system
Given the following post, respond as if you're commenting on Reddit:
human
If the earth was to stop rotating around its axes; how cold would the dark side get ?

and how would the weather patterns change?
gpt
Planets that "have stopped rotating" are known as being tidally locked.  Earth's moon is tidally locked to the Earth, and so only one side faces us at all times.  If a planet is close enough to its parent star it will become tidally locked.  Observation of exoplanets determined to be tidally locked indicated extreme winds between day and night sides. 

HD 189733 b is a roughly Jupiter sized exoplanet which exhibits this phenomenon.  A temperature range of 973 ± 33 K to 1,212 ± 11 K was discovered, indicating that the absorbed energy from the parent star is distributed fairly evenly through the planet's atmosphere.  Assuming the planet is tidally locked, this suggests that powerful easterly winds moving at more than 9,600 kilometers per hour are responsible for redistributing the heat.

If something similar were to happen on Earth, we would all die very quickly.  All crops and plants would quickly succumb to temperature variations of hundred of degrees Kelvin, the winds would rip out the largest trees.  The entire ecosystem would most likely be destroyed.  Significant quantities of water would boil into the atmosphere.  If the heated atmosphere from the day side were incapable of keeping the night side warmed,  theoretically the boiled off oceans could be transported to the night side where the water would be deposited and frozen.

edit: We wouldn't *all* die, the crew of the ISS would be quite comfortable until their return to Earth.