Evidence for Large Increases in Clear-Air Turbulence Over the Past Four Decades

Abstract

Clear-air turbulence (CAT) is hazardous to aircraft and is projected to intensify in response to future climate change. However, our understanding of past CAT trends is currently limited, being derived largely from outdated reanalysis data. Here we analyze CAT trends globally during 1979–2020 in a modern reanalysis data set using 21 diagnostics. We find clear evidence of large increases around the midlatitudes at aircraft cruising altitudes. For example, at an average point over the North Atlantic, the total annual duration of light-or-greater CAT increased by 17% from 466.5 hr in 1979 to 546.8 hr in 2020, with even larger relative changes for moderate-or greater CAT (increasing by 37% from 70.0 to 96.1 hr) and severe-or-greater CAT (increasing by 55% from 17.7 to 27.4 hr). Similar increases are also found over the continental USA. Our study represents the best evidence yet that CAT has increased over the past four decades.