The tilt of the Earth. The farther you are away from the sun you are the less heat or the cooler the temperature will be or vise versa. The closer you are to the sun the warmer the temperature will be.
There has not been a data study as of this time to figure out the average temperature of North America. This maybe due to the fact that yearly the temperatures can change drastically as well as during seasons.
it stays the same as energy is added. or The temperature of a substance does not change during a phase change, until the change is complete. Ideally, during phase change the temperature is stable until the change is complete. Though pressure has to be kept constant.