Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
2 The Challenge of Global Warming A ccording to the available evidence, the second half of the 20th century was warmer than any other 50-year period in the last 500 years, and probably in the last 1,300 years, Ged Davis said at the summit. The 20th century saw about a 0.6-degree centigrade increase (about 1.1 degrees Fahren- heit) in global and ocean temperatures (Figure 2.1). Over that same period, sea level rose about 150 millimeters (6 inches), and it is continuing to rise at about 3 millimeters (an eighth of an inch) per year. Mountain glaciers and snow cover have on average declined in both hemispheres. These global changes appear to be a consequence of changes in land use and energy use during the 20th century, Davis said. Deforestation and the burning of fossil fuels have increased the amount of carbon dioxide in the atmosphere from about 300 parts per million in 1900 to about 380 parts per million today. This increase has been driven by a fourfold increase in global populationâto more than 6 billionâcombined with an increase in the per capita use of energy. Given that per capita global incomes have risen some 10-fold since the beginning of the 20th century, the world has seen a 40-fold increase in economic activity. Energy use has not risen as fast as economic activity, owing to increases in efficiency and changes in the nature of economic activity. But Davis estimated that annual global energy use has probably risen at least 20-fold over the past century. The Intergovernmental Panel on Climate Change (IPCC) models that predict temperatures based only on natural forcingsâsuch as changes in solar output and volcanic activityâshow relatively moderate temperature changes over the 20th century (Figure 2.2). IPCC models that include the effects of 11
12 THE NATIONAL ACADEMIES SUMMIT ON AMERICAâS ENERGY FUTURE Difference from 1961 to 1990 (mm) FIGURE 2.1â Global air and ocean temperatures and sea level have risen over the course Figure 2-1.eps of the 20th century, while average annual snow cover in the Northern Hemisphere has declined. SOURCE: IPCC (2007; Figure 1-1). bitmap image low resolution anthropogenic greenhouse gas emissions show an increase in temperatures that closely tracks observations. SCENARIOS OF FUTURE CLIMATE CHANGE On the basis of models that assume different technology, economic, and policy trajectories, the IPCC has developed several scenarios of future emis-
Global Global Land Global Ocean 1.0 1.0 1.0 0.5 0.5 0.5 0.0 0.0 0.0 Temperature anomaly (Â°C) Temperature anomaly (Â°C) Temperature anomaly (Â°C) 1900 1950 2000 1900 1950 2000 1900 1950 2000 Year Year Year models using only natural forcings observations models using both natural and anthropogenic forcings FIGURE 2.2â Models that incorporate both natural and human causes of climate change more accurately predict temperatures over the past century as shown by the fit between the predictions of such models 2-2.eps and observed temperatures (black lines). SOURCE: Figure (upper bands) IPCC (2007; Figure 2-5). redrawn to vector 13
14 THE NATIONAL ACADEMIES SUMMIT ON AMERICAâS ENERGY FUTURE A2 A1B 20th B1 century Year 2000 Constant Concentrations FIGURE 2.3â Temperature increases in the 21st century are very likely to be larger than Figure 2-3.eps those observed in the 20th century according to scenarios developed by the Intergov- broadside ernmental Panel on Climate Change. For definitions of scenarios B1 and A1F1 at each mostly bitmap image low resolution end of the range, see the main text. SOURCE: IPCC (2007; Figure 3-2). sions (Figure 2.3). A low-emission scenario, B1, assumes a mid-century peak in global population, the rapid development of a services-oriented economy, and a change toward clean and efficient energy technologies. A high-emission scenario, A1FI, assumes a mid-century peak in population, rapid economic growth, and intensive use of fossil fuels for energy. Other scenarios fall between those two extremes. Even if all use of fossil fuels were to cease today, these models predict another 0.6-degree centigrade increase in temperature during the 21st cen- tury, Davis observed. Since all of the IPCC scenarios assume continued use of fossil fuels, all of the scenarios assume temperature increases larger than that amount. The most positive scenario (B1) results in model predictions of a 1.5- to 2-degree centigrade (2.7- to 3.6-degree Fahrenheit) temperature increase over the 21st century. This scenario is almost certainly overoptimistic, according to Davis. With a more balanced mix of assumptions (scenario A1B), an additional 1-degree centigrade (1.8-degree Fahrenheit) increase occurs. As a result, the models predict a 2- to 3-degree centigrade (3.6- to 5.4-degree Fahrenheit) increase in global temperatures.
THE CHALLENGE OF GLOBAL WARMING 15 In the most extreme scenarios, the models predict that temperature increases would be much larger. If China and India rely heavily on coal until the middle of the century for electricity, temperatures could, the models predict, go up 5 degrees centigrade (9 degrees Fahrenheit) or more. Temperature increases are, in turn, predicted to have major impacts on water, ecosystems, food, coastal areas, and health, Davis observed (Figure 2.4). Water supplies are predicted to dwindle in some areas, which could lead to human suffering and interregional tensions. Many ecosystems could be devas- tated, greatly reducing the benefits those ecosystems provide to human societ- ies. Agriculture could suffer in areas where the climate becomes more severe, coastal areas could be more vulnerable to flooding and loss of wetlands, and the burden of disease could grow. Already, problems are intensifying in mountain- ous regions, the Arctic, regions subject to drought, and low-lying areas. Davis emphasized that some uncertainties continue to surround the projec- tions of temperature increases. âModels are evolving and developing, and weâre dealing with complex dynamic systems that play out over one or two centuries,â he said. These uncertainties could lead to less warming than expected, but they also could lead to more. Also, other possible environmental effects linked to greenhouse gas emis- sions could prove to be serious, even if they are not much discussed currently. For example, Richard Meserve noted that about one-third of the carbon diox- ide that is released into the atmosphere is absorbed into the oceans. When it is absorbed, it is converted into carbonic acid, which increases the acidity of the oceans. This acidification of the ocean interferes with the ability of some organisms to take up calcium carbonate and use it in their shells and skeletons. Over time, this effect could provoke a worldwide crisis for corals and other organisms. The acidification of the ocean is already being observed, and models predict that this process will continue throughout the 21st century. Another potential unanticipated consequence involves the biological pro- ductivity of the oceans. Satellite readings of the oceans have revealed that large areas of the ocean have less plankton than they did previously, Meserve said. These âoceanic desertsâ appear to result from reduced upwelling of deep nutri- ent-rich waters to the surface. Each year the area so affected increases by about the size of Texas. âThe problem is growing more severe, with adverse impacts that are perhaps somewhat different and certainly occurring much more quickly than we had perhaps anticipated as recently as 3 or 4 years ago.â STEPS TO BE TAKEN Without major policy changes, emissions of carbon dioxide will continue to increase in future years. In the IPCC scenario that assumes no policy inter- ventions for reducing greenhouse gas emissions (the âreference scenarioâ in Figure 2.5), the total global emissions of carbon dioxide as a result of energy
16 Global mean annual temperature change relative to 1980-1999 (Â°C) 0 1 2 3 4 5 Â°C Increased water availability in moist tropics and high latitudes WATER Decreasing water availability and increasing drought in mid-latitudes and semi-arid low latitudes Hundreds of millions of people exposed to increased water stress Up to 30% of species at Significantâ extinctions increasing risk of extinction around the globe Increased coral bleaching Most corals bleached Widespread coral mortality ECOSYSTEMS Terrestrial biosphere tends toward a net carbon source as: ~15% ~40% of ecosystems affected Increasing species range shifts and wildfire risk Ecosystem changes due to weakening of the meridional overturning circulation Complex, localised negative impacts on small holders, subsistence farmers, and fishers Tendencies for cereal productivity Productivity of all cereals FOOD to decrease in low latitudes decreases in low latitudes Tendencies for some cereal productivity Cereal productivity to to increase at mid- to high latitudes decrease in some regions Increased damage from floods and storms About 30% of global COASTS coastal wetlands lostâ¡ Millions more people could experience coastal flooding each year Increasing burden from malnutrition, diarrhoeal, cardio-respiratory, and infectious diseases Increased morbidity and mortality from heat waves, floods, and droughts HEALTH Changed distribution of some disease vectors Substantial burden on health services 0 1 2 3 4 5 Â°C Global mean annual temperature change relative to 1980-1999 (Â°C) FIGURE 2.4â Temperature increases will have major impacts on theFigure 2-4.eps environment, agriculture, and human health. â âSignificantâ is defined here as more than 40 percent. â¡Based on average rate of sea level rise of 4.2 millimeters per year from 2000 to 2080. SOURCE: IPCC (2007; broadside Figure 3-6). redrawn (except boxed material on right)
THE CHALLENGE OF GLOBAL WARMING 17 50 45 Reference Scenario 42 Gt 40 19% Billion metric tons 35 34 Gt 30 27 Gt Alternative Policy Scenario 45% 25 Target 450 ppm 23 Gt 20 15 10 1980 1990 2000 2010 2020 2030 FIGURE 2.5â Without governmental policies to protect against climate change, carbon dioxide emissions will increase from 272-5.eps tons (shown as Gt) today to 42 Figure billion metric billion metric tons by 2030. SOURCE: IEA (2007; Figure 5.1, p. 192). use rise from 27 billion metric tons today to 42 billion metric tons by 2030. Furthermore, the current mix of energy sources in most countries is unlikely to change, Davis observed. Indeed, in some countries, the percentage of fossil fuels in their energy mix is likely to increase. Various policy initiatives discussed in the rest of this summary will be needed to reduce carbon dioxide emissions. Stabilizing concentrations of car- bon dioxide in the atmosphere will be an even greater challenge, Davis said. Emissions reductions that occur as a result of the Energy Independence and Security Act of 2007 (which is discussed in part IV of this summary) are âjust a little drop in the ocean.â To avoid dangerous levels of climate change, action must begin soon, Davis said, especially given the investments that must be made in energy infrastruc- ture. Retrofitting equipment that is already in place will be very expensive. At least $1 trillion of investment will be needed per year to achieve a low-carbon future, according to estimates Davis cited. In a $60 trillion per year global economy, that investment may sound achievable. But âmany did not expect to put that sort of money into energy capital,â Davis pointed out. Furthermore, trends in the release of greenhouse gases are headed in the wrong direction. Meserve described a recent study (Raupach et al., 2007) that found that the rate at which carbon dioxide is accumulating in the atmosphere accelerated from about 1 percent during the 1990s to an estimated 3 percent since the year 2000. According to the study, 60 percent of that increase is the
18 THE NATIONAL ACADEMIES SUMMIT ON AMERICAâS ENERGY FUTURE result of increased global economic activity. Twenty percent is due to increased energy intensity in developing nations, which are using more fossil fuels and are using those fuels less efficiently than other countries. And the final 20 percent is accounted for by the troubling observation that sinks responsible for absorb- ing carbon dioxide from the atmosphere appear to be less effective today than they were in the past. For example, changes in wind patterns in the Southern Hemisphere have caused carbon-rich water to stay close to the surface, which means that less carbon dioxide can be absorbed into the oceans. Similarly, the land surface seems to be taking up less carbon dioxide than it has in the past. âThe bottom line is that we are not making progress in reducing carbon dioxide emissions,â said Meserve. âThe problem is getting worse at an accelerating rate over time, rather than better.â THE RELEVANT TIME SCALES Davis and several other speakers at the summit emphasized that issues associated with energy need to be viewed in the context of different time scales. For example, understanding climate change and its implications requires con- sideration of periods of 100 to 200 years. âPolicymakers have never had to take that seriously into account in framing policy,â Davis said. The most important timeframe for policy choices, Davis said, is the period between the present and 25 to 35 years from now. During that time, major components of policy can change, and the dynamics of policy change over that period are somewhat understood. For example, the world will need to go through two major transitions before the middle of the century. Oil produc- tion is likely to enter a long plateau within a decade or two, Davis predicted. Conventional natural gas, about which somewhat less is known, similarly will move toward a plateau before 2050 and maybe earlier, said Davis. The world will have to traverse those two transitions while developing and implementing a new set of technologies for the second half of the century. Over the next 25 to 35 years, the changing geopolitical context and security issues will also have to be taken into account. Major policy initiatives designed to have a substantial impact will require global alliances. âWe need leadership,â Davis said, âand that leadership has to come with the support of people in democracies from the top.â Policies also have to make sense in a highly com- petitive economic framework. Governments will not allow themselves to be left behind if policies damage their industries in the short term. Meeting several immediate requirements can make planning for that period more effective, according to Davis. First, much higher resolution climate mod- els are needed to predict and assess the impacts of climate change in order to weigh the real societal costs and benefits of alternative strategies. For the first time, governments are looking seriously at mitigation and adaptation strate- gies, Davis emphasized. As inputs for this planning, governments need much
THE CHALLENGE OF GLOBAL WARMING 19 more detailed assessments of how climate will and could change and the con- sequences of change. Second, much more analysis is needed regarding technologies expected to be available during the second half of the 21st century. Because relatively little is known now about such technologies, debates over how to reduce emissions by 50 or 80 percent by 2050 are taking place without a proper analytic framework. âWhat does it all look like?â asked Davis. âYou can talk about bits and pieces. We need an integrated assessment of what those pathways are like.â Improving modeling capabilities will contribute to the development of strategies that involve energy technology choices and efforts to develop new technology options. In these efforts, independent advice from groups like the National Academies will be absolutely essential, according to Davis. Assess- ments of energy issues need to be fair, rigorous, and peer reviewed. Conclusions need to be strategically relevant and innovative. They need to generate options, clarify decision making, and ease the process of moving forward. The nexus of energy and the environment poses an extraordinary challenge, said Davis. Responding to this challenge will require a societal transformation that will take place across generations. âThese things never happen in straight lines,â said Davis, âand they require immense courage. Not just of political leaders. That courage can come from anywhere, in any context.â