Construction of Fully Substituted Cyclobutanes by Tandem Reaction of 1,4-Diyn-3-ols and Anhydrides.

A concise and efficient synthesis of fully substituted cyclobutane derivatives from 1,4-diyn-3-ols and anhydrides was developed. Mechanistic studies indicated that a tandem esterification, isomerization to give allenyl ester, and homointermolecular [2+2] cycloaddition might be involved. The features of this protocol are its operational practicality, mild reaction conditions, and high regio- and stereoselectivity, and it is a readily accessible gram-scale synthesis.

Global simulation of fine resolution land use/cover change and estimation of aboveground biomass carbon under the shared socioeconomic pathways.

Land use change driven by human activities plays a critical role in the terrestrial carbon budget through habitat loss and vegetation change. Despite the projections of the global population and economic growth under the framework of the Shared Socioeconomic Pathways (SSPs), little is known of land use/cover change (LUCC) at a fine spatial resolution and how carbon pools respond to LUCC under different SSPs. This study projected the future global LUCC with 1 km spatial resolution and a 10-year time step from 2010 to 2100 and then explored its direct impacts on aboveground biomass carbon (AGB) under SSPs. Scenario SSP3 yields the highest global cropland expansion, among which approximately 48% and 46% is expected to be located in the current forest land and grassland, respectively. Scenario SSP1 has the largest forest expansion and is mainly converted from grassland (54%) and cropland (30%). Due to the spatial change in land use/cover, global AGB loss is expected to reach approximately 3.422 Pg C in 2100 under scenario SSP3 and increases by approximately 0.587 Pg C under scenario SSP1. Africa is expected to lose 30% of AGB under the scenario SSP3. Aboveground biomass in Asia will fix 0.774 Pg C to reverse the AGB loss in 2100 under scenario SSP1. The global carbon loss estimated by the land use products with 10 km and 25 km resolution are less than that with 1 km by 1.5% (ranging from -11.2% in Africa to +34.0% in Oceania) and 2.9% (ranging from -11.8% in Africa to +24.0% in Oceania), respectively. These findings suggest that sufficient spatial details in the existing SSP scenario projections could reduce the uncertainties of AGB assessment, and reasonable land use development and management is a key measure to mitigate the negative impacts of LUCC on the biomass carbon pool.

Investigating the impacts of three-dimensional spatial structures on CO2 emissions at the urban scale.

In response to carbon dioxide (CO2) emissions, numerous studies have investigated the link between CO2 emissions and urban structures, and pursued low-carbon development from the standpoint of urban spatial planning. However, most of previous efforts only focused on urban structures in term of two-dimensional space, whereas the vertical influence of urban buildings (three-dimensional space) plays an important role in CO2 emissions. To address this issue, we took the cities in mainland China as study case to quantitatively explore how the three-dimensional urban structure affects CO2 emissions. First, we collected the city-level CO2 emission data from a greenhouse gas emission dataset released by the China City Greenhouse Gas Working Group. Then, a series of spatial metrics were established to quantify three-dimensional urban structures based on urban building data derived from Baidu Map. On the strength of the Stochastic Impacts by Regression on Population, Affluence, and Technology (STIRPAT) model, an extended approach and ridge regression analysis were finally utilized to investigate the consequences of three-dimensional urban structures on CO2 emissions at the city level. The results indicate that the total building volume is the largest driving force accelerating CO2 emissions due to the massive consumption of energies for human activities during rapid urbanization. Besides, urban buildings with taller height and large heat dissipation area also have significant positive effects on promoting CO2 emissions. Although a compact coverage of urban buildings at a two-dimensional scale contributes to the reduction of CO2 emissions, urban structure characterized by an intense and congested pattern in three-dimensional space can lead to more CO2 emissions because of the adverse impacts from surrounding environment and traffic congestion. Additionally, an irregular pattern of three-dimensional urban structure would help reduce CO2 emissions to some extent. Such study results highlight the importance of urban planning for the development of a low-carbon city, and suggest the compact patterns of three-dimensional urban structures should be controlled within a reasonable range to avoid more CO2 emissions caused by excessive centralization and aggregation.

Projecting China's future water footprint under the shared socio-economic pathways.

Increasing water scarcity in China is further exacerbated by the rapid socio-economic development and uneven spatial distribution of water resources. Current studies on water footprint have mainly focused on historical accounting and trend analysis at the provincial scale. However, a comprehensive exploration of future water footprint would be vital to a better understanding of future water shortage challenges, and more importantly, would allow the mitigation of water scarcity and inequal water distribution. In this paper, we present an approach to project the future water footprint of China at a fine resolution (0.125 arc-degree) under the shared socio-economic pathway (SSP) scenario framework, which described five future alternative socio-economic development pathways over the 21st century. We first simulated the future spatial patterns of built-up land using the Future Land Use Simulation (FLUS) model and derived the future population growth and urbanization rate from the population projection provided by the National Center for Atmospheric Research (NCAR). Then future water footprint was projected according a log-transformed linear regression calibrated with historical data during 2007-2012. We found that the total volume of China's water footprint will increase significantly in the future under the SSP1, SSP4 and SSP5 scenarios, reaching up to nearly 400 billion m3 in 2050, equivalent to almost 40% increase compared to that in 2010. The spatial patterns of future water footprint show dramatic increase (up to 100-130%) in the eastern provinces (Shandong, Henan, and Hebei), and slight decrease were found in the western provinces (Xinjiang, Ningxia, and Qinghai). In addition, the future water footprints were found to share very similar spatial patterns at local pixel scale among different SSP scenarios in three of the largest metropolitan areas of China (Beijing-Hebei-Tianjin, Yangtze River Delta, and Pearl River Delta). These findings provide extensive knowledge of the future water footprint and suggest a more severe water scarcity in the future from a consumption-oriented perspective. More effective water management policies are urgently needed to mitigate future water resource scarcity and inequality.

Global projections of future urban land expansion under shared socioeconomic pathways.

Despite its small land coverage, urban land and its expansion have exhibited profound impacts on global environments. Here, we present the scenario projections of global urban land expansion under the framework of the shared socioeconomic pathways (SSPs). Our projections feature a fine spatial resolution of 1 km to preserve spatial details. The projections reveal that although global urban land continues to expand rapidly before the 2040s, China and many other Asian countries are expected to encounter substantial pressure from urban population decline after the 2050s. Approximately 50-63% of the newly expanded urban land is expected to occur on current croplands. Global crop production will decline by approximately 1-4%, corresponding to the annual food needs for a certain crop of 122-1389 million people. These findings stress the importance of governing urban land development as a key measure to mitigate its negative impacts on food production.