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7o p e n i n g p l e n a r y s e s s i o n Keynote Presentation 2 the Changing Climate: the sCienCe and how it affeCts transPortation Donald Wuebbles Donald Wuebbles provided an overview of the science of climate change and how climate change could affect the transportation sector. He suggested that climate change was one of the most important issues facing humanity. He expressed interest in communicating information on climate change science in a way that assists transporta- tion professionals in assessing the vulnerability of the transportation system. Wuebbles reported that scientists continue to reevalu- ate the understanding of the science of climate change. He noted that two recent reports provide current assess- ments of climate change. The first report, Climate Change 2013: The Physical Science Basis, by the Inter- national Intergovernmental Panel on Climate Change (IPCC), is available online at http://www.ipcc.ch/report/ ar5/wg1/. Wuebbles was a coordinating lead author of Chapter 1 in this report. The second report, Climate Change Impacts in the United States, is the third U.S. National Climate Assessment (NCA), sponsored by the U.S. Global Change Research Program; it is available online at http://nca2014.globalchange.gov. Wuebbles summarized the current assessments of the science of climate change based primarily on these docu- ments. He reported these assessments indicate that cli- mate change is happening, that it is happening now, and that it is happening extremely rapidly. He further noted that climate change occurs largely because of human activities, but that many actions can be taken both to reduce future climate changes and to adapt to those changes that cannot be prevented. Wuebbles noted that observational records clearly indicate that the global climate is changing. He observed that increasing temperatures were just one of many indi- cators of climate change. Other indicators include sea level rise and the decline in glaciers, snow cover, and sea ice. The two reports document temperature increases in both the atmosphere and the oceans. He noted that three major groups worldwide monitor temperatures on a daily basis and analyze changes independently. All three groups have observed an increase of almost 1Â°C over the past century. He noted that 2015 was the warmest year on record and 2014 was the second-warmest year, fol- lowed by 2010, 2013, 1998, and 2009. Wuebbles discussed the importance of examining temperature on a decadal time scale, as climate change is the long-term variation in weather. He noted that each of the past three decades has been successively warmer at the Earthâs surface than any preceding decade since 1850. Further, in the northern hemisphere, 1983â2012 was likely the warmest 30-year period in at least the past 1,400 years. The IPCC report further illustrates global temperature differences from 1901 to 2012. He noted that almost all areas of the world are experiencing warmer temperatures, with the Artic countries facing the largest warming changes. As a result, the IPCC concluded that warming of the climate system is unequivocal. Wuebbles also described global trends in annual pre- cipitation from 1951 to 2010. He noted that there has been a slight, but not significant, increase in precipitation overall. In a general sense, wetter areas are tending to become wetter and dryer areas are tending to become dryer. He commented that these trends are evident in the southwestern United States and in the Mediterranean region in Europe. Wuebbles reported that since 1980, events that affect the U.S. economy by $1 billion or more have been tracked by the National Oceanic and Atmospheric Administra- tion. The number of $1 billion events related to weather and climate has increased. Weather-related events include droughts and heat waves, hurricanes and tropical storms, winter storms and crop freezes, flooding, wildfires, and severe local storms. There were 151 weather-related events exceeding $1 billion from 1980 to 2013. Accord- ing to Wuebbles, based on Munich Reinsurance Group (Re)analyses, similar trends are occurring worldwide. The number of weather-related events (on climate time scales) is increasing, as are the costs associated with those events. Wuebbles described the basics of the Earthâs climate system as illustrated in Figure 1. He noted that the sur- vival of life on Earth is based on solar radiation, which penetrates through the atmosphere. The sunâs radia- tion is absorbed by the Earthâs surface. Greenhouse gases (GHGs) keep some of the radiation from escaping into space, or the Earth would be approximately 30Â°C cooler, a frozen planet. He commented that GHGs can be thought of as providing a blanket around the Earth, keeping it warm to sustain life as we know it. He noted that the increase in some GHGs, including carbon diox- ide (CO2), methane (CH4), and nitrous oxide (N2O), results in even less radiation going to space, which results in the warming of the Earth. Wuebbles noted that natural variability also affects the Earthâs climate, but that the variability is not large compared with the changes in climate being observed. Natural factors influencing climate include variations in the Earthâs orbit and energy received from the sun, as well as stratospheric aerosols from volcanic eruptions. Human factors also influence changes in GHGs and the Earthâs temperature. Wuebbles described the process of examining the bubbles in ice core samples from Antarctica to measure
8 t r a n s p o r t a t i o n r e s i l i e n c e changes in CO2 over the past 800,000 years. He high- lighted some of the typical oscillations, but noted that the atmospheric concentrations of CO2, CH4, and N2O have recently increased to levels unprecedented in at least the past 800,000 years. Wuebbles discussed an analysis by the IPCC showing the influence of human behavior on the increase in tem- peratures. The observed global mean temperature warm- ing from 1951 to 2010 is approximately 0.6Â°C to 0.7Â°C. He noted that accounting only for the changes in GHGs and their effect on the climate system would probably overestimate the change. He reported that there is a net cooling effect from certain particles in the atmosphere emitted from human activities, however, and combining both into the anthropogenic forcing results in the change in temperature that would have been expected. Because changes in solar flux or from natural variability are too small to explain the observed temperature change, the IPCC concluded that it is extremely likely (greater than 95% in certainty) that human influence has been the dominant cause of the observed warming since the mid- 20th century. Wuebbles discussed projections for future average global surface temperatures. He noted that continuing heavy use of fossil fuels could result in at least another 4Â°C increase in temperature by the end of the century, in addition to the 1Â°C increase that has already occurred. Major reductions in the use of fossil fuels would be needed to realize an increase of only 2Â°C by 2100 (rela- tive to the preindustrial climate). He noted that the recently developed agreement in Paris calls for 2Â°C, but that we should aim for a 1.5Â°C target, if possible. He added that the GHG emissions that have already been generated will influence changes over the next 20 years, but that the choices made today are important for influ- encing trends by 2100. Wuebbles described changes in the average precipita- tion from 1986 to 2005 and then for the future low- and high-precipitation scenarios for 2081 to 2100. The sce- narios indicated that the contrast in precipitation between wet and dry regions and between wet and dry seasons will increase. Wuebbles described trends in extreme weather events. He noted that there is high confidence that the frequency and magnitude of extreme-heat tem- perature events, both individual days and multiday heat waves, are increasing. In general, the risk of extreme cold is decreasing. The frequency of extreme precipitation, including both rain and snow, is increasing worldwide. - FIGURE 1 Earthâs greenhouse effect (1).
9o p e n i n g p l e n a r y s e s s i o n In the United States, the risk of floods in some areas is increasing, and the severity of drought is increasing in some areas as warmer temperatures increase evaporation rates. Hurricanes are becoming more intense. He noted that these observed trends are consistent with basic phys- ics, historical simulations, and future projections. In terms of other types of extreme events, Wuebbles noted that there is moderate confidence that midlatitude storms will become more intense, storm surges will get stronger, and wildfires in the western United States will become a greater concern, with larger areas burned. He also noted that individual extreme events are being affected by human-induced climate change. He cited the current California drought and the 2003 European heat wave as examples. He noted that formal detection and attribution studies, supported by basic physics and/or future projections, show evidence of human interference with these events. Wuebbles described a few areas in which there is not enough information to fully assess the long-term impacts of climate change. Examples of these areas include the increased risk of severe winters due a slowdown in the jet stream, changes in hurricane frequency, and the impacts on small-scale extreme events including supercell thun- derstorms, tornadoes, ice storms, hail, and straight-line wind events. He noted that the latest science suggests that tornadoes will increase in number and in intensity. Wuebbles discussed past and projected changes in global sea level, citing information from the 2014 U.S. NCA, which projected an increase of 1 to 4 feet by the end of the century. Risk analyses should consider as high as 2 meters (over 6 feet 6 inches). He noted that the latest analyses, based on new understanding of potential ice losses in Antarctica, suggest that the high end may not be high enough. He also noted that the next NCA is just beginning and that he is coleading the climate science report. Wuebbles reviewed some of the impacts of climate change on transportation reliability and capacity. He noted that the 2014 NCA included a chapter on trans- portation and summarized topics presented in that chap- ter. The report notes that sea level rise and storm surge, extreme weather events, higher temperatures and heat waves, precipitation changes, Arctic warming, and other climatic conditions are already affecting the reliability and capacity of transportation systems in many ways. He highlighted an example of roads buckling from extreme high temperatures in Norfolk, Virginia, and described a study from Chicago, Illinois, that identified concerns with the impact of high temperatures on roadways and rails. He also noted that flash flooding resulting from extreme rainfall causes problems for freeways and road- ways and cited recent examples in Texas. Another key finding in the chapter described by Wuebbles was that sea level rise, coupled with storm surge, will continue to increase the risk of major coastal impacts on transportation infrastructure, including both temporary and permanent flooding of airports, ports and harbors, roads, rail lines, tunnels, and bridges. An example included in the chapter is the vulnerability of the Gulf Coast transportation hubs in Houston, Texas; New Orleans, Louisiana; and Mobile, Alabama. Within this century, 2,400 miles of major roadways are projected to be inundated by sea level rise in the Gulf Coast region. Roadways at risk in the event of a sea level rise of about 4 feet, which is within the range of projections for this region in this century, include 24% of the Interstate highway miles and 28% of secondary road miles. Wuebbles reported that another finding in the chap- ter was that extreme weather events currently disrupt transportation networks throughout the world and that projections indicate that such disruptions will increase. He illustrated this point with the destruction of roads in Vermont due to heavy rains and flooding from Super- storm Sandy. Wuebbles cited information from the Federal Avia- tion Administration on the vulnerability of airports in the United States to storm surge. According to this agency, 13 of the nationâs 47 largest airports have at least one runway with an elevation within the reach of a moderate to high storm surge. Wuebbles discussed some of the severe weather effects on aviation. He noted that it is already known that severe weather has major effects on aircraft operations, especially flight patterns. He suggested that as climate change leads to an increased incidence and changes in the intensity of severe weather events there will be many other impacts on aviation. As a result, he noted that improved severe-weather forecasting will become even more important than it already is. Examples of these impacts include increases in turbulence and climate vari- ability, convection, fog, and visibility and ceiling, which affect aviation route decisions. Higher temperatures and more heat waves will affect runway pavement, and sea level rise and storm surge will affect airport facilities and operations. Wuebbles discussed possible costs to the transporta- tion system from climate change and adaptation options. He suggested that climate change impacts will increase the total costs to the transportation systems and their users, but these impacts can be reduced through rerout- ing, mode change, and a wide range of adaptive actions. He discussed Figure 2 from the last NCA. He noted that many of the projected climate change impacts and resulting consequences on transporta- tion systems can be reduced through a combination of infrastructure modifications, improved informa- tion systems, and policy changes. He commented that Gerry Schwartz added the boxes highlighting the