what would happen if the axis of the earth was not tilted

If the Earth's axis were not tilted, the planet would experience no seasons as currently known. The Sun would be directly overhead at the equator year-round, and the length of day and night would remain constant everywhere, roughly 12 hours each. Without the axial tilt, temperature variations would be much more extreme between the equator and the poles—equatorial regions would be intensely hot continuously, while polar regions would remain in a state of perpetual cold with little sunlight, resembling eternal winter or dusk. This lack of seasonal variation would drastically impact global climate and ecosystems. Weather patterns would be far less variable with less variation in temperature and precipitation throughout the year. The polar regions would have consistently cold and dark conditions, and the famous cycles of wet and dry or warm and cold seasons seen in many parts of the world would be replaced by more uniform weather conditions year-round. Additionally, the absence of tilt might intensify wind systems due to stronger temperature gradients between equator and poles. Overall, such a scenario would mean no traditional seasons, very different climate zones, and a likely significant disruption of ecosystems and life cycles dependent on seasonal changes.