If the earth was tilted, there would be small changes in temperature, but there will be no seasons. The Earth's axis is now inclined at around 24 degrees. This is the main reason for the changing of the seasons. The Northern Hemisphere is in the warm season when the Earth is slanted toward the sun, and the Northern Hemisphere is in the cold season when the Earth is slanted away from the sun. The cycle repeats itself every year because the Earth rotates around the sun at a known and generally constant rate. The sun is higher in the sky during the warm season, making it warmer, and lower in the sky during the cool season, making it colder.
