My guess is that you have to think of the dynamics to see that the "jet stream is increasing in speed". Also... you really have to watch how that phrase is even

My guess is that you have to think of the dynamics to see that the "jet stream is increasing in speed". Also... you really have to watch how that phrase is even defined. If the atmosphere were cleanly cut along latitude into "arctic", "mid-latitude" and "tropical" cells then the relative change in temperature would dictate the change in the (static in time) jet stream. So if the arctic warmed faster than mid-latitudes then the temperature gradient and jet activity would decrease. But it's not. Instead, cold air blobs off the poles and we call the wobbles fronts which are associated with jets. Imagine if the number of polar vortex events per year increased from once every four years to 4 per year. Then the overall temperature gradient (and therefore jet activity) could increase even if the poles heated more quickly in the 4 events per year situation. Here, more polar vortex events is a stand in for more overall dynamic activity in the atmosphere.