Hi. It's Mary Sheehan, and we're going to talk now about a new special report of the intergovernmental panel on climate change titled Global Warming of 1.5 degrees Celsius. If you follow the press, you'll know this report heightened the urgency of action on climate change. So, we'll talk in this session about why this report was carried out? What are its findings and how it changes things? We've talked about the fact that the IPCC publishes synthesis reports regularly. Its last full assessment report AR5, on which this course is based, was issued in 2013/14, and the sixth assessment report is expected out in 2021 or 2022. So, the new report, which is nicknamed SR 1.5 was issued as a special interim report. Well, why? SR 1.5 was commissioned by parties to the 2015 Paris Agreement. As you recall, the Paris negotiators agreed to keep global warming to two degrees Celsius by the end of this century. By the way, throughout this course, we'll talk mainly in degree Celsius. Two degrees represents about 3.6 degrees Fahrenheit. The parties at Paris also agreed to the aspirational target of 1.5 degrees Celsius if possible. So, the main goal of this SR 1.5 report then was to better understand the differences between these two targets; between 1.5 and two degrees. So, SR 1.5 looks at three main questions: when will the threshold of 1.5 degrees be reached? What concretely are the differences and impacts between 1.5 compared to two degrees of warming? And can we limit warming to 1.5 degrees? If so how? So, we'll go through each of these questions briefly. So, SR 1.5 starts by updating previous work on how much global warming we have experienced so far. It finds that as of the end of 2017, Earth had warmed by about one degree since the start of the industrial era. Usually, what's meant by the industrial era is about 1850 to 1900. So, this map from the US National Oceanic and Atmospheric Administration, who's responsible for tracking extreme weather, shows billion-dollar weather and climate disasters occurring in 2017 in the United States. NOAA documented 17 different billion-dollar plus episodes of extreme temperature, storms, drought, floods, and wildfires that you see on the map. If we have this type of map, globally, we would see a similar pattern in many other parts of the world for 2017. In fact, 2017 extreme weather was a major reason some commentators have called 2018 the year the world woke up to climate change. So, is this map reminds us? We know that where we are now about one degrees Celsius of warming is already bad enough. Well, how much worse will it get, and when? SR 1.5 concludes that at the rate we're currently going, we'll likely breach 1.5 degrees Celsius somewhere between 2030 and 2052. So, as early as a decade or so from now and very likely within two decades. This is shown in the graphic from the report, where the orange highlighted section with the zigzagging trends shows observed global mean surface temperature increase from 1960 to the present. Then the grayish shaded area picks up and carries us out to the future. This gray shading represents several scenarios for modeled future global temperature change. In the most likely trajectory, which you see indicated by the red line there, Earth reaches 1.5 degrees of additional warming around 2040. If we look past this out to the end of the century, which is the Paris agreement's time frame, some scenarios remain around 1.5 degrees and some exceeded, but then returned to that level. So, this is important. What these scenarios suggest is that even though we'll reach 1.5 degrees warming soon, there are economic pathways that enable us to either remain at approximately this level, or at least to recover to this level up to the end of the century. So, is there really a difference between 1.5 and two degrees? This was the second question asked by the report. SR 1.5 concludes the risks are higher for global warming of 1.5 degrees than at present but lower than at two degrees, and this with high confidence. Well, this is a rather dry way of saying, half a degree seems small, but it's not. Yes, half a degree really matters. To illustrate this, we're going to look at 10 areas of risk identified in the new report and shown in this bar chart. The 10 areas include warm water corals, mangroves, fisheries, the Arctic land-based ecosystems, coastal and fluvial flooding, crops, tourism, and heat-related impacts on people. We can think of these as central indicators of risk to human and ecological systems from a changing climate. The legend shows that the darkest purple color on top of the bar is a zone of very high risk of widespread and potentially irreversible climate impacts. Whereas red is high risk of severe impacts, yellow is detectable impacts at moderate risk, while white represents no particular impact attributable to climate change. The wide gray line cutting across the chart horizontally shows where we've been over the last decade, sort of just under one degrees Celsius of warming. We see that the most acute risks have affected warm water corals, which is red to purple as the gray bar passes it. For the remaining nine risk areas, we've largely been in a yellowish zone that indicates detectable but more moderate climate-related risks. But so what's most relevant for us now is looking at the difference if we shift upwards on the y-axis and compare impacts at 1.5 with impacts at two degrees of warming. So, looking across the line for 1.5 degrees, we see a changed picture. We now have very high risk of potentially irreversible impacts for coral reefs, and severe impacts for fisheries, the Arctic, and coastal flooding. So, this already looks quite bad. But things moved from bad to worse. So, if we go up and look at the two-degree warming line and follow it across, we now see very high risk of severe, possibly irreversible impacts for corals, but also for the Arctic region and for coastal flooding. We see severe widespread risks for fisheries, terrestrial ecosystems and fluvial flooding, while crop yields and heat-related morbidity and mortality each are reaching a higher risk, orange to red zone. So, the takeaway here is that there is a stark difference between 1.5 and two degrees for most of these 10 risk areas. In particular, for some areas like coastal flooding, we may be moving quickly towards potentially irreversible impact. So, let's pause here for a moment. Since this is a public health course, it's worth noting that the health impacts of changes in these sentinel areas is profound. Six of the 10 risky areas are either directly or indirectly linked to human health and well-being. So, this includes looking left to right impaired sustainability of fisheries. Fish provides the main source of protein for several billion people in the world. The Arctic which is warming several times faster than the global average putting a whole culture at risk. Coastal and fluvial flooding, which are both worsening dramatically with sea level rise and precipitation, potentially making some areas uninhabitable and having direct health impacts through injuries on people. Crop yields which are failing with drought and extreme weather, with implications for hunger and famine. Heat-related mortality and morbidity rates which are increasing with global warming. So, let's just look briefly at the three risk areas which most directly impact human health and well-being: heat-related mortality and morbidity, and coastal and fluvial flooding. SR 1.5 details specific impacts, as we move from 1.5 to two degrees. So, the share of global population exposed to extreme heat, at least once every five years, would increase from 14 to 37 percent. So, this is more than a third of the world's population. Impacts would be particularly heartfelt in cities. The photo on the left is Phoenix, Arizona, one of the hottest cities in the US, where large number of deaths from extreme heat has been creating a public health crisis there. In terms of coastal flooding, an additional 10 centimeters of sea level rise at two degrees would increase the at-risk populations by around 15 percent. Small island nations in the Pacific and Caribbean, as well as coastal areas in many parts of the world, are now evaluating possible land loss and wondering how much population relocation will be needed. Then, fluvial or river flooding would also shift to higher risk at two degrees according to SR 1.5. We've seen the power of extreme precipitation to create river flooding. If this occurs in the context of a major coastal storm, we can see compound impacts that create more widespread flooding than would be the case with either coastal or fluvial flooding individually. So, this was the case, for example, with 2017's Hurricane Harvey in Houston, Texas, which is shown in the photo on the right. Increased fluvial flooding, or increased river flooding risk, along with severe coastal flooding risks will leave many cities worldwide increasingly subject to Harvey type compound impacts. So, if two degrees is so much worse including for population health outcomes, the obvious next question is, can we remain at 1.5 degrees? SR 1.5 suggests the answer is yes, but SR 1.5 emphasizes that we'll inevitably get to 1.5 degrees warming sooner or later. By reducing greenhouse gas emissions now, we can delay the moment it happens, perhaps to 2050 instead of 2030. This will help. It will give us time to adapt, time to develop technologies, for example, for removing carbon dioxide from the atmosphere. The problem is however, that with the current policies and economics activities, the report says we're headed for about three degrees of warming, by 2100. In other words, we are not at all on track to limit the increase to 1.5 degrees. In fact, as you see in the bar chart here from World Resources Institute based on the IPCC data, our current annual emissions globally, and they're shown here in gigatons of carbon equivalent per year, are in the order of two times the amount needed to be consistent with 1.5 degrees. So, to remain within the 1.5 degree level, we would need to cut annual emissions approximately in half by 2030, and then go even further and reach net zero carbon emissions by 2050. So, net zero carbon emissions means that any greenhouse gas emissions would be offset in some way, either by Carbon dioxide removal, or through measures that enhance carbon sinks such as reforestation. Which brings us to a follow up question, how quickly can we do this? How quickly can we transform? This graph from the IPCC report shows shaded areas representing the various scenarios of emissions reductions, and these are in billions of tons of carbon dioxide per year. That enable us to remain within the 1.5 degree target set by the end of the century, and different scenarios involve different mixes of policies and outcomes. Well the scenarios represented in blue mainly achieve 1.5 degrees. The gray shading, includes some scenarios that allow for an overshoot of 1.5 degrees and the need to reign in emissions afterwards, through carbon dioxide removal, either through technologies such as carbon capture and storage, or through other means. What's important to note here though, is that some impacts as we've seen particularly on sea level rise, for example, but also species extinctions may be irreversible in human time-frames. So, overshooting incurs this risk of potential irreparable damage. So, as the report emphasizes, its far better not to have to rely on overshooting scenarios, but remain at 1.5 degrees if possible. Overall, then the message of the SR 1.5 report is clear. Whether it's one decade or two, we have a narrow window in which to act to try to reduce carbon emissions, sufficient to maintain the net global warming increase to 1.5 degrees. Action is urgent and the magnitude of the change needed is unprecedented. It requires an economic transition with no documented historical precedent according to the report. So, given the need for such a strong economic transformation, SR 1.5 also asks, how will reducing greenhouse gas emissions affect sustainable development outcomes? Will it all be negative, or is there some scope for positive outcomes? It did this by connecting climate change mitigation and the sustainable development goals. So, the sustainable development goals, or SDGs, are set of 17 goals agreed to in 2015 as guides to national and international development, and the chart shows the relationship of greenhouse gas reductions with each of the SDGs, and the main emissions reduction strategies evaluated were in three categories. Energy supply initiatives on the left, like replacing their country's reliance on coal with solar energy. Energy demand initiatives, such as increasing the energy efficiency of industry, that's in the center. Then land use initiatives, for example, shifting from raising cattle to planting forests. For each sustainable development goal, we can think of mitigation as either bringing trade offs, and those are shaded in the brown tones, or bringing synergies, and these are shaded in blue tones. A classic example of a synergy in the health area, for example, would be when reduced emissions bring improved air quality that lowers respiratory and cardiovascular disease, therefore bringing health benefits. This slide shows just the first three of the SDGs. First in red is poverty, second in yellow is hunger, and third in green is health, and you'll find the full table of the 17 SDGs in the report. But what I'd like to point out here in the slide is that for health, the trade-offs in brown are relatively low, and the synergies in blue are fairly high. This suggests that there's substantial room for benefits to health with reductions in greenhouse gases, and this opens up many policy and communications options for improving public health with mitigation, that we'll talk about further in the course. Well, in moving toward wrapping up now, I'd like to take a minute to pause and to return to this question that we started with, "Why is this report important?", and I'd like to share with you some quotes gathered by The Guardian newspaper from several climate scientists, which can give you a perspective on SR 1.5 significance. The first quote is from James Hansen, one of the first climate scientists to explain the science and convey the dangers of climate change. You see him here in the photo carrying his message to the public and to policymakers, and developing awareness of the threats from a warming climate. Dr. Hansen said that this report, SR 1.5, showed that both 1.5 degrees and two degrees Celsius would take humanity into uncharted and dangerous territory, because they're both well above the Holocene era range in which human civilization developed. But he said that there was a huge difference between the two. 1.5 degrees Celsius, he said, gives young people and the next generation of fighting chance of getting back to the Holocene or close to it. That's probably necessary if we want to keep shorelines where they are and preserve our coastal cities. So, this image is one I'd like you to carry with you as we continue through the course. Dr. Hansen's commitment to communicating the message, and his view that 1.5 degrees Celsius maybe the only way to preserve our coastal cities. Then Johan Rockstrom who has also spoken widely in public about the risks of a changing climate for sustainable planetary health, including as shown in the photo here at a Ted Talk. Dr. Rockstrom, regarding this report noted that climate change is occurring earlier and more rapidly than expected. Even at one degree warming, it is painful already. This report is really important. It has a scientific robustness that shows that 1.5 degrees Celsius is not just a political concession. There's a growing recognition that two degrees is dangerous. So, it's another image that I'd like you to keep in mind as we go through the course. Dr. Rockstrom globe, and the growing recognition by scientists of how quickly we've moved towards dangerous outcomes. Finally, Jiang Kejun, one of the reports core authors said, "I hope this can change the world. Two years ago, even I didn't believe 1.5 degrees Celsius was possible. But when I look at the options, I have confidence it can be done. I want to use this report to do something big in China." So, this is one final image for you to carry with you Dr. Kejun's hope that we have time and the ability to change the world. As we'll see throughout the course, public health has tools that may be key to helping convince people that this hope is valid and that this change is needed. So, in summary, I think that this SR 1.5 report carries three big messages. Extreme alarm, a glimmer of hope, and a call to action. The situation is worse today at one degree Celsius than many scientists even imagined, and meanwhile, two degrees warming is now seen as more dangerous than four or five years ago. So, the climate is changing more quickly than many expected. What we've seen here is that half a degree on average really does make a difference, particularly when it comes to this idea of potentially irreversible impacts. But with this report, for the first time, we have something like a road map, a guide to tell us what to expect, when, and what may be needed to keep ourselves and the planet safe. We may have a slightly larger window than we previously thought to make changes, and many scientists are convinced that we have a chance of succeeding. Reducing greenhouse gas emissions also will bring some positive synergies. But the bottom line is that efforts now are crucial since the window is short, and it turns out that public health is on the frontline of the challenge. Health co-benefits from greenhouse gas reductions can be a powerful argument in support of mitigation, that can be employed with citizens and policymakers alike. Adaptation to parameters of a 1.5 degree warmer world, that would be hotter more storm and disaster-prone. This kind of adaptation is urgent. The main takeaway message is that it depends on all of us taking action. We all have to go back home and do something big with this report. Public Health, it turns out, can play a leadership role as we'll see in the rest of this course.
