Aviation Impacts on Fuel Efficiency of a Future More Viscous Atmosphere

Aircraft cruising near the tropopause currently benefit from the highest thermal efficiency and the least viscous (sticky) air, within the lowest 50 km of Earth's atmosphere. Both advantages wane in a warming climate, because atmospheric dynamic viscosity increases with temperature, in synergy with the simultaneous engine efficiency reduction. Here, skin friction drag, the dominant term for extra aviation fuel consumption in a future warming climate, is quantified by 34 climate models under a strong emissions scenario. Since 1950, the viscosity increase at cruising altitudes (similar to 200 hPa) reaches similar to 1.5% century(-1), corresponding to a total drag increment of similar to 0.22% century(-1) for commercial aircraft. Meridional gradients and regional disparities exist, with low to midlatitudes experiencing greater increases in skin friction drag. The North Atlantic corridor (NAC) is moderately affected, but its high traffic volume generates additional fuel cost of similar to 3.8 x 10(7) gallons annually by 2100, compared to 2010. Globally, a normal year after 2100 would consume an extra similar to 4 x 10(6) barrels per year. Intermodel spread is <5% of the ensemble mean, due to high inter-climate model consensus for warming trends at cruising altitudes in the tropics and subtropics. Because temperature is a well-simulated parameter in the IPCC archive, with only a moderate intermodel spread, the conclusions drawn here are statistically robust. Notably, additional fuel costs are likely from the increased vertical shear and related turbulence at NAC cruising altitudes. Increased flight log availability is required to confirm this apparent increasing turbulence trend.