The purpose of this paper is to describe global urban greenhouse gas emissions by region and sector, examine the distribution of emissions through the urban-to-rural gradient, and identify covariates of emission levels for our baseline year, 2000. We use multiple existing spatial databases to identify urban extent, greenhouse gas emissions (CO 2 , N 2 O, CH 4 and SF 6) and covariates of emissions in a "top-down" analysis. The results indicate that urban activities are significant sources of total greenhouse gas emissions (36.8 and 48.6 % of total). The urban energy sector accounts for between 41.5 and 66.3 % of total energy emissions. Significant differences exist in the urban share of greenhouse gas emissions between developed and developing countries as well as among source sectors for geographic regions. The 50 largest urban emitting areas account for 38.8 % of all urban greenhouse gas emissions. We find that greenhouse gas emissions are significantly associated with population size, density, growth rates, and per capita income. Finally, comparison of our results to "bottom-up" estimates suggest that this research's data and techniques are best used at the regional and global scales. 1 Introduction Decision makers need baseline data, analysis and monitoring of urban greenhouse gas emissions to verify the effectiveness of policy measures. For example, while urban planners take

Continuous no-till (NT) has numerous benefits, including improved soil aggregate stability in the surface soil and increased rate of water infiltration, but accumulation of soil P at the soil surface with NT can increase P concentration in runoff. We hypothesized that occasional one-time tillage of NT land, conducted once in 10 or more years, can reduce P runoff and improve crop yields without reducing soil aggregation or increasing runoff. Research was conducted in long-term NT fields under rainfed corn [Zea mays (L.)] or sorghum [Sorghum bicolor (L.) Moench.] rotated with soybeans [Glycine max (L.)Merr.] at two locations in eastern Nebraska. Tillage treatments were applied in the spring or fall and included continuous NT, tandem disk (disk), chisel with 10-cm-wide twisted shanks, moldboard plow (MP), and mini-moldboard plow (miniMP). Subplots had either 0 or 87.4 kg P ha 21 applied as composted feedlot manure before tillage. Yield and yield components were measured for 2 and 3 yr after the spring and fall one-time tillage, respectively. In Year 2 or 3 after tillage, soil sorptivity, field-saturated infiltration rate, runoff volume, runoff P loss, and soil aggregate stability were determined. Yield was not affected by the tillage 3 compost interaction, but was increased by compost application at one location and sorghum yield was affected by tillage treatments at the second location. Grain yield was never significantly more or less with one-time tillage as compared with NT. Soil aggregate stability was not affected by tillage treatments. Sorptivity and infiltration were increased with MP tillage compared with NT at one location but reduced at the other. One-time MP tillage reduced dissolved P loss at both locations and total phosphorus (TP) loss at one location. The benefit of one-time MP tillage in terms of reduced dissolved reactive P loss in runoff was positive with no negative effect on soil aggregate stability but no gain in yield.

Stratification of nutrient availability, especially of P, that develops with continuous no-till (NT) can affect runoff nutrient concentration and possibly nutrient uptake. The effects of composted manure application and one-time tillage of NT on the distribution of soil chemical properties, root colonization by arbuscular mycorrhizae (AM), and plant P uptake were determined. Research was conducted on Typic Argiudoll and Mollic Hapludalf soils under rainfed corn (Zea mays L.) Abbreviations: AM, arbuscular mycorrhizae; ARDC, Agricultural Research and Development Center of the University of Nebraska-Lincoln; CH20 and CH30, chisel tillage at the 20-and 30-cm depths; FAME, ester-linked fatty acid methyl ester; MMP, mini-moldboard plow; MP, moldboard plow; NT, continuous no-till; R6, stage of physiological maturity for corn and sorghum or full enlargement of soybean seed; RMF, Rogers Memorial Farm of the University of Nebraska-Lincoln; TP, total phosphorus; V6, six-leaf growth stage.

Policymakers need clear, consistent, and reliable information about the location of greenhouse gases and drivers of emitting activity in order to design appropriate mitigating strategies. At the urban scale, there have been challenges in developing consistent and reliable emissions inventories. This chapter examines selected methods to determine greenhouse gas emissions at the urban scale. We describe the various criteria considered when constructing an urban greenhouse gas protocol including the definition of urban, the gasses that are measured, the source they come from, the scope of analysis and how the measurements are undertaken. We then present results for European medium and large sized cities derived from alternative methodologies to demonstrate the range of results. Finally, we briefly discuss the policy implications of the various approaches.

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