We don't know as much as we think we do.
The jet stream is a dastardly complex creature, and figuring out what makes it tick has challenged atmospheric scientists since it was discovered about 75 years ago.
So we've only known of the existence of a jet stream for three-quarters of a century - figuratively speaking, the blink of an eye.
We know that Vikings farmed on Greenland for a couple of hundred years, until advancing ice pushed them out. Now the ice is retreating (except where it's increasing, like Antarctica), and this is due to human activity (supposedly). Yet we've only been studying that big yellow ball in the sky for a few decades:
Unknown until SOHO, solar orbiting satellites, is that the Sun has a total energy output that has only varied by 1% during the 30 year data collection period, hence the 'solar constant'. What is not constant is solar particle output, which increases during sunspot activity and these particles cause variation in Earth's internal fission rate, creating a binary climate driving system. Due to the atmosphere and ocean influence, this is a binary system is self buffering. Earth's elliptical orbit causes a 3% variation in Earth-Sun distance, a 10% variation in solar input.
But the sun has little influence upon planetary climate; that changes because of human activity. The fact that we're in a period of extremely low sunspot activity is irrelevant. We must be forced to spend more in order to consume less so that government can Save The Planet™.
It would actually be nice if Mann-made global warming was in fact a reality, as it would enable us to grow more food. As the Vikings observed in Greenland, cold is a killer.