Cities and climate change interlinkages manifest themselves in several forms. For a long time, the focus of such interactions in climate policy debate has been one-sided, i.e. the impact of cities on climate through emissions of energy-related greenhouse gases. This did not provide a complete picture, especially since climate change has been scientifically confirmed as already occurring: cities are increasingly affected by the physical impact of climatic change such as the heightened frequency of adverse climate effects - flooding, hurricanes, infrastructure damage, etc. - and the socio-economic impacts of such consequences. In addition to the implications of impacts of physical climatic changes, cities will be increasingly affected economically, socially and environmentally, though indirectly, due to the requirements of international climate regimes, increasingly low emission technologies, growing carbon markets, technology transfers, and financial mechanisms. Such interactions are shown in Fig. 7.1.
From a natural science perspective, cities affect climate through changes in a number of other parameters in addition to emissions but these are largely not considered in most of the literature dealing with urban climate change issues. However, this is not surprising
* Cities affect emissions through fossil energy use and land use changes
Fig. 7.1. Cause/impact interactions between cities and climate change.
* Cities affect emissions through fossil energy use and land use changes
Fig. 7.1. Cause/impact interactions between cities and climate change.
as such studies at urban levels are largely led by scholars from the energy-environment field. In reality, changes in urban vegetation can affect the amount of carbon sequestration by a large city. Of all organic carbon pools in cities, perhaps trees are the most intensively studied because of their links to other concerns such as urban heat island, air pollution and urban aesthetics. McPherson et al. (2005a-c) show that in six US cities - Fort Collins, Berkeley, Boulder, Bismarck, Cheyenne and Minneapolis - the amount of carbon dioxide absorbed by each city tree - whether in streets or parks - is in the range of 79 to 107 kg annually. Urban trees not only sequester carbon but also lower the cooling burden of air conditioners and thus reduce emission of CO2 related to electricity production (Akbari 2002; Taha 1997; Dhakal 2002). The heat discharged by air conditioning equipment is a significant outcome of urban energy use in many cities. In Tokyo, studies show that such urban energy uses are responsible for a maximum of about 3.4°C changes in temperature in downtown Tokyo on a typical summer day (Dhakal and Hanaki 2002; Ichinose et al. 1999). Apart from explaining cities' links to climate change through emissions and sequestrations, radiative forcing-based examinations of such linkages are generally ignored. Cities - and urbanization in general - boost the emission of aerosols, and alter the carbon balance in soil, evaporation, moisture and albedo value (the degree of surface reflectivity) that affect radiative forcing. Cities critically influence the dynamics of climate change through many such factors outside the realm of greenhouse gas emissions. Although important, these are largely ignored.
However, cities are often identified as sources of climate change problems in broader terms. Fossil fuels are reported to supply 80.3% of global commercial energy (IEA 2006) and a large share of this is used to support urban areas. In OECD countries, cities consume between 70 to 80% of fossil fuel nationally (OECD 1995). Svirejeva-Hopkins et al. (2004) mention that 'although the total area of urbanised territories is relatively small (2% of the global land area in the 1990s) (Grubler 1994), they play a more important role in the carbon cycle because these territories emit up to 97% of all anthropogenic carbon emissions (Grubler 1994) and urbanised territories transform the structure of the local carbon flows over considerably larger areas than what they occupy'. We doubt such high share of emissions by urbanized territories but regardless of the accuracy of such ambitious number, it highlights the key role that cities play through their emissions. We should raise the subsequent question then: are rural areas doing any better? In the developing world, which has a low level of urbanization and a small fraction of people living in cities, the per capita end-use of energy is perhaps higher than in rural areas. Previous studies have already established that income has a strong correlation with energy intensive lifestyles up to a certain level. Thus, pertaining to large income gaps between urban and rural areas, it seems reasonable that cities are responsible for higher end-use and embodied energy use per capita than rural areas. Additionally, fossil energy availability in cities is usually better and thus supply problems do not limit the use of commercial energy, as is more common in rural areas. End-use energy consumption in many rural areas is indeed supply constrained, and often does not involve a 'modern', i.e. fossil or nuclear, form of energy. Being dominated by traditional sources, the end-use efficiency of energy use in rural households is expected to be low and therefore it is unlikely that per capita primary energy use in rural household surpasses urban for that reason. So we accept here that per capita energy use and carbon emissions in rural households are lower because these units tend to use traditional energy sources that largely come from renewable energy sources - biomass -unless they cause deforestation, releasing greenhouse gas and affecting carbon sinks. Since urbanization is rapidly increasing in the developing world, the contribution of cities to the emission of greenhouse gases will further increase due to the greater demands of energy despite continuously improving technologies.
In the developed world, the per capita incomes in urban and peri-urban areas are already higher and energy cost makes a smaller fraction of total disposable income compared to the developing countries. It does not make income elasticity of energy demand as significant a factor as in the developing world. As income plays a lesser role in energy use, population density effect becomes more important. As a result, per capita energy use in cities might be smaller than suburban and other peri-urban areas due to the fact that economy of scale persists in cities due to efficient production and distribution systems, and that people in cities live in smaller houses, commute less by private car, and use public transport more than in rural areas. It is generally accepted that a denser city consumes less energy per capita and thus emits less carbon than a sprawled city if other conditions remain unchanged. However, the extent of density difference matters too because the definition of 'dense' in Asian cities is often different from sprawled North American cities. When it comes to rural areas, a study in Japan shows that per capita total energy use in rural areas is more than in urban areas (e.g. Ichinose et al. 1993), primarily due to excessive automobile dependence in rural areas. However, there are arguments that if we consider total energy use, people in cities opt for more services and consume more, similar to those in cities in developing countries. Lenzen et al. showed in 1997 that in Australia urban total energy use was higher than in rural or country areas - simply due to higher total consumption, including that of energy.
In the year 2005, about half of the world's population, or about 3.2 billion people out of 6.5 billion people on earth, lived in urban areas, and urbanization rates, particularly in developing countries of Asia and Africa, are rising rapidly.1 Projections show that urban populations will grow twice as fast as compared to the total population resulting in 4.9 billion people living in urban areas by 2030. This is about 60% of the projected world population of 8.2 billion. That means that 1.8 billion people will be added to urban populations in the next 25 years, of which 1.1 billion alone will be added to Asia (UN, 2006). Such an urban expansion would mean an enormous increase in energy demand due to rapidly rising per capita energy use, brought about by industrialization and rising urban incomes
1 World urbanization rate is projected to reach 50% by 2008. Asia hosts the largest urban population of 1.6 billion, Europe 0.5 billion, Africa 0.3 billion, North America 0.3 billion, and others 0.4 billion. China, India and the USA have the largest urban populations as countries (UN 2006).
and consumption, and increases in the urban population itself. It is very likely that all gains in technological efficiency will be overshadowed by the very scale of energy use in cities. This puts an enormous pressure on efforts to control greenhouse gas emissions through the introduction of renewable power sources, while preserving the local environment and natural carbon sinks. As mentioned earlier, urban areas already consume large amount of global commercial energy and are therefore likely to be responsible for a comparable share in fossil fuel-related CO2 emissions. Studies show that cities embody considerable amounts of energy in their buildings and infrastructure, as well as carbon emissions due to the flows of goods and services that are consumed in the city. A large city's actual carbon responsibilities are hence much higher than they appear from accounts of direct energy use or direct carbon emissions, say from electricity use or transport. Urban areas are among the most significant systems to be considered when developing a human world that is low in carbon dioxide emissions. This does not mean that we should or indeed can turn away from cities. Historically, cities have played a crucial role in human modernization, industrialization, innovation, and technology development, and urban communities are key to finding solutions to a variety of human problems. They should be viewed as places that offer great economic and socio-cultural opportunities to mitigate emissions. The denser settlement in cities provides a great opportunity to create an efficient production and distribution infrastructure, make public transportation feasible, and encourage people to use efficient technology in addition to allowing the conservation of energy relating to shelters, lifestyle, mobility and other key human needs (Lebel et al. 2007).
Urban greenhouse gas emissions are generated by three kinds of activities. The first type of activity produces direct emissions within the physical boundary of the city. Coal burnt in boilers in the city, natural gas burnt in homes, gasoline or diesel combusted by vehicles are only a few of such examples for direct emission sources. Such emissions generally result from the use of fossil forms of energy sources such as coal, gas, oil - but not electricity -and activities from non-energy sectors in the city such as methane emanating from urban rice plantations, or the collection, transfer, treatment or combustion of solid waste, and other activities. The second activity type, producing indirect emissions, encompasses those types of energy use in the city where energy is used inside a city with the actual emissions taking place outside its boundaries. Most electricity generation, in particular, still involves primary energy sources such as coal, oil or gas being burnt outside a city's boundaries. In addition, emissions from energy are often accounted for from the perspective of end-use without considering the energy lost in transportation and conversion, or from the primary energy supply side after accounting all such losses in the long chain of energy production, conversion and distribution. In practice, such direct and indirect emissions are well accepted in policy discussions, policy design, and policy instruments in many cities. However, the question of how to evaluate the responsibility of a particular city and for what we should make the city accountable remains to be answered. Cities have ecological 'footprints' that are many times their size - meaning that the city survives due to goods and services, in both the physical and ecosystem sense, from outside of the city - and a large waste stream requires massive ecological space to be absorbed. Similarly, a large volume of emissions takes place outside of the city to produce the goods and services consumed by the city dwellers, and large areas of forest and oceans are relied on as emission sinks. The question of how to account for this third type of activity when estimating greenhouse gas emissions is unresolved and has not yet reached the point of being widely acknowledged or resolved in policy discussions, let alone international agreements. If we consider such embodied emissions, the per capita emission of greenhouse gases allocated to a city will likely increase significantly; it can increase several times if the city is big and well developed but resource-scarce with a predominance of service and commercial activities (Kaneko et al. 2003). Whether embodied emissions will be considered in any future policy response in cities is a different matter and a complicated one, but consideration of such factors would help to advance cities towards societal development that is not as focused on the overconsumption of materials, which in itself has multiple benefits. In addition, this concept would aid in moving towards the development of the so-called Sound Material-Recycle Society that the Japanese government has been touting of late, enhance the concept of a Circular Economy in China,2 and assist in the conservation of natural resources and friendly material substitution policies in Europe (MOEJ 2006b; Yuan et al. 2006).
Cities are also victims of climate change and environmental problems. Historically cities have played a key role in the world's industrialization and faced air and water pollution and other environmental adversities. Through the heat island effect the heat balance in cities is altered, contributing to heat stress, increasing trends of rising smog and poor visibility, raising ozone levels and lowered life expectancy - and growing energy bills for greater cooling demands (Dhakal 2002). Coastal cities face flooding and hurricane problems and their infrastructures are increasingly being compromised in their capacity to protect urban dwellers. For example, the capital of Bangladesh, Dhaka, which is very prone to drainage congestion, periodic flooding and hurricanes, is 2 to 13 metres above sea level with the majority of urban areas only 6 to 8 metres above sea level (Alam and Rabbani 2007). The 1988 flood in Dhaka inundated 85% of the city. In the greater Cape Town area, water demand exceeds total potential yield (Mukheibir and Ziervogel 2007). The downtown part of the city of Mumbai sits on a flood-prone and poorly drained area. The devastating flood of July 2005 in Mumbai that killed more than 1000 urban dwellers was triggered by 944 millimetres of rainfall in a 24-hour period (Sherbinin et al. 2007). In Shanghai, severe flooding of the Yangtze River in August 1998 caused 3000 deaths and displaced 16 million people with a total damage estimate of US$36 billion (cited from several sources by Sherbinin et al. 2007). In the New York Metropolitan Region, many coastal communities have been identified as being at high risk of sea-level rises and storm surges that affect both affluent as well as low income communities (Gornitz and Couch 2000). Poor, inner city communities are seriously affected by summer heatwaves due to the prevalence of high risk populations such as the elderly poor (Kinney et al. 2001). Hurricane Katrina's impacts on New Orleans in the United States in 2005 is a reminder to us that cities are prone to natural disasters irrespective of whether they are located in developed or developing parts of the world and thus future climatic changes are going to increase the burden and exacerbate these already pressing problems in cities.
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