustainable diets and sustainable agriculture? We won't be providing the answer to the fourth question in this lecture. Because I'd like that to be a conversation that we have together regardless, I'd like you to keep it in the back of your mind. Let's start with the background and rationale for sustainable diets. The United Nations Food and Agriculture Organization provides us with a helpful framework for defining what a sustainable diet is. Firstly, it must be ecologically sound and that's probably not a surprise to most of you, because when we think of sustainabilities, we usually think about the environment. However, it's not just about the environment, for a diet to be sustainable, it must also meet the nutritional needs of the population. It must be culturally acceptable and people must have both economic and physical access to the foods that comprise the diet. If you propose a diet that's great for the environment, it will not have traction if it does not meet the nutritional needs of the people who follow it, or if people can't access the foods or ingredients that are in that diet. Now these concerns are particularly relevant for many low and middle-income countries, which we'll discuss later. Since this lecture is predominantly about climate change, our focus will primarily be on the ecological component of sustainability. But I'd like you to keep these other criteria in mind. Climate change is among the greatest public health, economic and ecological threats to current and future generations. Heat waves, droughts, flooding and wildfires amount to an immeasurable burden on morbidity and mortality. I'm just going to use heat-related mortality as just one example of the impacts of climate change. This research study looked at heat waves in the Eastern United States in 2002 and projected out to 2057. In what we call, a business as usual scenario, which means, there is no dramatic action to curb the greenhouse gases that contribute to climate change. The redder areas on the map represent greater frequency on the top row and duration on the bottom row of heatwaves and on the bottom you can see the number of deaths attributable to those heatwaves. It's authors projected an estimated almost 20-fold increase in heat-related deaths if we fail to curb greenhouse gas emissions and that's just in the Eastern US. Many populations are also more likely to experience hydrological extremes. Periods of intense flooding alternating with periods of drought. This photo, for example, shows the devastation caused by Hurricane Maria in Dominica in 2017. Whether from storms, droughts, rising sea levels or rising food prices, many of the world's poorest will get hit by climate change the hardest. I'd like to give you a 30 second primer on the nuts and bolts of climate change or global warming. As shown in this illustration, radiation or heat energy from the sun strikes the Earth's atmosphere. What we don't see on the diagram is about 30 percent of that energy is reflected back into space. The rest of it goes through the atmosphere and hits the Earth's surface. Some of that solar energy is reflected back into space, and the rest is trapped in the atmosphere by the appropriately named greenhouse gases, effectively warming the planet. The term, "radiative forcing" describes the net balance between the solar energy coming in and the solar energy coming out. When the energy coming in, outweighs the energy coming out, we have positive radiative forcing, thus warming of the planet. Let's talk about the greenhouse gases that contribute to this warming phenomenon. Specifically, I like to look at some examples of greenhouse gases from the food and agricultural sectors, since we are talking about sustainable diets after all. I like to ask you if you can name any of those greenhouse gases. Feel free to pause this lecture, and see if we can come up with at least three, food-related greenhouse gases, and bonus points to you. Not actual bonus points on your grade, but kudos from me, if you can name the chemical formulas of those gases. In the next slide, I will reveal the answers in 3, 2, 1, here we go. Here we can see the three main greenhouse gases from the food system. From top to bottom they are carbon dioxide, some food system sources include the combustion of fossil fuels, and the clearing of forests. Trees are form of biomass that capture, store or sequester carbon from the atmosphere that would otherwise contribute to climate change. When you clear forests, you're releasing that sequestered carbon into the atmosphere, thus contributing to climate change. Below that, in row two we see methane. Examples of food systems sources of methane include livestock, and we'll talk about that in greater detail in the next section. Decomposing food waste in landfills, again the combustion of fossil fuels, and decomposing organic material in flooded rice paddies. In the third row, we have nitrous oxide. Some sources include the application of nitrogen fertilizer, as well as livestock which we'll discuss again in the next section. I just want to note that the examples we give here, are considered anthropogenic, meaning they result from human activity. There are other greenhouse gases, such as water vapor, believe it or not, that do contribute to the greenhouse gas effect. But because human activity has no measurable impact on water vapor, we do not consider that to be an anthropogenic greenhouse gas. I'd like to move to the third column, where we can see the concentration of these gases in parts per billion prior to industrialization. We can see that carbon dioxide was, and still is. If we move to the fourth column, the most prevalent greenhouse gas in the atmosphere and thus, it is the gas that contributes the most to climate change. We can see the dramatic rise in the concentrations of all three greenhouse gases, between the pre-industrial times shown in the third column, and around 2013-2015, shown in the fourth column. Those increases are certainly cause for concern, from a climate change perspective. Now, not all greenhouse gases are created equal, and I'm going to explain what I mean by that. Take a look at the fifth column. The fifth column shows the atmospheric lifetime of each gas in years. The atmospheric lifetime of carbon dioxide is a little tricky to measure, but it's generally considered that it remains in the atmosphere for centuries. Compare that to methane, which only remains in the atmosphere for about 12 years, and then nitrous oxide about a 121 years or so. Once carbon dioxide is up there, it's got to stay. Whereas methane, has a relatively short lifespan. Now does that mean we don't need to worry about methane?. We'll take a look at the next column. Global warming potential. This is a measure that scientists use to standardize the warming impact of each gas, as if it were the same mass of carbon dioxide. For example, take a look at methane, it has a global warming potential of 84. That means, compared to the equivalent mass of carbon dioxide, the same amount of methane warms the planet 84 times as much. Then nitrous oxide we see has a global warming potential of 264. The same mass of nitrous oxide is much more potent, than carbon dioxide in terms of its contributions to global warming. Note that there are two columns for global warming potential. On the left, we have the global warming potential over a 20-year period and on the right, we have the global warming potential over a 100-year period. We could have GWP200, 500 or even 1000. We need these different measures of global warming potential because of the fact that the gases have different atmospheric lifetimes. Take a look at methane again. Remember it's not in the atmosphere for very long, relative to carbon dioxide. That's why the global warming potential of methane is pretty high in the short-term, but if you look at it over a 100 year span, it drops down to 28. That's because over that time span of a 100 years, much of that methane will have broken down and will no longer be contributing to global warming. The take-home message here is that gases like methane are much more potent in the short-term. Whereas gases like carbon dioxide per unit of mass, do not contribute as much to global warming, but it remains in the atmosphere for a much longer period of time. There are two other food system greenhouse gases of note that I like to point out on the bottom two rows, and those are chlorofluorocarbons and hydrochlorofluorocarbons, CFCs and HCFCs. Both of those, they're not agricultural, but they are coolants used in refrigerants and we do refrigerate our foods, so this is relevant to the food system. I point them out because, wow, look over to the very right, look at the global warming potential of those refrigerants, 10000 times that of carbon dioxide. Even though there's not a lot of these in the atmosphere, a small amount goes a long way toward warming the planet. Now there's some bad news, there is some good news, and then there's going to be more bad news again. Let me start with the first bad news, so the first bad news is that, not only do these two gases contribute heavily to climate change, they also deplete the ozone layer. That's the bad news. Now some good news. Both of those gases were banned because they were found to be harmful to the ozone layer. But now we have some new bad news, which is that those two refrigerants have been replaced with a new refrigerant, HFC 23 is an example of one, that it does not damage the ozone layer, it has an enormous global warming potential, almost 13000 times that of the same mass of carbon dioxide. This is one of those tricky situations where if we're not careful, we end up solving one problem and creating two or three others. This is why Systems thinking is so important, considering the relationships and dynamics among all of these different actors in the food system. Now, I do have a little bit of good news on top of the bad news and the good news, and that is, while there has been no federal action to curb hydro-fluorocarbons in the US, there are a number of states which either already have or are working on phasing out these gases. Surprisingly, there is a recent report called Project Drawdown that identified the most impactful interventions we can make as a civilization to curb climate change. Number one on their list, it wasn't to stop driving, although that's important too, it wasn't a curb international flights, although that was near the top too. It wasn't moving toward plant-based diets, although we'll see that's very important. The number one top priority for addressing climate change according to this report, was to phase out these refrigerants, because of their enormous global warming potential. Where do we need to be as a civilization to avoid the most catastrophic climate change scenarios? Global leaders and scientists have all agreed that we have to cap global average temperature rise at or below 1.5 degrees Celsius relative to pre-industrial temperatures. Unfortunately, it's looking like we're not on track for that goal. For the purposes of this lecture, we're going to use the less ambitious but more feasible target of capping global average temperature rise at two degrees Celsius relative to pre-industrial temperatures. This graph shows the contributions of different sectors to global greenhouse gas emissions. The y axis represents gigatons of carbon dioxide equivalents per year. Remember earlier, we talked about how not all greenhouse gases are created equal. Carbon dioxide equivalence is a way to standardize all of those different gases in terms of their warming potential relative to carbon dioxide. The bottom portion of the stacked bar on the left, shows the global contributions of agriculture to greenhouse gas emissions in 2010. On top of agriculture, we can see the contributions of all of the other sectors, industry, transportation, energy use, and so on, to climate change in 2010. If we move over to the right, we can see the greenhouse gas emissions from agriculture under a business as usual scenario. In this case, global meat and dairy intake continues to rise as projected, and here we see a projection for 2050. The dashed red line above that, is the threshold for the year 2050 for all sectors for greenhouse gas emissions that we must stay below if we want to have at least a two-thirds shot of keeping global warming below that two degree Celsius increase that we just talked about. Now I will ask you what is wrong with this picture? If we take the emissions from all of the other sectors in 2010, it's clear that we need to dramatically reduce them in order to stay below the threshold. We have to cut back on international flights, we urgently need to decarbonize the energy grid and move to renewables, we need to shift to public transportation. All of these things urgently need to happen. The challenge is that, no matter how much we reduced the top section of that stacked bar, there is no way we're going to be able to squeeze it in between the top of agriculture's emissions in 2050 in that threshold, we're going to be way above that threshold and deep into the territory of catastrophic climate change. Yes, we absolutely need to cut back on flying shifted public transit, adopt renewable energy, but if we do all of those things and we don't also address the contributions of the food system and agriculture we will be way above that line. That sounds pretty grim, but there is some hope. The same series of research papers which we reviewed in the source below, showed that a 75 percent global reduction in meat and dairy intake, would shave off about 7.4 gigatons from agriculture's greenhouse gas emissions in 2050. On top of that, if we reduce global food waste by 50 percent that would shave off another 4.5 gigatons, and finally, this isn't shown, but if we adopt certain technological interventions we could shave off another gigaton or two. Now this scenario is looking a little bit more hopeful you can imagine with agriculture's emissions shrunk down low enough, if we can also shrink down the greenhouse gas emissions from all those other sectors, we might be able to stack those bars on top of each other and still be below that threshold, which is where we absolutely have to be below that threshold. I'm going to give you another example that reinforces that point. The best minds at Harvard and Oxford and all the top research universities in the world put their heads together and attempted to answer the question, where is the food system headed? where do we need to be? and what do we need to do to get there? Here we see an example for climate change, the Y axis of this chart shows the greenhouse gas emissions from food and agriculture relative to where we are now in terms of percentages, so where it says 100 that's where we are right now. The red bar on the left shows where we will be in 2050, again, under a business as usual scenario, and you can see that the greenhouse gas emissions from food and agriculture are projected to increase by over 80 percent relative to where we are now. Note that the authors divided this figure into three horizontal sections, and the top in the red is the danger zone, that's where we overshoot that two-degree threshold for climate change and we're deep in the territory of catastrophic scenarios. The middle slice is caution, maybe we'll be okay, maybe we won't, and the green area is what they determined to be the safe zone, that's the area where we have a livable future. What do we need to do to get down into the safe zone? The second bar on the left in yellow shows how much we can reduce global food system greenhouse gas emissions by cutting food waste. The third bar in gray shows how much we can reduce food system greenhouse gas emissions with technological interventions. The fourth bar in green shows how much we could reduce global greenhouse gas emissions in 2050 by adopting a flexitarian or mostly plant-based diet. Note that no three of those single interventions gets us into the green zone, however, all three of them combined, shown in the blue bar in the right can get us into the green zone by 2050, and this is the message I want to hammer home. These are the three interventions that we need and we saw it in the last chart too, we need a shift toward plant-based diets, we need to dramatically curb wasted food and we did a little bit of help from technology, and we need all three of those things working together to hopefully get us in the green zone. These other parts of the figure illustrate the exact same point, but instead of for greenhouse gas emissions, we can see what we need to do to get into the safe zone for global land-use, freshwater use, and nitrogen and phosphorus application which are measures of water pollution. Note that for some of these outcomes, the best we can do is get into the yellow but we need to do the best that we can. To wrap up sustainable diets, it's more than just the environment, they must also be nutritionally viable, culturally acceptable, and people must have physical and economic access to the foods and ingredients. We talked about how greenhouse gases vary in terms of their global warming potential and the time they remain in the atmosphere, and finally, to remain within planetary boundaries we need the combination of a dramatic global shift toward plant forward diets, reductions in wasted food with a little bit of help for technology.
