Hello, it's Mary Sheehan, and we're going to continue with climate science, and this time take a look ahead. I will walk through the projections for the future climate under different scenarios, and we will continue to rely principally on the most recent assessment report of the Intergovernmental Panel on Climate Change or IPCC. As well as the United States Climate Science special report for its fourth climate assessment. The goal will be to better understand what the World Bank has called the new climate normal, and ways in which the future climate is likely to be different than the one we have now. This will help us understand opportunities for both mitigation and adaptation to better protect public health at the local level. We have talked about the conclusions of the Intergovernmental Panel on Climate Change, an increase of about one degree Celsius since the industrial era and the unevenly felt across the globe, with an additional amount of warming locked in due to the longevity of greenhouse gases in the atmosphere. We have further talked about the idea that this warming is extremely likely to be driven by human activity. In another way of expressing the same idea, the recent US climate science report concluded that there is no convincing alternative explanation for global warming other than human activity. Both of these reports project future climate conditions based on scenarios related to human activity and its impact on global warming, and we will look at both in this lecture. To model future climate, the Intergovernmental Panel on Climate Change used four standardized Representative Concentration Pathways. Each associated with a particular level of carbon dioxide equivalent emissions measured in parts per million. As shown in the table, these vary from 421 parts per million in 2,100 a best-case scenario of maximum effort to mitigate or reduce greenhouse gas emissions. All the way to the least optimistic scenario or a business as usual case with little mitigation that takes greenhouse gas emissions to 936 parts per million of carbon dioxide equivalent. Also included are two mid-range scenarios. Each of these four scenarios are associated with a modeled amount of radiative forcing or warming influence that contributes to continued global warming as shown in the graph. What this translates to in the medium term or 2,050 are differences in temperature increase that are not that large across scenarios, ranging from one degree Celsius and the low case to two degrees and the high case. However, in the longer term out to 2,100, the differences are more stark between a one degree Celsius in the best-case scenario and nearly four degrees Celsius in the more pessimistic case. This provides some perspective to the internationally agreed target of two degrees Celsius of warming, or even 1.5 degrees of warming if possible, the goal agreed at the Paris Accord. Under the strong mitigation scenario, this goal is achievable. Similarly, for sea level rise, the medium term differences in the low compared to high cases are not projected to be as large as the differences are in the longer term. Now, we will look at each of the major climate parameters in a bit more detail. In the case of heat, regardless of scenario, temperature change will not affect regions uniformly. Warming is projected to be greatest in the Arctic, as well as in the tropics, and subtropics. The frequency and intensity of very hot days, and nights, and the frequency and intensity of heat waves will increase. The number of cold days and cold nights will decrease. Precipitation will increase in frequency and in intensity over landmasses with tropical cyclone activity in regions where it occurs, such as the Atlantic and South Pacific and Indian oceans, is expected to be more intense and the storm tracks are expected to shift poleward. Increased precipitation and storm intensity will lead to greater storm surges in coastal areas. Meanwhile, arid regions, particularly across the earth's mid-latitudes will experience less rain, increased drought, and risk of wildfires. Ocean temperatures will continue to rise with the Gulf Stream likely weakening. Sea level will continue to rise as well with projections ranging from one to as much as 2.5 meters in places by the end of the century. This rise will increase the frequency and intensity of flooding from coastal storms. These projections are sensitive to the impact of abrupt or non-linear changes in the patterns of glacier melt, and particularly the Greenland and Antarctic ice sheets. So, in summary, climate scenarios for the future are based on differing assumptions about greenhouse gas emissions, from a strong mitigation effort to a business as usual lower mitigation effort. With strong mitigation of greenhouse gases remaining below the internationally set target of two degrees Celsius may be achievable. However, Earth's surface temperature and sea level will continue to rise in all scenarios, although the differences across scenarios are more marked in the longer term out to 2,100. Importantly, changes will not be evenly felt across the globe. The hardest hit will be those who are most exposed and most vulnerable. Cities where there are large concentrated populations and frequent location on coasts and rivers, are particularly on the front line of effects we've discussed such as more frequent and intense heat waves and more intense storms. In many cases, it is likely to be the poorest and most disadvantaged who are at greatest risk. Regardless, adaptation of local public health systems to a new climate normal will be needed to protect populations from extreme weather in virtually all parts of the world.