Explore the vast range of titles available.

China's clean air policies have successfully mitigated fossil fuel CO.sub.2 (CO.sub.2ff or C.sub.ff) emissions in bottom-up inventories since 2013. Yet, evidence from top-down measurements and their underlying drivers remains limited. Here, we quantify C.sub.ff concentrations and fuel-specific contributions using atmospheric Î(.sup.14 CO.sub.2) and [delta](.sup.13 CO.sub.2) measurements across representative Chinese cities. We found regional differences in C.sub.ff and co-emission characteristics: megacities like Guangzhou show an indicative inter-period decrease in wintertime C.sub.ff concentrations, of roughly 56 %-64 % lower in 2022 than in 2010 in afternoon-equivalent terms, while smaller cities have yet to demonstrate comparable decreases. These changes are consistent with a 23 % reduction in coal use, a 17 % increase in the natural-gas contribution (evidenced by stable isotope analysis), and improved combustion efficiency (indicated by a 63 % decline in RCO/CO2ff ratios). Notably, the 24 years observational record (1998-2022) shows steeper declines in urban RCO/CO2ff ratios than inventory estimates, suggesting current emission inventories may underestimate combustion efficiency improvements and CO emission reductions relative to C.sub.ff mitigations. These findings are consistent with progress toward mitigating C.sub.ff and co-emitted CO in major Chinese cities. They also underscore how coal-to-gas transitions and technological upgrades simultaneously advance air quality and climate goals. Importantly, our results highlight the critical need to integrate top-down observational frameworks (e.g. radiocarbon measurements) with traditional inventories to better capture rapid, policy-driven emission changes and inform future co-benefit optimization strategies.

Tough choices loom if the world wants to go green. The United States and other countries must decide where and how to procure the materials that make our renewable energy economy possible. To build electric vehicles, solar panels, cell phones, and millions of other devices means the world must dig more mines to extract lithium, copper, cobalt, rare earths, and nickel. But mines are deeply unpopular, even as they have a role to play in fighting climate change. These tensions have sparked a worldwide reckoning over the sourcing of these critical minerals, and no one understands the complexities of these issues better than Ernest Scheyder, whose exclusive access has allowed him to report from the front lines on the key players in this global battle to power our future.

The book is about much more than a mere list of uses of the energy minerals, which are the most important concerns of one and all now-a-days. In this book, all the eight energy minerals have been brought within one cover. The book traces the history of use of each mineral to its beginning in India, as well as in the other parts of the world; it explains the reasons why a particular grade of a particular mineral is used for a particular purpose.

We present a new method for partitioning observed CO.sub.2 enhancements (CO.sub.2 xs) into fossil and biospheric fractions (C.sub.ff and C.sub.bio) based on measurements of CO and [delta].sup.13 CO.sub.2, complemented by flask-based Î.sup.14 CO.sub.2 measurements. This method additionally partitions the fossil fraction into natural gas and petroleum fractions (when coal combustion is insignificant). Although here we apply the method only to discrete flask air measurements, the advantage of this method (CO- and [delta].sup.13 CO.sub.2 -based method) is that CO.sub.2 xs partitioning can be applied at high frequency when continuous measurements of CO and [delta].sup.13 CO.sub.2 are available. High-frequency partitioning of CO.sub.2 xs into C.sub.ff and C.sub.bio has already been demonstrated using continuous measurements of CO (CO-based method) and Î.sup.14 CO.sub.2 measurements from flask air samples. We find that the uncertainty in C.sub.ff estimated from the CO- and [delta].sup.13 CO.sub.2 -based method averages 3.2 ppm (23 % of the mean C.sub.ff of 14.2 ppm estimated directly from Î.sup.14 CO.sub.2 ), which is significantly less than the CO-based method which has an average uncertainty of 4.8 ppm (34 % of the mean C.sub.ff). Using measurements of CO, [delta].sup.13 CO.sub.2 and Î.sup.14 CO.sub.2 from flask air samples at three sites in the greater Los Angeles (LA) region, we find large contributions of biogenic sources that vary by season. On a monthly average, the biogenic signal accounts for -14 to +25 % of CO.sub.2 xs with larger and positive contributions in winter and smaller and negative contributions in summer due to net respiration and net photosynthesis, respectively. Partitioning C.sub.ff into petroleum and natural gas combustion fractions reveals that the largest contribution of natural gas combustion generally occurs in summer, which is likely related to increased electricity generation in LA power plants for air-conditioning.

Radiocarbon (.sup.14 CO.sub.2) observations are the benchmark for quantifying fossil fuel CO.sub.2 (ffCO.sub.2) in the atmosphere, but continuous .sup.14 CO.sub.2 measurements are not yet available. Continuous estimates of ffCO.sub.2 can be made by observing continuously measurable proxies that are co-emitted during fossil fuel combustion. This paper investigates the potential and challenges of using in situ NO.sub.x observations in urban areas to quantitatively estimate hourly ffCO.sub.2 enhancements, in the example of the ICOS pilot station in Heidelberg, Germany. The short atmospheric lifetime of NO.sub.x limits the use of the observed signal to a local area. Thus, a local NO.sub.x and ffCO.sub.2 background was approximated using the Stochastic Time-Inverted Lagrangian Transport (STILT) model and bottom-up emission estimates from the Netherlands Organisation for Applied Scientific Research (TNO). Using .sup.14 CO.sub.2 data from 185 hourly integrated flask samples between 2020-2021, mean ratios of local excess NO.sub.x (ÎNO.sub.x) to local excess ffCO.sub.2 (ÎffCO.sub.2) of 1.40 ppb ppm.sup.-1 for winter and 2.12 ppb ppm.sup.-1 for summer were calculated. These ratios were applied to the ÎNO.sub.x time series to construct continuous ÎffCO.sub.2 estimates. The uncertainty of the ÎNO.sub.x -based ÎffCO.sub.2 record was estimated at 3.94 ppm. Comparisons with .sup.14 CO.sub.2 -based and ÎCO-based ÎffCO.sub.2 estimates showed good agreement, while still demonstrating distinct behaviour for individual events. ÎNO.sub.x shows considerable potential as ÎffCO.sub.2 proxy and as useful addition to ÎCO-based estimates, as both proxies have different footprints due to their lifetimes. A key challenge remains in reliably determining the seasonal and diurnal cycle of average ÎNO.sub.x to ÎffCO.sub.2 ratios.

A relaxed eddy accumulation (REA) system was developed and tested, enabling conditional sampling of air for subsequent .sup.14 CO.sub.2 analysis. This allows a .sup.14 C-based estimation of fossil fuel CO.sub.2 concentrations in the collected air samples and, thus, an observation-based partitioning of total CO.sub.2 fluxes measured in urban environments by eddy covariance into fossil and non-fossil components. This article describes the REA system, evaluates its performance, and assesses uncertainties in the concentration measurements. In the REA system, two separate inlet lines equipped with fast-response valves and loop systems adapted to the technical requirements enable the conditional collection of air in two sets of aluminum cylinders for updraft and downdraft samples, respectively. The switching between updraft sampling, downdraft sampling, and standby mode is thereby determined by the vertical wind measured at 20 Hz by a co-located ultrasonic 3D anemometer. A logger program provides different options for the definition of a deadband, which is used to increase the concentration differences between updraft and downdraft samples. After the sampling interval, the accumulated air is transferred by an automated 24-port flask sampler into 3 L glass flasks, which can be analyzed in the laboratory, and the cylinders are re-evacuated for the next sampling. The REA system was tested in the laboratory, as well as on a tall tower near the city center of Zurich, Switzerland. Between July 2022 and April 2023, 103 REA updraft and downdraft flask pairs for flux measurements and 9 flask pairs for quality control purposes were selected from the tall tower for laboratory analysis based on suitable micro-meteorological conditions. Uncertainties in the CO.sub.2 concentration differences between updraft and downdraft flasks were estimated by simulations using 20 Hz in situ measurements of a closed-path gas analyzer and an open-path gas analyzer co-located with the ultrasonic anemometer. The measurements show that there is no significant bias in the concentration differences between updraft and downdraft samples and that uncertainties due to the sampling process are negligible when estimating fossil fuel CO.sub.2 signals. In the Zurich measurements, the CO.sub.2 concentration differences between the flask pairs agreed with the differences obtained from in situ measurements within -0.005 ± 0.227 ppm. The largest source of uncertainty, as well as the main limitation, in the separation of fossil and non-fossil CO.sub.2 signals in Zurich was the small signal-to-noise ratio of the Î.sup.14 C differences measured by accelerator mass spectrometry between the updraft and downdraft flasks. The novel REA flask sampling system meets the high technical requirements of the REA method and is a promising technology for observation-based estimation of fossil fuel CO.sub.2 fluxes.

This paper questions the extent to which the introduction of utility-scale, privately generated renewable energy into South Africa's coal-dominated electricity supply can be considered a 'low-carbon transition'. Rather, the renewable energy projects in question are embedded within and contribute to South Africa's high-carbon, electricity-intensive 'minerals-energy complex'. An empirical consideration is provided of some of the stakeholders involved in the implementation of the wind industry in South Africa, and the possibilities and pitfalls for its long-term sustainability.

Accurate estimation of fossil fuel CO.sub.2 (ffCO.sub.2) emissions is essential for climate prediction and the development of mitigation policies. Top-down carbon-nitrogen joint observations offer the potential for more reliable ffCO.sub.2 estimates. Here, we establish an inversion framework for urban ffCO.sub.2 emissions based on combined active-passive satellite observations. Urban ffCO.sub.2 distributions were first constructed using satellite NO.sub.2 data and CO.sub.2 -NO.sub.x emission ratios, and monthly ffCO.sub.2 emissions for selected global cities were then estimated by integrating the total column dry-air carbon dioxide (XCO.sub.2) from the DQ-1 ACDL instrument. Our results show that satellite-derived NO.sub.x emissions provide strong constraints on urban anthropogenic CO.sub.2 estimates. Validation against TCCON ground-based observations indicates that, compared with conventional top-down inversion approaches, our method more accurately reproduces urban ffXCO.sub.2 plume distributions. We further evaluated the influence of different CO.sub.2 -NO.sub.x ratio calculation methods on ffCO.sub.2 estimates and found variations exceeding 150, exerting a substantial impact on emission inversions. Under observational constraints, the uncertainty in CO.sub.2 -NO.sub.x ratios derived from different methods decreased by 9.79 %-38.78 %, and the variation range was reduced by more than 100 %, converging toward a consistent magnitude. This study advances understanding of the spatiotemporal patterns of urban ffCO.sub.2 emissions and provides a unified perspective for future CO.sub.2 -NO.sub.x -based anthropogenic carbon emission estimation.

The COVID-19 pandemic and Russia’s war on Ukraine have impacted the global economy, including the energy sector. The pandemic caused drastic fluctuations in energy demand, oil price shocks, disruptions in energy supply chains, and hampered energy investments, while the war left the world with energy price hikes and energy security challenges. The long-term impacts of these crises on low-carbon energy transitions and mitigation of climate change are still uncertain but are slowly emerging. This paper analyzes the impacts throughout the energy system, including upstream fuel supply, renewable energy investments, demand for energy services, and implications for energy equity, by reviewing recent studies and consulting experts in the field. We find that both crises initially appeared as opportunities for low-carbon energy transitions: the pandemic by showing the extent of lifestyle and behavioral change in a short period and the role of science-based policy advice, and the war by highlighting the need for greater energy diversification and reliance on local, renewable energy sources. However, the early evidence suggests that policymaking worldwide is focused on short-term, seemingly quicker solutions, such as supporting the incumbent energy industry in the post-pandemic era to save the economy and looking for new fossil fuel supply routes for enhancing energy security following the war. As such, the fossil fuel industry may emerge even stronger after these energy crises creating new lock-ins. This implies that the public sentiment against dependency on fossil fuels may end as a lost opportunity to translate into actions toward climate-friendly energy transitions, without ambitious plans for phasing out such fuels altogether. We propose policy recommendations to overcome these challenges toward achieving resilient and sustainable energy systems, mostly driven by energy services.