Liquid Hydrogen: A Mirage or Potent Solution for Aviation's Climate Woes?

The aviation industry faces a formidable challenge to cap its climate impact in the face of continued growth in passengers and freight. Liquid hydrogen (LH2) is one of the alternative jet fuels under consideration as it does not produce carbon dioxide upon combustion. We conducted a well-to-wake life cycle assessment of CO2 emissions and non-CO2 climate change impacts per passenger-distance for 17 different hydrogen production routes, as well as conventional jet fuel and biofuels. Six other environmental and health impact categories were also considered. The Boeing 787-800 was used as the reference aircraft, and a range of flight distances were explored. Contrail cirrus contributes around 81 ± 31% of the combustion climate impacts for LH2, compared to 32 ± 7% for conventional jet fuel, showing that research is needed to reduce uncertainty in the case of LH2. The life cycle impacts of the two dominant commercial LH2 pathways are on average 8 and 121% larger than conventional jet fuel. Some novel LH2 pathways do show considerable potential for life cycle climate impact reductions versus conventional fuel (up to -205 ± 78%). LH2 from renewable energy is not climate neutral, though, at best -67 ± 10% compared to conventional over the life cycle.

Global spatio-temporal change assessment in interregional water stress footprint in China by a high resolution MRIO model.

Developing effective strategies to alleviate increasing water stress in China requires an understanding of how consumption and production drive water stress footprints (WSF) at a high resolution and multiple spatial and temporal scales. However, current Chinese multi-regional input-output (CMRIO) models have limited resolution. Here, we build a high-resolution international MRIO model covering 31 Chinese provinces, 163 sectors, to address this issue, and then analyze the impact of changes in China's interprovincial and international trade patterns on the WSF from 2012 to 2017. We find that China's water stress embodied in inter-provincial trade has increased year after year, to 5606 km3 H2O-eq in 2017, exceeding 50 % of the total domestic footprint. Domestic water stress transfer is most apparent in the outsourcing of water stress from eastern coastal regions to Central and Western regions, with the top interregional supply chain paths mainly associated with the demand of processed rice and tobacco products. China has transformed into a net exporter of water stress in 2017, with water stress exports to developing countries accounting for 54 % of total exports, up from 51 % in 2012. With deepening globalization, trade between China and developing countries has boosted bilateral economic development, while also exacerbating water stress in China. In addition to agricultural cultivation, industrial products such as plastics and steel exported to meet international industries further contribute to water stress in Northern China. Further identify hotspots of water stress consumption is needed to prioritize actions to relieve regional water stress in a more effective manner, and our study can provide key information.

Chilling Prospect: Climate Change Effects of Mismanaged Refrigerants in China.

The global community has responded to the dual threats of ozone depletion and climate change from refrigerant emissions (e.g., chlorofluorocarbons, CFCs, and hydrofluorocarbons, HFCs) in refrigerators and air conditioners (RACs) by agreeing to phase out the production of the most damaging chemicals and replacing them with substitutes. Since these refrigerants are "banked" in products during their service life, they will continue to impact our environment for decades to come if they are released due to mismanagement at the end of life. Addressing such long-term impacts of refrigerants requires a dynamic understanding of the RACs' life cycle, which was largely overlooked in previous studies. Based on field surveys and a dynamic model, we reveal the lingering ozone depletion potential (ODP) and significant global warming potential (GWP) of scrap refrigerants in China, the world's largest producer (62%) and consumer (46%) of RACs in 2015, which comes almost entirely from air conditioners rather than refrigerators. If the use and waste management of RACs continue with the current trend, the total GWP of scrap refrigerants in China will peak by 2025 at a level of 135.2 ± 18.9 Mt CO2e (equal to approximately 1.2% ± 0.2% of China's total greenhouse gas emissions or the national total of either The Netherlands and Czech Republic in 2015). Our results imply an urgent need for improving the recycling and waste management of RACs in China.

Quantifying Domestic Used Electronics Flows using a Combination of Material Flow Methodologies: A US Case Study.

This paper describes the scope, methods, data, and results of a comprehensive quantitative analysis of generation, stock, and collection of used computers and monitors in the United States , specifically desktops, laptops, CRT monitors, and flat panel monitors in the decade leading up to 2010. Generation refers to used electronics coming directly out of use or postuse storage destined for disposal or collection, which encompasses a variety of organizations gathering used electronics for recycling or reuse. Given the lack of actual statistics on flows of used electronics, two separate approaches, the sales obsolescence method (SOM) and the survey scale-up method (SSUM), were used in order to compare the results attained and provide a range for estimated quantities. This study intentionally sought to capture the uncertainty in the estimates. To do so, uncertainty in each data set was incorporated at each stage using Monte Carlo simulations for SOM and establishing scenarios for SSUM. Considering the average results across both methods, we estimate that in 2010 the U.S. generated 130-164 thousand metric tons of used computers and 128-153 thousand tons of used monitors, of which 110-116 thousand tons of used computers and 105-106 thousand tons of used monitors were collected for further reuse, recycling, or export. While each approach has its strengths and weaknesses, both the SOM and the SSUM appear to be capable of producing reasonable ranges of estimates for the generation and collection of used electronics.

Quantifying export flows of used electronics: advanced methods to resolve used goods within trade data.

There is limited convincing quantitative data on the export of used electronics from the United States (U.S.). Thus, we advance a methodology to quantify the export flows of whole units of used electronics from the U.S. using detailed export trade data, and demonstrate the methodology using laptops. Since used electronics are not explicitly identified in export trade data, we hypothesize that exports with a low unit value below a used-new threshold specific to a destination world region are used. The importance of using the most disaggregated trade data set available when resolving used and new goods is illustrated. Two detailed U.S. export trade data sets were combined to arrive at quantities and unit values for each port, mode of transport, month, trade partner country, and trade code. We add rigor to the determination of the used-new threshold by utilizing both the Neighborhood valley-emphasis method (NVEM) and published sales prices. This analysis found that 748 to 1199 thousand units of used laptops were exported from the U.S. in 2010, of which 78-81% are destined for non-OECD countries. Asia was found to be the largest destination of used laptop exports across all used-new threshold methods. Latin American and the Caribbean was the second largest recipient of these exports. North America and Europe also received used laptops from the U.S. Only a small fraction of used laptops was exported to Africa. However, these quantities are lower bound estimates because not all shipments of used laptops may be shipped using the proper laptop trade code. Still, this approach has the potential to give insight into the quantity and destinations of the exports if applied to all used electronics product types across a series of years.