Northern Hemisphere Jet Stream Waviness Has Been Governed by Natural Variability Since 1979

As global climate change progresses, especially with the warming poles, the behaviour of the Northern Hemisphere jet-stream remains a key factor in predicting mid-latitude weather patterns. This study assesses whether the jet-stream has become wavier from 1979 to 2023 using daily 500 hPa geopotential height data. By analysing ERA5 reanalysis and state-of-the-art climate models, we isolate the effects of natural variability and CO2 forcing on jet-stream dynamics across four sub-regions of the Northern Hemisphere: Eurasia, North Atlantic, North America, and North Pacific. Contrary to some recent hypotheses, our findings reveal no significant increase in jet-stream waviness over the study period. While there are some seasonal variations, natural variability remains the primary driver of jet-stream behaviour, with limited influence from rising CO2 concentrations, particularly in spring and summer. These results contribute to ongoing discussions about the roles of natural variability and anthropogenic forcing in the past and/or future evolution of jet-stream dynamics.