Final answer:
An altered Earth's axial tilt would change seasonal variations and latitudes of the Tropic of Cancer and Arctic Circle. A decreased tilt would result in less severe seasons and a less pronounced variation in day length. If there were no tilt, traditional seasons would disappear, impacting all aspects of life on Earth.
Step-by-step explanation:
If the Earth's axial tilt were altered, it would lead to significant changes in the Earth's climate and seasons. For example, suppose the axial tilt were changed to 16 degrees. In this scenario, the Tropic of Cancer and Arctic Circle would have different latitudes than they currently do. The Tropic of Cancer, where the sun is directly overhead during the summer solstice, would shift from 23.5° N to correspond with the new 16° tilt. Similarly, the Arctic Circle, defined as the latitude above which the sun does not set on the summer solstice, would move from its current position at 66.5° N latitude to 74° N (90° - 16°).
As for seasonal variations, a decreased axial tilt would lead to less severe seasons. With a tilt of 16°, the contrast between winter and summer temperatures would be reduced, and the variation in day length throughout the year would be less pronounced. Zones of perpetual daylight or darkness at the poles would be narrower. Moreover, if the Earth had no tilt, the seasons as we know them would cease to exist, leading to more uniform temperatures year-round and no significant variation in day length. This would profoundly affect Earth's ecosystems, agriculture, and patterns of human life.