Climatologists classify the world into five major climate zones using the Köppen system: tropical (A), dry (B), temperate (C), continental (D), and polar (E). Tropical climates feature high temperatures year-round, with every monthly average above 18°C, and significant rainfall that supports rainforests and savannas. Dry or arid climates occur where evaporation exceeds precipitation, producing deserts and semi-arid steppes with sparse vegetation. Within the temperate category, a Mediterranean climate stands out for its dry, hot summers and mild, wet winters, found in places like southern Europe and California.
A key contrast exists between continental and oceanic climates. Continental climates experience larger temperature extremes between seasons because land heats and cools faster than water, leading to hot summers and cold winters inland. Oceanic climates, moderated by nearby seas, have milder seasonal swings. Several factors influence which climate a region experiences: latitude (which determines how much solar energy arrives), altitude (higher elevations are cooler), proximity to oceans, ocean currents, prevailing winds, and topography such as mountain ranges that block or redirect moisture.
The ultimate cause of seasons is the tilt of Earth's axis at 23.5° relative to its orbital plane. As Earth orbits the Sun, this tilt causes different hemispheres to receive varying amounts of solar radiation throughout the year, producing spring, summer, autumn, and winter. Combined with the geographic factors listed above, axial tilt sets the stage for the remarkable diversity of climates observed across the planet.