Экономикалық даму мен теңсіздік арақатынасы: Кузнец қисығы және оның сынлары

Hypothesized relationship between economic development and inequality level

The Kuznets curve ('/k//ʌ//z//n//ɛ//t//s/) expresses a hypothesis advanced by economist Simon Kuznets in the 1950s and 1960s. According to this hypothesis, as an economy develops, market forces first increase and then decrease economic inequality. The Kuznets curve appeared to be consistent with experience at the time it was proposed. However, since the 1970s, inequality has risen in the US and other developed countries, which invalidates the hypothesis.

The Kuznets ratio is a measurement of the ratio of income going to the highest earning households (usually defined by the upper 20%) to income going to the lowest earning households, which is commonly measured by either the lowest 20% or lowest 40% of income. Comparing 20% to 20%, a completely even distribution is expressed as 1; 20% to 40% changes this value to 0.5. Kuznets curve diagrams show an inverted U curve, although variables along the axes are often mixed and matched, with inequality or the Gini coefficient on the Y axis and economic development, time or per capita incomes on the X axis.

In a biography about Simon Kuznets's scientific methods, economist Robert Fogel noted Kuznets's own reservations about the "fragility of the data" which underpinned the hypothesis. Fogel notes that most of Kuznets's paper was devoted to explicating the conflicting factors at play. Fogel emphasized Kuznets's opinion that "even if the data turned out to be valid, they pertained to an extremely limited period of time and to exceptional historical experiences." Fogel noted that despite these "repeated warnings", Kuznets's caveats were overlooked, and the Kuznets curve was "raised to the level of law" by other economists.

Dobson and Ramlogan's research looked to identify the relationship between inequality and trade liberalization. There have been mixed findings with this idea – some developing countries have experienced greater inequality, less inequality, or no difference at all, due to trade liberalization. Because of this, Dobson and Ramlogan suggest that perhaps trade openness can be related to inequality through a Kuznets curve framework. A trade liberalization versus inequality graph measures trade openness along the x axis and inequality along the y axis. Dobson and Ramlogan determine trade openness by the ratio of exports and imports (the total trade) and the average tariff rate; inequality is determined by gross primary school enrolment rates, the share of agriculture in total output, the rate of inflation, and cumulative privatization. various indicators of environmental degradation tend to get worse as modern economic growth occurs until average income reaches a certain point over the course of development. The EKC suggests, in sum, that "the solution to pollution is economic growth." Although subject to continuing debate, there is considerable evidence to support the application of environmental Kuznets curve for various environmental health indicators, such as water, air pollution and ecological footprint which show the inverted U shaped curve as per capita income and/or GDP rise. It has been argued that this trend occurs in the level of many of the environmental pollutants, such as sulfur dioxide, nitrogen oxide, lead, DDT, chlorofluorocarbons, sewage, and other chemicals previously released directly into the air or water. For example, between 1970 and 2006, the United States' inflation adjusted GDP grew by 195%, the number of cars and trucks in the country more than doubled, and the total number of miles driven increased by 178%. However, during that same period certain regulatory changes and technological innovations led to decreases in annual emissions of carbon monoxide from 197 million tons to 89 million, nitrogen oxides emissions from 27 million tons to 19 million, sulfur dioxide emissions from 31 million tons to 15 million, particulate emissions by 80%, and lead emissions by more than 98%. Deforestation may follow a Kuznets curve (cf. forest transition curve). Among countries with a per capita GDP of at least $4,600, net deforestation has ceased. Yet it has been argued that wealthier countries are able to maintain forests along with high consumption by 'exporting' deforestation, leading to continuing deforestation on a worldwide scale.

However, the EKC model is debatable when applied to other pollutants, some natural resource use, and biodiversity conservation. For example, energy, land and resource use (sometimes called the "ecological footprint") may not fall with rising income. While the ratio of energy per real GDP has fallen, total energy use is still rising in most developed countries as are total emission of many greenhouse gases. Additionally, the status of many key "ecosystem services" provided by ecosystems, such as freshwater provision (Perman, et al., 2003), soil fertility, and fisheries, have continued to decline in developed countries. Proponents of the EKC argue that this varied relationship does not necessarily invalidate the hypothesis, but instead that the applicability of the Kuznets curves to various environmental indicators may differ when considering different ecosystems, economics, regulatory schemes, and technologies. At least one critic argues that the US is still struggling to attain the income level necessary to prioritize certain environmental pollutants such as carbon emissions, which have yet to follow the EKC. Yandle et al. argue that the EKC has not been found to apply to carbon because most pollutants create localized problems like lead and sulfur, so there are a greater urgency and response to cleaning up such pollutants. As a country develops, the marginal value of cleaning up such pollutants makes a large direct improvement to the quality of citizens' lives. Conversely, reducing carbon dioxide emissions does not have a dramatic impact at a local level, so the impetus to clean them up is only for the altruistic reason of improving the global environment. This becomes a tragedy of the commons where it is most efficient for everyone to pollute and for no one to clean up, and everyone is worse as a result (Hardin, 1968). Thus, even in a country like the US with a high level of income, carbon emissions are not decreasing in accordance with the EKC. That said, Yandle et al. also concluded that "policies that stimulate growth (trade liberalization, economic restructuring, and price reform) should be good for the environment". Arrow et al. argue pollution income progression of agrarian communities (clean) to industrial economies (pollution intensive) to service economies (cleaner) would appear to be false if pollution increases again at the end due to higher levels of income and consumption of the population at large. A difficulty with this model is that it lacks predictive power because it is highly uncertain how the next phase of economic development will be characterized. Suri and Chapman argue that the EKC is not applicable on the global scale, as a net pollution reduction may not actually be occurring globally. Wealthy nations have a trend of exporting the activities that create the most pollution, like manufacturing of clothing and furniture, to poorer nations that are still in the process of industrial development (Suri and Chapman, 1998). This could mean that as the world's poor nations develop, they will have nowhere to export their pollution. Thus, this progression of environmental clean up occurring in conjunction with economic growth cannot be replicated indefinitely because there may be nowhere to export waste and pollution intensive processes. However, Gene Grossman and Alan B. Krueger, the authors who initially made the correlation between economic growth, environmental clean up, and the Kuznets curve, conclude that there is "no evidence that environmental quality deteriorates steadily with economic growth." In wealthy countries, growth is slower, and pollution reduction efforts can overcome the scale effect. This is the origin of the apparent EKC effect".

Steel production has been shown to follow a Kuznets type curve in the national development cycles of a range of economies, including the United States, Japan, Republic of Korea and China. This discovery, and the first usage of the term "Kuznets Curve for Steel" and "Metal intensity Kuznets Curve" were by Huw McKay in a 2008 working paper (McKay 2008). This was subsequently developed in McKay (2012). A body of work on "Material Kuznets Curves" focused on non ferrous metals has also emerged as academic and policy interest in resource intensity increased during the first two decades of the 21st century.