It’s a heat engine but more than just temperature changes are occurring.
“The new study, by University of Chicago Professor Tiffany Shaw and NSF NCAR scientist Osamu Miyawaki, uses climate models to show that climate change intensifies this density contrast because moisture levels for air above the tropics will increase more than above the poles.”
I guess it's like someone putting water on the coals in a sauna and the people feel a huge wave of heat due to the increased heat transfer, even though they've literally cooled down the coals.
I also think some of the confusion is coming from the use of the term 'weakening'. It is true that the primary jetstream wind pattern is weakening relative to it's stabler state.
That weakening means the jetstream meanders more, with more latitudinal movement in its form.
The strength overall of the jetstream wind is weaker when it's meandering, but can also be much more intense in places.
This says nothing about humidity or energy or pressure, just windspeed and direction.
“The new study, by University of Chicago Professor Tiffany Shaw and NSF NCAR scientist Osamu Miyawaki, uses climate models to show that climate change intensifies this density contrast because moisture levels for air above the tropics will increase more than above the poles.”
https://news.ucar.edu/132935/jet-stream-winds-will-accelerat....