Umair Irfan in Vox:
Aviation produces about 2.5 percent of global carbon dioxide emissions. If you add in the heat-trapping effects of water vapor in contrails and other pollutants, air travel accounts for about 4 percent of the warming across the planet induced by humans to date. It may seem like a small slice of the climate change problem, but if left unchecked, aviation’s carbon dioxide emissions are poised to double by 2050. “The biggest problem is that demand is rising,” said Gökçin Çınar, an assistant professor of aerospace engineering at the University of Michigan. Even as aircraft grow more fuel-efficient per passenger, more flyers will lead to more greenhouse gases.
However, decarbonizing aircraft is a huge technical challenge. To get a 400,000-pound airliner off the ground, up to 35,000 feet, and across an ocean, you need to squeeze an enormous amount of energy into a tiny space at the lowest weight possible. This trait is called specific energy, which is measured in watt-hours per kilogram or megajoules per kilogram. The best lithium-ion batteries top out around 300 watt-hours per kilogram. Jet fuel has a specific energy around 12,000 watt-hours per kilogram. And as an airplane burns fuel, it gets lighter, increasing its efficiency and range, whereas a dead battery weighs just as much as a live one. Swapping a gasoline engine for an electric motor in a car is trivial in comparison.
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