Abstract: Climate change has increasingly influenced human life and CO₂ emissions has become a major factor causing global climate warming. China is one of top CO₂ emissions nations and has drawn the world attention. China commit CO₂ emissions will arrive peak around 2030, which means that China will gradually turn from the energy intensity and CO₂ emissions intensity control into the total energy consumption and CO₂ emissions control and finally realize the economic growth and CO₂ emissions"decoupling". At the same time, Chinese urbanization is interwoven with CO₂ emissions. Cities has played agglomeration effect with population and land consolidation, but it also accelerated factors of high concentration by energy consumption, such as population, economic and transportation. Therefore, cities become a leading platform to reduce CO₂ emissions in a region or a country. On the other hand, the western region has priority in the national regional development strategy through the west development program and its CO₂ emissions also get rapid growth. Current research is mainly focused on eastern and central megalopolis, the research conclusion is not fit for the unique path, measures and strategies of low carbon development in western megalopolis. Xi'an City, the only international metropolis in northwest China, lies in the core area of Guanzhong-Tianshui Economic Zone and is a new starting point in Silk Road Economic Belt. Taking Xi'an City as example, with the statistical data of GDP, energy consumption and population of Xi'an from 2005 to 2014, this paper analyzed the CO₂ emissions change trend and the low carbon city's development prospect till year 2030 in different scenarios using scenario analysis and decoupling theory. The study found that CO₂ emissions continued to grow and there was decoupling relationship between CO₂ emissions and economic growth in recent years. The carbon productivity kept rising and CO₂ emissions per capita was under the domestic advanced level. Compared with inertial scenario, the CO₂ emissions will be reduced by nearly 50% before 2030 in decoupling scenario, and the scenario can be achieved actively with green and low carbon transition. An important breakthrough in traffic and architect was found that the growth rate of CO₂ emissions from industrial enterprises above designated size had declined, but private cars and public buildings kept a stable rising trend. There were many positive factors and potential to energy conservation and emissions reduction in these key areas. Based on these results, this paper shows"high carbon"in the economic development with all kinds of features, such as difference of resources endowment, lock-in effect of energy consumption structure, the energy inefficiency, unreasonable urban spatial structure, high energy public buildings and weak carbon sink. Finally, we put forward new proposals such as industrial technical reconstruction, reasonable urban spatial layout, the promotion of green building and innovation of social governance, etc.

Key words: low carbon development, status, strategy, metropolis, Xi'an City