Seasons differ in the northern and southern hemispheres because the earth is not upright on its axis in relation to the sun.
Instead, the earth is tilted at about 23.5° from the vertical position relative to the sun.
The earth revolves around the sun over the course of a year.
When the earth’s Southern Hemisphere is tilted toward the sun, the rays of the sun hit that part of the earth more directly and cause warmer temperatures, resulting in summer weather.
At the same time, the Northern Hemisphere is tilted away from the sun, so it receives fewer direct rays of the sun and experiences winter weather.
Because the earth tilts on its axis as it travels around the sun, only half the planet faces the sun directly at any one time.
Thus, in July, when the Northern Hemisphere faces the sun, North America has summer weather, while South America is experiencing winter.