Northern Hemisphere

The Northern Hemisphere is the half of Earth that lies north of the Equator. Its surface is 60.7% water, a lower proportion than the Southern Hemisphere, and it contains 67.3% of the planet's landmass. This land includes all of North America and mainland Eurasia, about two-thirds of Africa, and a small portion of South America. The hemisphere’s climate is shaped by Earth’s axial tilt of 23.439281°, which creates seasonal variations in day length and temperature, with temperature changes lagging behind daylight changes.

Winter is conventionally observed from the December solstice to the March equinox, and summer from the June solstice to the September equinox, though these dates shift slightly each year due to differences between the calendar and astronomical years. Oceanic currents, influenced by phenomena such as El Niño–Southern Oscillation, can alter weather patterns along northern coasts. Trade winds blow east to west just above the Equator, pulling surface water westward; the Coriolis effect then bends these currents to the right, northward.

Around 30° north latitude, westerlies push the currents back east, forming a closed clockwise loop. The Coriolis effect also causes large-scale air and water flows to turn right, creating clockwise gyres in the North Atlantic and North Pacific. High-pressure weather cells rotate clockwise, while low-pressure systems like hurricanes spin counterclockwise. During the Pleistocene, lasting about 2.5 million years, the Northern Hemisphere experienced numerous glacial periods, with continental ice sheets advancing in Europe and North America at intervals of roughly 40,000 to 100,000 years.

These cold phases were separated by shorter, temperate interglacials lasting 10,000–15,000 years. The last glacial episode ended about 10,000 years ago, and Earth is now in the Holocene interglacial. The Arctic, centered on the North Pole, has cold winters and cool summers, with precipitation mainly as snow.

Within the Arctic Circle, the Sun may not set for days in summer or rise for days in winter. Between the Arctic Circle and the Tropic of Cancer lies the Northern temperate zone, where seasonal changes are generally mild. Tropical regions between the Tropic of Cancer and the Equator are hot year-round, with rainy summers and dry winters. A sundial’s shadow moves clockwise north of the subsolar point.