The deployment of low-emission alternative fuels is crucial to decarbonise the transport sector. A number of alternatives like hydrogen or dimethyl ether/methanol synthesised using CO₂ as feedstock for fuel production (hereafter refer to “CO₂-based fuels”) have been proposed to combat climate change. However, the decarbonisation potential of CO₂-based fuels is under debate because CO₂ is re-emitted to the atmosphere when the fuel is combusted; and the majority of hydrogen still relies on fossil resources, which makes its prospects of being a low-carbon fuel dependent on its manufacturing process. First, this paper investigates the relative economic and environmental performance of hydrogen (produced from conventional steam methane reforming and produced via electrolysis using renewable energy), and CO₂-based fuels (dimethyl ether and methanol), considering the full carbon cycle. The results reveal that hydrogen produced from steam methane reforming is the most economical option and that hydrogen produced via electrolysis using renewables has the best environmental profile. Whereas the idea of CO₂-based fuels has recently gained much interest, it has for the foreseeable future rather limited practical relevance since there is no favourable combination of cost and environmental performance. This will only change in the long run and requires that CO₂ is of non-fossil origin, i.e. from biomass combustion or captured from air. Second, this paper address unresolved methodological issues in the assessment of CO₂-based fuels, such as the possible allocation of emissions to the different sectors involved. The outcomes indicate that implementing different allocation approaches substantially influences the carbon footprint of CO₂-based fuels. To avoid allocation issues, expanding the boundaries including the entire system and is therefore recommended.

Intracranial volume reflects the maximally attained brain size during development, and remains stable with loss of tissue in late life. It is highly heritable, but the underlying genes remain largely undetermined. In a genome-wide association study of 32,438 adults, we discovered five previously unknown loci for intracranial volume and confirmed two known signals. Four of the loci were also associated with adult human stature, but these remained associated with intracranial volume after adjusting for height. We found a high genetic correlation with child head circumference (genetic = 0.748), which indicates a similar genetic background and allowed us to identify four additional loci through meta-analysis (N combined = 37,345). Variants for intracranial volume were also related to childhood and adult cognitive function, and Parkinson's disease, and were enriched near genes involved in growth pathways, including PI3K-AKT signaling. These findings identify the biological underpinnings of intracranial volume and their link to physiological and pathological traits.