One reason for this is that China’s urban planners have discouraged its megacities from growing too large in population size. This implied Zipf’s law distribution is taken holding the 95th percentile city’s size and rank fixed. Note: Population is measured in 10,000 people. Source: World Bank calculations using CEAD emissions data for 175 cities in 2010 and population density data from Liu et al. If Zipf’s law held, China’s megacities would have far higher populationsĬurrent population size and rank, current vs. If Guangzhou had the same density as Seoul, for example, it could accommodate 4.2 million more people. ![]() Zipf’s law is a special case that tends not to hold in reality, but even a more moderate rank-size rule would imply substantially more populous megacities. Indeed, if Zipf’s law held, Beijing and Shanghai would be respectively three and four times more populous. Nonetheless, China’s megacities remain significantly less populous and less dense than one might expect, and its mid-size cities are much larger (Figure 2). Since the mid-1990s, as migration to the coastal areas increased, China’s largest coastal cities started to grow rapidly, restoring a more natural pattern of urbanization. After the 1960s it diverged substantially, as industries and industrial centers were relocated from the coast to the interior under the Third Front Movement. In the early 19th century, China’s city size distribution closely followed the rank-size rule. Benchmarking China’s city size distribution against Zipf’s law reveals how government policy has shaped China’s urbanization in ways that may run counter to economic forces. ![]() Of course, this empirical regularity serves mainly illustrative purposes. The special case in which the estimated power equals –1 is known as Zipf’s law, named after a linguist, George Zipf. That is, the rank r associated with a city of size S is proportional to S to some negative power. An anomalous city-size distributionĪ striking pattern that has long fascinated both urban scientists and economists is that the distribution of city population size and rank in many countries seems to closely follow the rank-size rule. This does not augur well for efficiency or emissions. Meanwhile, Chinese cities have been expanding outward: China is the only country in East Asia to have declining population density in its large cities, as the expansion of urban boundaries has outpaced population inflows. In recent years, such controls have been lifted in smaller cities but tightened in megacities. China has traditionally controlled rural-urban migration through the hukou household registration system. In the past few years, many of China’s megacities, such as Beijing and Shanghai, have made plans to cap the size of their populations. For China’s economy and its emission intensity, it matters where these people move to. Assuming an urbanization rate of 70 percent by 2030, some 80 million people may move to urban areas over the next decade alone. This finding is important because China is still urbanizing. CO2 emissions per capita are measured in 100 tons per person. Note: Population density is measured in 10,000 people per square kilometer. Source: World Bank calculations using CEAD emissions data for 175 prefecture-level and above cities in 2010 and population density data from Liu et al. Log of CO2 emissions per capita and log of population density for 175 Chinese cities ![]() Population density of Chinese cities is negatively correlated with per capita emissions ![]() As illustrated in Figure 1, there is a statistically significant negative relationship between population density and per capita emissions, even after controlling for income, economic structure, and proxies for environmental policy. Researchers at Australian National University have found that this is true also for China. The recent World Bank Commodity Markets Outlook shows that urban density tends to lower energy consumption intensity from transport, infrastructure, and accommodation. However, beyond a certain level of per capita income, as people move into denser urban spaces, their carbon footprint declines. In many developing countries, urbanization is often associated with higher carbon emissions, resulting from rising consumption levels and associated energy needs. Twitter KathAStapleton Denser Chinese cities have lower per capita emissions
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