| Urban, despite its samll area coverage on the earth, is an important driving force of global carbon cycle. Carbon balance and management in urban regions form one of the top topics in global carbon studies. With the support of the National Nature Science Foundation, this study develops a research framework for urban carbon source and sink study. Taking Shanghai as an example, this study discusses the variations of carbon source and sink and the driving mechanisms, carbon emission in Shanghai is also predicted for 2020, by integrating field survey, social-economic data collection and analysis, GIS methods. This study provides not only theorical research framework and methodologies for urban carbon source/sink study, but also scientific basis for urban carbon management. The main conclusions can be summed up as follows.(1) Carbon emission due to energy consumption ("carbon emissions" for short hereinafter) increased from 28.77 to 51.64 million tons during the period of 1994 to 2006 in Shanghai, about 3.5% of China's carbon emissions (2005 data). Carbon intensity was declining from 2.51 tons / ten thousands in 1994 to 1.07 tons / ten thousands in 2006 (GDP's constant prices of 1990), average annual decline rate 5.3%, but only 2.6% since 2001. Shanghai's carbon emission intensity was about 69% of the national average, but bigger compared to developed countries with higher energy efficiency, which 46%,27% and 30% more than Britain, Germany and Japan respectively.(2) The energy structure was optimized because of using more clean electricity and natural gas, but compared to developed countries, the proportion of low-carbon energy was lower in Shanghai. The share of electricity was more and more big in terminal energy consumption, and it's mainly from thermal electricity which has higher carbon emission coefficient than other fossil fuels, so it's essential to develop clean electricity. The carbon emissions of second industry were largest, but the proportion was gradually declining in total carbon emissions from 80% in 1994 to 62% in 2006. The carbon emissions of tertiary industry were growing fastest because of the development of the transport industry, which consumed more oils, and the proportion was 29% of total carbon emissions in 2006. Carbon emission intensity of tertiary industry was lower than second industry, so industrial structure adjustment led to a general decline in carbon intensity. However, the proportion of secondary industry output has increased after 2002, which made a slower rate of carbon emission intensity in Shanghai.(3) Over 60% of carbon emissions was from industry in Shanghai. Industrial output growth topped other factors to be the most important driving force for carbon emission increase, while energy intensity decline, energy structure and industrial structure adjustment were factors to mitigate carbon emissions. Of them, Energy intensity contributed 90% industrial carbon emissions decrease, which declined from 0.61 t SCE / ten thousands in 1996 to 0.16 t SCE / ten thousands in 2007. The impact of the energy mix varies from industry to industry, and the rising share of electricity led to carbon emissions increase in many sectors.80% industrial output come from heavy industry in Shanghai, and 89% of industrial carbon emissions from heavy industry. In particular, five biggest sectors in heavy industry (i.e. ferrous metal smelting and rolling processing industry, raw chemical materials and chemical products industry, petroleum and nuclear fuel processing and coking industry, nonmetals minerals mining and dressing industry, and production and supply of electric power, steam hot water industry) contributed to 85% of total carbon emissions from heavy industry, while their output share was only less than 30%. So, industrial structure adjustment was the main approach to reduce industrial carbon emissions.(4) With the increase of population in Shanghai, transport carbon emissions of residents traveling became an important source of carbon emissions increase. Four kinds of vehicles, private car, bus, taxi and metro were selected, and found that their carbon emissions showed a rising trend. In 2006 carbon emissions from residents traveling reached 1.35 million tons,71% more than that in 2002. Rapidly growing of private cars was the main reason, and its carbon emissions was equal to the sum of the other three kinds in 2006, and the proportion varied form 22% in 2002 to 48% in 2006. The per capita carbon emissions of metro was 0.013 kg C/ person, buses 0.12 kg C/ person, and taxi 0.31 kg C/ person.(5) Carbon sinks of terrestrial ecosystems in Shanghai were 296 thousand tons in 2003, of which vegetation accounted for 85%, and the remaining 15% green spaces soil, however agricultural soil had no significant effect. The analysis showed that carbon sinks were only 0.7% of carbon emissions of the year, so the offset effect of terrestrial ecosystems carbon sinks to carbon source can be negligible.(6) From the aspect of age of forest, most was young forest, natural and normal growth permitted, there would be great potential for carbon storage.(7) Paddy soil play a minor role in carbon sequestration, but paddy area reduced quickly, while paddy soil transformed to vegetable soil, urban land as well as forest land, which resulted in decreasing of soil organic carbon, and soil showed as carbon source. After afforestation of farmland, soil organic carbon declined in the short term. Mostly forest land was used to provide sapling for city landscaping in Shanghai, with a short forest rotation, while soil organic carbon could not be accumulated, so there was no carbon sink in forest soil which distributed in the farmland.(8) Speaking of green spaces soil itself, carbon sink of 0 - 30cm layer was 44868 tons / year,1.84 tons / ha·year per unit area. But on the whole process of urbanization, green spaces soil carbon pool can not offset the decrease due to urbanization. Although the green coverage was growing, the soil carbon pool was still losing due to urbanization.(9) According to carbon emission reduction targets proposed by China, the United States, the European Union and Japan in the Copenhagen conference on climate change, the carbon emissions of Shanghai in 2020 was projected, which was 73.86,39.86,39.38 and 37.22 million tons respectively, and carbon emission intensity decreased by 45%,70%,71%,72%compared to the year of 2005, per capita carbon emissions were 2.99,1.61,1.59 and 1.51 t C / person. If maintaining the level of carbon emissions of 2005 in 2020, then the carbon emissions intensity of Shanghai would fall 64%.(10) According to China's emission reduction target, if achieved, per capita living consumption of carbon emissions of Shanghai in 2020 would be 0.25 t C / person, amount 6.175 million tons, accounting for 8.4% of the total, slightly higher than that in 2005. The carbon emissions intensity of primary industry would be 1.07 t C / million, accounting for 0.5% of the total carbon emissions. Carbon emission intensity in secondary and tertiary industry would decline 45% and 20% respectively, then their output proportion be 21.7%,78%. If Japan's emission reduction target realized, social development and life consumption patterns must be changed tremendously, per capita living consumption would be 0.16 t C/ person. Assumed only having tertiary industry its carbon emission intensity should descend at least 55% to achieve the target. Or the carbon intensity of tertiary industry and secondary industry fell 60%,75%, while the ratio of output 27:73, then the target could also be achieved.
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