Transport makes up around 20 percent of our energy use around the world—and that figure is set to grow, according to the International Energy Agency. With sustainable solutions in mind, a new study published by eminent physicist Jo Hermans in MRS Energy and Sustainability—A Review Journal (MRS E&S) looks at the energy efficiency of current modes of transport—from bicycles to buses, from air transport to cruise ships— and concludes that liquid hydrogen seems to be a realistic option for what is probably the most problematic of transportation modes in terms of sustainability, future air travel.