The tropics are the region surrounding the equator where the Sun can shine directly overhead, bounded by the Tropic of Cancer (23.4°N) and the Tropic of Capricorn (23.4°S), which mirror Earth's axial tilt. Because the Sun remains high in the sky all year, this zone receives the most solar energy, resulting in the planet's highest temperatures and lowest seasonal variation—seasons are defined by precipitation (wet/dry) rather than temperature. The region hosts a remarkable diversity of climates, including rain forests, monsoons, savannahs, deserts, and high-altitude snow-capped mountains, and the term "tropical" can also describe specific weather patterns. Covering roughly 39.8% of Earth's surface and 36% of its landmass, the tropics housed 40% of the global population in 2014, a share projected to reach 50% by 2050. Global warming is causing tropical weather conditions to expand into the subtropics, leading to more extreme events like heatwaves and intense storms, which could render some areas uninhabitable. The name "tropic" derives from the Greek tropē ("to turn"), and the boundaries were historically named after the constellations Cancer and Capricorn, though the Sun's overhead position has since shifted due to the precession of the equinoxes.