This contribution focuses on the abatement with hydrogen of CO2 and non-CO2 emissions. It is agenda-setting in two respects. Firstly, it challenges the globally accepted hydrocarbon sustainable aviation fuel (SAF) pathway to sustainability and recommends that our industry accelerates along the hydrogen pathway to ‘green’ aviation. Secondly, it reports a philosophical and analytical investigation of appropriate accuracy on abatement strategies for nitrogen oxides and contrails of large hydrogen airliners. For the second contribution, a comparison is made of nitrogen oxide emissions and contrail avoidance options of two hydrogen airliners and a conventional airliner of similar passenger capacity. The hydrogen aircraft are representative of the first and second innovation waves where the main difference is the weight of the hydrogen tanks. Flights of 1000, 2000, 4000 and 8000 nautical miles are explored. Cranfield’s state of the art simulators for propulsion system integration and gas turbine performance (Orion and Turbomatch) were used for this. There are two primary contributions to knowledge. The first is a new set of questions to be asked of SAF and hydrogen decarbonising features. The second is the quantification of the benefits from hydrogen on non-CO2 emissions. For the second generation of long-range hydrogen-fuelled aircraft having gas turbine propulsion, lighter tanks (needing less thrust and lower gas temperatures) are anticipated to reduce NOx emissions by over 20%; in the case of contrails, the preliminary findings indicate that regardless of the fuel, contrails could largely be avoided with fuel-burn penalties of a few per cent. Mitigating action is only needed for a small fraction of flights. For conventional aircraft this penalty results in more CO2, while for hydrogen aircraft the additional emission is water vapour. The conclusion is that our research community should continue to consider hydrogen as the key ‘greening’ option for aviation, notwithstanding the very significant costs of transition.

This paper tests the pollution emissions and institutional quality nexus in Africa. Specifically, we analyze the effect of the political regime and the quality of political governance on CO2 emissions. To control for endogeneity, we apply the system generalized method of moments on a dynamic panel of African countries over the period 1996–2020. The key finding suggests that better institutions have a negative and significant effect on pollution in Africa. The findings also validate the environmental Kuznets curve hypothesis. Moreover, the results support the pollution haven hypothesis. Finally, if digitalization significantly curbs pollution, then industrialization, natural resources, as well as the intensive use of energy, are considered as positive predictors. All the sensitivity and robustness tests globally validate the strength of the negative association between the good quality of institutions and the level of polluting emissions in Africa. The results call for some policy recommendations in environmental regulation for African economies.

Estimates of global and national emissions of carbon dioxide (CO2) are important for scientific understanding and public policy on global climate change. Estimates published annually often see revisions of estimates from previous years. Revisions of data on CO2 emissions reflect revisions of the energy data from which CO2 emissions are estimated. Learning is taking place as missing values are compiled, estimated values are revised, and data management systems are updated. Revisions are a frequent feature of the database. Revisions are widespread among countries, commodities, and transactions. We have examined 11 annual reports of the United Nations Energy Statistics Database (those published from 2010 to 2020) to see in the detailed statistics what values are being changed and what are the magnitudes and patterns of change. They are most common in recent years, among developed countries, and among data on liquid fuels. Revisions are generally small and there are no indications of systematic manipulation or bias. Revisions of specific numbers are believed to represent improvements in accuracy but lack of revisions does not point toward accuracy. This examination of revisions does not permit by itself a quantitative estimate of the data uncertainty but it does suggest that the estimates of global and national totals of CO2 emissions are generally consistent and that both absolute values and trends are reliable over time and sufficiently accurate for scientific understanding and public policy.

The main purpose of this paper is to analyze the contribution of land capital to the growth of emissions and income per capita in the long run. We collect new satellite data from the Earth Observatory to obtain estimates of the Enhanced Vegetation Index at the country level for the period 2000–2015. We use these data and the World Bank wealth estimates of natural capital to calibrate and empirically test an extension of the Green Solow model with land degradation and land capital investment. We show that the model is consistent with the cross-country variation in growth rates of carbon emissions per capita and find that there is convergence at the global level, with the contribution of land capital investment to the growth of emissions being negative and significant in all specifications.

Liquefied natural gas (LNG) offers negligible NOx and SOx emissions as well as reductions in CO2 compared with other liquid hydrocarbons. LNG is a significant player in the global energy mix, with a projection of 40% increase in demand for the next two decades. It is anticipated that the expected rise in demand will cause the fleet of LNG carriers (LNGC) to expand. This work concentrates on steam-powered LNGC, which accounted for 47% of the LNGC fleet in 2018. It performs an empirical analysis of continuous monitoring data that provide high levels of accuracy and transparency. The analysis is done on data collected from 40 LNGCs for over a year to estimate the fleet's operational profile, fuel mix and energy performance. The findings of this work are relevant for bottom-up analysis and simulation models that depend on technical assumptions, but also for emission studies such as the upcoming Fourth International Maritime Organization Greenhouse Gases study.

Les pays en transition ont considérablement réduit leurs émissions de CO2 entre 1995 et 2003. Cette performance est-elle due à l'application d'une politique volontariste de la part des gouvernements, ou bien est-elle un simple effet collatéral de la transformation industrielle majeure subie par ces pays ? Nous tentons de répondre à cette question en développant deux équations structurelles pour la demande (émissions) et l'offre (politique) de pollution. L'équation de l'offre prend en compte la qualité institutionnelle du pays, aussi bien que les préférences des consommateurs pour la qualité de l'environnement. Nos résultats montrent que, toutes choses égales par ailleurs, l'effet d'échelle de la production seul aurait expliqué une augmentation de 31 % des émissions industrielles de CO2 dans les pays en transition entre 1995 et 2003, et l'effet de structure de la production aurait contribué à une augmentation de 8,4 % de ces émissions. Cependant, l'effet technique, qui découle de la sévérité de la politique environnementale, s'est traduit par une réduction de 58 % des émissions industrielles de CO2, et a permis ainsi une réduction nette des émissions industrielles de CO2 de 18 % en 2003 par rapport à 1995. Enfin, notre étude confirme l'importance des facteurs institutionnels dans l'explication des émissions dans les pays en transition.