John W. Day, Louisiana State University
B iophysical constraints will make achieving sustainability for urban areas, especially large ones, challenging in this century. A number of these challenges are already evidenced in several of the cities profiled in Chapter 4. Among the drivers of these challenges are megatrends in population growth and distribution, climate change, energy scarcity, diminished ecosystem services, and requirements of the food system (Day et al., 2014). This appendix briefly addresses each of these in turn.
SETTLEMENT PATTERNS AND POPULATION DISTRIBUTION
The population of the country increased dramatically over the past two centuries and has become increasingly concentrated in urban areas, with urban areas now accounting for roughly 80 percent of the U.S. population (U.S. Census Bureau, 2012). Many see urban living as a “solution” to many of the resource problems facing society. However, global constraints will threaten the sustainability of densely populated regions (UNEP, 2012). Population is now concentrated into a number of large regions (Figure C-1), while areas outside of such megaregions have fallen behind national trends in key measures such as wages and employment over the past three decades. However, these underperforming regions (Figure C-2) are engaged in activities that underwrite the whole economy (farming, forestry, fishing, and mining—especially energy production) and are thus essential for sustaining the rest of the country.
Urbanization of the world’s population is now greater than 50 percent and is projected to continue to increase in the 21st century. This means that population growth is dependent on the fewer and fewer people who work in basic resource industries such as those mentioned above that form the foundation of the economy. For example, less than 2 percent of the population works on farms in the United States (The World Bank, 2016). Supporting an ever-larger population requires the cheap energy and resources that support modern productive agriculture and cheap transportation of products for long distances.
Large urban areas such as those depicted in Figure C-1 use large amounts of resources and energy. In the words of Rees (2012), “Cities are self-organizing far-from-equilibrium dissipative structures whose self-organization is utterly dependent on access to abundant energy and material resources” and are unsustainable in their present form and function (Day et al., 2014, 2016). But human impact now is greater than the regenerative capacity of
1 Note: this section was summarized from Day et al. (2016), supplemented with additional information.
ecosystems to continue to support humanity as measured by ecological footprint analysis (Rees, 2006). Decker et al. (2000) reviewed energy and material flows through the 25 largest urban areas in the world. They concluded that, consistent with Figure C-2, megacities are weakly dependent on the local environment for energy and material inputs, but for water supply and waste sinks largely dependent on the local region. Los Angeles and other cities in the West and Southwest are examples of this. Rees (2012) concluded that if cities are to become sustainable in the future, “they must rebalance production and consumption, abandon growth, and re-localize.” Many cities are now putting forth initiatives particularly in the areas of decentralized, renewable energy systems, lower resource-demanding forms of transportation such as walking and biking, and recycling and engaging in the reduction of water use to address many of these resource deficiencies.
LANDSCAPE PATTERNS OF CLIMATE CHANGE
Global climate change impacts, such as increasing temperatures, sea-level rise, more variable weather, changes in precipitation, and other factors, will challenge sustainability efforts in urban areas of North America in this century (IPCC, 2007; USGCRP, 2009; Walsh et al., 2014). CO2 concentrations in the atmosphere now regularly exceed 400 ppm, a dramatic increase over levels in the late 19th century of 280 ppm (IPCC, 2007). These are the highest CO2 levels of the past three million years. CO2 levels are now tracking at the highest IPCC scenarios (Friedlingstein et al., 2014).
Globally, temperatures increased by nearly 1°C over the last 100 years, and the increase in the Arctic was four to five times higher. Temperatures are projected to increase 1°C to 5°C in this century (IPCC, 2013).
Precipitation is projected to both increase and decrease (IPCC, 2007; USGCRP, 2009), depending on the region. Decreasing precipitation will impact already dry areas in the southern Great Plains and the Southwest, and increases of precipitation in other parts of the United States create a greater risk of flooding (Cook et al., 2015).
Precipitation is predicted to decrease in the Southwest and the lower half of the Great Plains. Cook et al. (2015) reported that climate change will likely increase drought severity in coming decades that will likely exceed the medieval dry period of 1100-1300 CE. Climate in the Southwest is described in a number of books (Ashworth,
Precipitation is projected to increase in the upper Mississippi and Ohio (USGCRP, 2009). There will likely be more extreme weather events with intense precipitation (Min et al., 2011; Pall et al., 2011). Tao et al. (2014a) reported that the combined impacts of climate change and land-use change will lead to increases in peak Mississippi River discharge of 10 to 60 percent by the end of the 21st century.
Because so many metropolitan areas are located on the coast, climate change will strongly impact these areas. Two trends that will affect coastal areas are accelerating sea-level rise and more frequent, stronger hurricanes. Sea level is projected to rise by 1 meter or more in the 21st century (IPCC, 2013; Moser et al., 2012; Pfeffer et al., 2008; Vermeer and Rahmstorf, 2009). The highest estimates are that sea level may rise by 3 meters or more in this century (Hansen et al., 2015).
The number and intensity of hurricanes is related to ocean surface water warming in both the Atlantic and Pacific oceans (Elsner et al., 2008; Emanuel, 2005; Hoyos et al., 2006; Mei et al., 2015; Webster et al., 2005), and projections are that the frequency of the most intense tropical cyclones will increase (Bender et al., 2010; Knutson et al., 2010). Grinsted et al. (2012) reported that hurricane surge was related to warming. Almost all of the costliest Atlantic tropical cyclones occurred since 2000 (Blake et al., 2011). The highest surge for Sandy was nearly 10 meters, and water levels at Battery Park reached nearly 5 meters, the highest ever recorded (NCAR, 2012).
Climate change will likely cause more frequent extreme weather events (IPCC, 2013). Strong precipitation events will occur more often (Min et al., 2011; Pall et al., 2011) and Arctic sea ice melting is related to harsher winters (Greene, 2012; Master, 2014).
In summary, climate change impacts will vary across the landscape. Drought and water scarcity will impact California and the Southwest, and flooding potentially will increase elsewhere. Sea-level rise and more intense tropical cyclones will impact coastal areas. Extreme weather events will become more common across the United States (IPCC, 2013).
ENERGY IMPACTS ON SUSTAINABILITY
Energy is critical to considerations of sustainability, especially in urban areas. First, the consumption of fossil fuels is the primary and most important forcing leading to climate change (IPCC, 2013). Second, energy, and especially fossil fuels, is at the heart of modern society and the industrial economy. Third, energy is at the heart of the globalized industrial food system that is absolutely critical for urban areas, especially large ones. Changes in the cost, availability, and mix of the energy supply system in the 21st century will affect the functioning of modern society and the ability of cities to feed themselves and to continue to import large amounts of energy and other materials. Because fossil fuels are so critical and central to modern society, the focus in this section is mainly on these fuels.
Global energy use is roughly 500 quads per year (quadrillion Btu) and total energy use about doubled from 1973 to 2011. Fossil fuels account for more than 80 percent of world energy use. Other energy sources are less than 15 percent of total energy use. Hydropower, nuclear, and combustible biomass represent most non–fossil fuel use with the “new” renewables (solar, wind, and liquid biofuels) representing about 1 to 2 percent of the total (Smil, 2015).
What is the future of fossil fuel production? One approach that has been commonly used is the Hubbert analysis. M. King Hubbert used an approach (see references at end of the paragraph for a discussion of Hubbert’s approach) based on historical production rates of oil combined with estimates of the ultimate recovery from different fields, for entire regions, and for the world as a whole. Hubbert predicted that U.S. conventional oil production would peak around 1970 and world production would peak during the first decade of the 21st century, both of which have occurred (Aleklett, 2012; Campbell and Laherrère, 1998; Deffeyes, 2001; Hall et al., 2003).
If historical energy consumption patterns are put together with the concept of peak oil and projections for future oil availability, and the availability of energy in general, a disturbing picture emerges. Campbell and Wöstmann (2013) projected world conventional oil and natural gas production peaking between 2020 and 2030 and then declining. Maggio and Cacciola (2012) used a Hubbert analysis to forecast future projections of all three
fossil fuels. They projected that conventional oil production will peak during the second decade of this century, natural gas about 2040, coal just after midcentury, and total fossil fuel production will peak around the same time as natural gas. To replace fossil fuels and nuclear in this century as some suggest, wind and solar would have to grow by nearly two orders of magnitude.
An important issue to consider in any discussion of energy is the net energy yield of any particular energy source. This has been quantified as energy return on investment (EROI), or the ratio between energy outputs to the energy required for production for a particular technology or fuel. Oil and coal had very high EROI up until the mid-20th century: up to 80:1 for coal and 100:1 or greater for oil. The EROI for domestic and imported oil has declined considerably since about 1950. Compared to oil and coal at their highest, the net energy of most other sources of energy have considerably lower EROI values. Hydropower can be as high as 40:1, wind at best can be 20:1 to nearly 40:1, and solar photovoltaics, tar sands, and biofuels are almost always less than 10:1 (Dale et al., 2012; Palmer, 2014; Weißbach et al., 2013). The EROI of liquid biofuels and oil from tar sands is so low as not to represent important viable energy sources for society (Brandt et al., 2013; Hall and Day, 2009; Hall et al., 2014). In spite of the direct economic implications, however, externalities in the form of the environmental costs need to be considered.
Many suggest that renewables, especially wind and solar, will be able to replace fossil fuels in a relatively short period of time. A major problem with solar and wind energy is intermittency. Both solar and wind are intermittent and are often not abundant in areas with the greatest demand (Palmer, 2014; Prieto and Hall, 2013). Winds may be more persistent in coastal areas, but there are higher costs for placing windmills in saltwater and there are high requirements for chromium, zinc, and other elements to make steel less corrosive (Davidsson et al., 2014). Replacing fossil fuels with solar and wind would require enormous amounts of resources, so much so “that the growth of the renewable energy sector may impact investment in other areas of the economy and they stymie economic growth” (Dale et al., 2012). To replace fossil fuels with wind and solar would require very rapid growth rates. Based on the work of Maggio and Cacciola (2012), to increase fossil fuels by a factor of 10 to current levels took 64, 55, and 110 years for oil, natural gas, and coal, respectively. Vaclav Smil (2015) reported that over the past century and a half, it took decades for new energy technologies to become dominant proportions of the energy market. For example, oil took 40 years to grow from 5 to 25 percent of the global primary energy supply, and it will probably require natural gas 60 years to do the same (BP, 2015). Wind and solar increased from about 0.1 percent of total U.S. primary energy consumption in 2000 to about 1 percent in 2010 and 2.2 percent in 2014 (BP, 2015). Even if this rapid rate of growth were to continue, and the materials and manufacturing capacity were not limiting, fossil fuels would still supply 78 percent of U.S. primary energy in 2030, and 75 percent in 2040 (Smil, 2015).
Other renewables that produce electricity include tidal and wave energy, but these produce much less than 1 percent of total world energy use and they are not likely to contribute significantly to future energy use (Dale et al., 2012) beyond very limited geographic circumstances. Biofuels have a very low net energy yield, often hardly greater than 1, and production competes with food production and the preservation of natural ecosystems. Even if all plants on Earth were converted into biofuels, the net energy yield would not supply present world energy demand (Dukes, 2003).
The energy costs of storage (Luo et al., 2015) have not been considered in evaluating renewable EROI of renewables. Replacing fossil fuels with wind and solar would have a huge demand for metals and other resources that would compete with other sectors of the economy (Dale et al., 2012).
Ecosystem services contribute to societal well-being (Costanza et al., 1997; MEA, 2005) and the economy cannot exist without these ecosystem services provided by nature (Costanza et al., 1997). Natural systems, including agroecosystems, are the source of all the energy and materials that form the base of the human economy. This includes agricultural products, fisheries, timber, minerals, and energy (fossil fuels, hydropower, winds, ore for nuclear energy, biomass). Thus sustaining natural ecosystems is absolutely critical to sustain the economy, including that of urban areas (UNEP, 2012). However, degradation of natural systems is leading to a reduction of ecosystem services (MEA, 2005). The Millennium Ecosystem Assessment (MEA) documented pervasive ecosystem
degradation for 15 out of 24 key ecosystems that humans depend on for survival (MEA, 2005; UNEP, 2012). In the United States, ecosystem services are higher in the eastern part of the country due to higher precipitation and rates of primary production. The ecological footprint of society is now more than nature can sustainably support. Because more than 80 percent of the U.S. population lives in urban areas, cities constitute areas of high demand for resources and sinks for waste generation in total, though on a per capita basis cities tend to rank lower than less dense regions (Dodman, 2009; Meyer, 2013). Cities in regions with low levels of ecosystem services, as in the Southwest, will be more at risk as the impacts of climate change and energy scarcity impact society.
AGRICULTURE AND FOOD
Providing adequate food is central to the sustainability of urban areas, especially large ones. The food system that provides food to urban areas covers nearly a billion acres in the United States and is dependent on a globalized industrial agriculture system. In 2007, there were over 922 million acres, 20 percent less than in 1950, about evenly divided between pasture and crops (USDA, 2007). Although there is great amount of U.S. food production, significant amounts of the food consumed in the country are imported. This system is highly energy intensive, much of which in the United States is irrigated, and where crop production is highly variable across the landscape. The great majority of U.S. food production is west of the Mississippi River in areas that are irrigated and where water shortages are projected to grow.
The fertility of U.S. soils is highly variable. Figure C-3 shows the soil fertility index derived by Schaetzl et al. (2012), illustrating the variability in soil quality for plant growth across the nation. Inevitably, utilizing soils for
agriculture causes changes in soil properties and can enhance the risk of erosion (Powlson et al., 2011). The richest soils are in the Midwestern “breadbasket” and the upper Great Plains. The Mississippi Valley and the southern Great Plains also have fertile soils. But much of the east, southwest, and mountain states have low fertility and require soil amendments.
The industrialized agricultural system is highly energy intensive and consumed about 16 percent of U.S. energy used in 2007 (Canning et al., 2010; Hamilton et al., 2013). The total U.S. food system (i.e., farms, transportation, processing, storage, preparation, etc.) consumes more than 7 units of energy to deliver 1 unit of edible food energy (Heller and Keoleian, 2000).
An important consideration for urban sustainability is food. Clearly, cities must have sufficient food, both in quantity and healthfulness, to be sustainable. Prior to the industrial revolution, cities obtained most of their food from their local “foodshed.” Local foodshed refers to food-producing areas inside and within a relatively short distance of the city (e.g., 100 km). With the industrial revolution, agriculture has gone from being local to global, and most food comes from far distances.
Feeding megacities from local production is not feasible. If 100 percent of the current agricultural production of New York State was allocated to New York City, it would meet only 55 percent of the city’s demand (Peters et al., 2009). In regions of high population density, demands among cities for food limits the ability to meet demand from local or regional production. In New England, local production can only meet 16 and 36 percent of the region’s plant- and animal-based food demands, respectively (Griffin et al., 2014). The City of Philadelphia might be able to be fed from a 100-mile radius if the demand of other cities were ignored. However, in the Northeast, regional food demand is far greater than the supply (Kremer and Schreuder, 2012). Low-meat or vegetarian diets can reduce land requirement to less than 30 to 40 percent (Balogh et al., 2011).
Food production from local foodsheds could satisfy the majority of U.S. food demand, including that of most small to mid-sized cities (assuming that current local crop production could be changed to provide a well-rounded diet) (Zumkehr and Campbell, 2015). Sufficient capacity of local or regional production to meet urban or regional demand has been reported in studies for small cities in upstate New York, southeastern Minnesota, and the Midwestern U.S. region (Galzki et al., 2014; Hu et al., 2011; Peters et al., 2009), but not for Willamette Valley in Oregon (Giombolini et al., 2011).
Other factors must be considered in supplying food to cities, such as lower production or crop failure due to climate variability, lack of local production of oils and grains that make up much of dietary calories, competition of food crops with nonedible or export crops, mismatch between local supply and demand, and the costs and resources required for transport (Desjardins et al., 2010; Giombolini et al., 2011). In a larger context, most foodshed analyses do not take into consideration energy and material inputs needed to sustain local food systems, which are often as reliant on nonrenewable energy resources as is agriculture in general. Food production in cities must also deal with contamination problems (Wortman and Lovell, 2013). Finally, significant food production in cities would require that large numbers of city people become farmers!
The trends discussed in this section will affect cities to different degrees. Large cities are especially at risk because of their high demand for energy and resources, and may require innovative ways of obtaining and using those resources more efficiently and effectively. Dense urban cores are functionally integrated with the entire metropolitan areas and likely cannot exist without this larger area. The supply lines that support cities stretch across the globe so that cities are dependent on the globalized economic system that will be impacted by rising energy costs.
The least sustainable region of the United States will likely be the Southwest from the Great Plains to California, primarily because of climate change that will lead to less water for people, agriculture, and natural systems. This region has a high population, especially California, and low levels of ecosystem services. Population in the Southwest is highly concentrated in urban areas, all with uncertain water supplies. Much of the economy of the Southwest is dependent on tourism and discretionary income spending. Coastal areas will be impacted also because of stronger storms and sea-level rise.
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