Since the late 1970s China has moved from a closed, centrally planned system to a more market-oriented one that plays a major global role - in 2010 China became the world's largest exporter. Reforms began with the phasing out of collectivized agriculture, and expanded to include the gradual liberalization of prices, fiscal decentralization, increased autonomy for state enterprises, creation of a diversified banking system, development of stock markets, rapid growth of the private sector, and opening to foreign trade and investment. China has implemented reforms in a gradualist fashion. In recent years, China has renewed its support for state-owned enterprises in sectors it considers important to "economic security," explicitly looking to foster globally competitive national champions. After keeping its currency tightly linked to the US dollar for years, in July 2005 China revalued its currency by 2.1% against the US dollar and moved to an exchange rate system that references a basket of currencies. From mid 2005 to late 2008 cumulative appreciation of the renminbi against the US dollar was more than 20%, but the exchange rate remained virtually pegged to the dollar from the onset of the global financial crisis until June 2010, when Beijing allowed resumption of a gradual appreciation. The restructuring of the economy and resulting efficiency gains have contributed to a more than tenfold increase in GDP since 1978. Measured on a purchasing power parity (PPP) basis that adjusts for price differences, China in 2010 stood as the second-largest economy in the world after the US, having surpassed Japan in 2001. The dollar values of China's agricultural and industrial output each exceed those of the US; China is second to the US in the value of services it produces. Still, per capita income is below the world average. The Chinese government faces numerous economic challenges, including: (a) reducing its high domestic savings rate and correspondingly low domestic demand; (b) sustaining adequate job growth for tens of millions of migrants and new entrants to the work force; (c) reducing corruption and other economic crimes; and (d) containing environmental damage and social strife related to the economy's rapid transformation. Economic development has progressed further in coastal provinces than in the interior, and approximately 200 million rural laborers and their dependents have relocated to urban areas to find work. One consequence of the "one child" policy is that China is now one of the most rapidly aging countries in the world. Deterioration in the environment - notably air pollution, soil erosion, and the steady fall of the water table, especially in the north - is another long-term problem. China continues to lose arable land because of erosion and economic development. The Chinese government is seeking to add energy production capacity from sources other than coal and oil, focusing on nuclear and alternative energy development. In 2009, the global economic downturn reduced foreign demand for Chinese exports for the first time in many years, but China rebounded quickly, outperforming all other major economies in 2010 with GDP growth around 10%. The economy appears set to remain on a strong growth trajectory in 2011, lending credibility to the stimulus policies the regime rolled out during the global financial crisis. The government vows, in the 12th Five-Year Plan adopted in March 2011, to continue reforming the economy and emphasizes the need to increase domestic consumption in order to make the economy less dependent on exports for GDP growth in the future. However, China likely will make only marginal progress toward these rebalancing goals in 2011. Two economic problems China currently faces are inflation - which, late in 2010, surpassed the government's target of 3% - and local government debt, which swelled as a result of stimulus policies, and is largely off-the-books and potentially low-quality.